Active facilitation of helper dispersal by parents and siblings in the cooperatively breeding acorn woodpecker

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Here we describe active facilitation in the acorn woodpecker (Melanerpes formicivorus) by parents and siblings assisting the dispersal of helpers in their social group. Helpers in this species compete for reproductive opportunities in “power struggles” that take place when breeders of one sex die or disappear, thereby creating a reproductive vacancy. Individuals compete at power struggles in coalitions of relatives, in which larger coalitions are more likely to be victorious. Based on observations of banded birds, we found that an estimated 26% of individuals competing as part of a winning coalition at a power struggle returned to their home territory at its conclusion, suggesting that they were facilitating the dispersal of kin (generally parents or siblings) that stayed to become breeders on the new territory. In at least one group, parental and sibling facilitation was reciprocated; that is, a bird that was helped at a power struggle by a relative joined that same relative as part of a coalition at a subsequent power struggle. Dispersal facilitation is a novel means by which parents can enhance the direct fitness of offspring or siblings can enhance each other’s inclusive fitness in this highly social species. acorn woodpecker cooperative breeding dispersal facilitation nepotism parental facilitation reciprocity Significance statement Parental facilitation—being passively tolerated on the natal territory—may provide significant direct fitness benefits to helpers in cooperatively breeding species. We describe active facilitation of helper dispersal in the acorn woodpecker, where helpers compete in coalitions for reproductive opportunities at “power struggles” following the death or disappearance of breeders of one sex. About one-fourth of individuals—including both parents and siblings—competing at power struggles were apparently facilitators, assisting related helpers but then returning to their home territory rather than staying to breed on the new territory. In at least one group, dispersal facilitation was reciprocated, with a bird that was helped at a power struggle by a relative later joining that same relative as part of a coalition at a subsequent power struggle. Active dispersal facilitation by parents and siblings is an important, previously unrecognized, form of nepotistic behavior in this highly social species. Introduction Cooperative breeders are species in which individuals beyond a pair assist in the production of young at a single brood or litter (Koenig and Dickinson 2016). One of the most common forms of cooperative breeding is “helping at the nest” in which individuals, usually but not always offspring of the breeders in the group, delay their own reproduction and help provision, or otherwise assist in, raising subsequent offspring rather than attempt to breed independently (Cockburn 1998; Riehl 2013). This has led to a vibrant literature focusing on the potential ways that helping behavior may benefit the fitness of both the breeders in the group and the helpers themselves (Dickinson and Hatchwell 2004). Chief among these is the indirect fitness helpers gain—assuming, as is usually the case, they are related to the breeders—when they feed young, reduce the costs of reproduction borne by the breeders, protect young from predators or nest parasites, or otherwise contribute to the tasks needed for successful reproduction (Brown 1980; Mumme 1992; Cusick et al. 2018). Delayed dispersal by helpers can, however, yield fitness benefits in at least two additional ways. First, helpers may enhance survivorship of their parents by being vigilant of predators and reducing the risk of their parents being depredated outside the breeding season. Second, by having continued access to resources on their natal territory, the probability that helpers will disperse successfully and become a breeder on a high-quality territory may be enhanced. This latter mechanism, generally involving the offspring’s parents, is called “parental facilitation” (Brown 1987; Ekman et al. 2000; Chiarati et al. 2011). In species with helpers, parental facilitation can be considered a form of delayed reciprocity, since parents typically assist offspring that previously provided help at the parent’s nest. Prior research in the Siberian jay ( Perisoreus infaustus ) and Seychelles warbler ( Acrocephalus sechellensis ) has shown that offspring with access to parental resources have higher survivorship and are more likely to acquire breeding positions, suggesting that parental facilitation can be a powerful means of increasing offspring fitness (Ekman et al. 2004; Eikenaar et al. 2007). Our understanding of the role of parental facilitation in cooperative breeding systems is, however, limited. Here we document two forms of active facilitation—parental and sibling—in the cooperatively breeding acorn woodpecker ( Melanerpes formicivorus ). This species lives in permanently territorial groups of up to 15 (rarely more) individuals including a polygynandrous core of between one to eight cobreeding males, one to three joint-nesting females, and a variable number of nonbreeding helpers of both sexes from prior nests (Koenig et al. 2016; 2020). There is no known extra-group mating (Dickinson et al. 1995), and thus helpers are closely related to the breeders of both sexes. Reproductive vacancies in acorn woodpecker groups occur following the death or disappearance of the breeders of one sex (either males or females). Vacancies provide opportunities for helpers to attain breeding status, either by dispersing and filling a vacancy of the same sex in another group (Koenig et al. 2000), or by inheriting breeding status within their natal territory after the opposite-sex breeders in their home group disappear, creating a reproductive vacancy that is filled by a coalition of immigrant, unrelated birds (Koenig et al. 1998). Individuals attempting to fill a vacancy outside their natal group compete against birds from other groups that converge on the territory and fight in coalitions. These contests to fill reproductive vacancies, known as power struggles (Koenig 1981), can involve dozens of birds from up to several kilometers away, last for days or weeks, and are typically won by the largest competing coalition of birds. Birds in the winning coalition then become, at least potentially, the new set of cobreeders in the group (Hannon et al. 1985). Although many power struggles fit the above description and are precipitated by reproductive vacancies, this is not always the case. Furthermore, birds participating in power struggles are not always individuals that appear to be candidates for filling the reproductive vacancy even when one exists, and not all birds that fight as part of a winning coalition remain in the new group (Koenig 1981; Hannon et al. 1985; Barve et al. 2020b). If birds do not remain on the territory regardless of the success of their coalition, what is their motivation for attending the power struggle? Here we ask, for each bird identified at a series of power struggles watched intensively between 2013 and 2017, what benefit birds participating in the power struggle apparently stood to gain. Methods General methods This work was part of a long-term study of acorn woodpecker social behavior at Hastings Natural History Reservation in central coastal California, USA (36° 23’ N, 121° 33’ W), where >6,000 birds have been color-banded and their life histories recorded since 1972 (MacRoberts and MacRoberts 1976; Koenig and Mumme 1987). The Reservation consists of a mix of plant communities (Griffin 1974); those inhabited extensively by acorn woodpeckers include foothill woodland, oak savanna, and riparian woodland (Koenig and Mumme 1987). Group composition was monitored by means of censuses made at approximately bimonthly intervals. Most birds were banded either as nestlings or as adults when feeding young or roosting in cavities at night (Stanback and Koenig 1994). Power struggles are detected by raucous calls and displays of both intruding and resident individuals. Once a power struggle was encountered, we conducted one or more behavioral watches daily, observing birds through spotting scopes from blinds located in view of the group’s granary until activity returned to normal, usually after a few days but sometimes over a longer period. The data reported here are based on 11 power struggles monitored between August 2013 and August 2017 to ascertain the identity of competing individuals and the coalitions of which they were a part. In total, 58 watches totaling approximately 102 hr of observation were made. To supplement these observations, we include data from power struggles reported previously by Koenig (1981) and Hannon et al. (1985). To interpret the apparent motivation for power struggles, we determined the composition of groups prior to and at the conclusion of the power struggle. It was not unusual, however, for a power struggle to take place intermittently, sometimes over a period of weeks, before a resolution was achieved. In such cases, we considered the multiple outbreaks of fighting a single event. Unbanded birds, which inevitably make up a sizeable proportion of birds at power struggles, were not included in the analyses except when they were involved in its resolution. Categorizing birds at power struggles When, as is usually the case, a power struggle is precipitated by a reproductive vacancy, we refer to the sex of the vacancy as “sex A.” Birds observed at power struggles are referred to as “attendees.” We divided attendees into four categories: 1. Residents. Current members of the group where the power struggle took place were considered “residents.” For a power struggle of sex A, residents typically included cobreeders of sex B and any helpers of either sex that were still present in the group at the time of the power struggle. Note, however, that when several helpers of sex A are present in the group, they are sometimes able to rebuff attempts to fill the vacancy (Koenig et al. 1999). 2. Contenders. For a typical power struggle where the vacancy was of sex A, “contenders” were generally helpers of sex A from other groups whose motivation was presumably to achieve breeder status in the group where the power struggle took place. Breeders of sex A also sometimes participated in power struggles as contenders attempting to secondarily disperse (Koenig et al. 2016) and “trade up” to a breeding situation of superior quality. Contenders often competed in coalitions, usually of siblings but sometimes including breeders from their home group. If the vacancy was precipitated by the disappearance of both sexes, contenders could be helpers of either sex. If no reproductive vacancy existed initially, motivation for the power struggle was apparently to evict some or all of the resident birds. 3. Facilitators . Birds assisting contenders by fighting as part of their coalition, even though they did not, or were judged unlikely to, remain in the new group at the conclusion of the power struggle, were considered “facilitators.” We identified two classes of facilitators. The first were related breeders of either sex from the same group as one or more contenders. Such birds were apparently assisting their offspring and returned to their home territory at the conclusion of the power struggle. We considered these cases of parental facilitation. The second class of facilitators were helpers, usually but not always of sex A, that were part of a coalition fighting for the vacancy, but then, after winning the power struggle, returned to their natal group rather than staying to become a cobreeder with their siblings at the new group. These were considered cases of sibling facilitation. 4 . Others . Not all attendees fit into one of the above categories. Some individuals took advantage of the chaos of the power struggle to steal stored acorns from the granary, structures central to acorn woodpecker territories where acorns are stored in the autumn for later consumption. Other individuals, from groups adjacent to the power struggle, may have been defending their own territory from birds participating in the power struggle. We refer to birds observed at power struggles that we could not identify as residents, contenders, or facilitators as “others,” as their motivation was apparently unrelated to dispersal of themselves or their relatives. A recurring problem in our efforts to categorize individuals involved attendees that were breeders in their home group but apparently did not have any known potential helpers of the appropriate sex participating in the power struggle. Our classification of such individuals was based, as much as possible, on their individual history. If a breeder remained in the new group following the conclusion of the power struggle or if the breeder continued to exhibit behavior suggesting an interest in switching groups (such as being observed intruding at other groups or attending other power struggles), we considered it a contender attempting to disperse secondarily from its current group. If the breeder did neither of these, we placed the individual in the “other” category. Results Table 1 summarizes the power struggles monitored for this study. Combined with naturally-occurring power struggles reported by Koenig (1981) and Hannon et al. (1985), about half (47%) were motivated by female vacancies, while nearly one-third (31%) involved male vacancies (Table 2). Three (9%) involved vacancies of both sexes or took place on a vacant territory. Four (13%) occurred on a territory where there was no reproductive vacancy and resulted either in no change in group composition or eviction and replacement by the invading group; such cases apparently involved groups attempting to improve their situation by usurping a territory of superior quality. Most power struggles (81%), however, were motivated by the potential for invading birds to attain a breeding position by filling a reproductive vacancy attributable to the death or disappearance of the breeders in the group where the power struggle took place. In total, we identified 36 males and 81 females attending power struggles from groups other than the one at which the power struggle took place. Table 3 provides background information on these individuals, including the rationale for their respective categorization. The size of coalitions is not explicit in Table 3 but can be deduced by counting birds observed at the power struggle from the same group along with, in a few cases, related individuals present that had dispersed previously to another group. Some of the complexities of sibling facilitation, along with a case of apparent reciprocity, are illustrated by the histories of seven helper (H) female siblings from group PLQE at three power struggles (PS), all of which they won (Table 4). All five extant helpers participated in PS1 (Table 1) at group CAVI in August 2013. After winning that power struggle, ♀︎5151 and ♀︎5390 remained at group CAVI, while the other three birds returned to group PLQE. The next spring, H♀︎5079 and her two sisters that had previously remained at CAVI (♀︎5151 and ♀︎5390) fought as a coalition in PS3 at group ROBH, after which ♀︎5390 remained at ROBH while H♀︎5079 returned to PLQE and ♀︎5151 returned to CAVI. Later the same month, four of these sisters, again including ♀︎5151, were joined by two younger sisters (H♀︎5482 and H♀︎5486) in PS5 at group KNOL. After winning PS5, ♀︎5007 and ♀︎5079 remained along with a third bird, presumably a younger sibling fledged from a missed nest who was thus unbanded (this bird is not included in Table 4). Meanwhile, the other sisters returned to PLQE or, in the case of ♀︎5151, previously facilitated by ♀︎5007 and ♀︎5079 at PS1, to CAVI. This example illustrates that siblings unite in coalitions to compete more effectively at power struggles including, in some cases, birds that had previously dispersed and achieved breeding status elsewhere. After winning a power struggle, large coalitions often broke up, with only some of the members remaining at the new territory. In total, 39% of males and 73% of females were judged to be contenders attempting to disperse to and become a breeder on the territory where the power struggle occurred (Table 5). Thirty birds (42% of the males; 19% of the females) were judged to be facilitators, of which approximately one-fourth were parental facilitators and three-fourths sibling facilitators. The remaining 12% of birds (“others”) were apparently at the power struggle for some reason other than potentially dispersing themselves or facilitating the dispersal of relatives. Discussion Dispersal facilitation Most power struggles were initiated by a reproductive vacancy and a large fraction of the participating birds were helpers from other groups that would benefit by moving to, and achieving breeding status in, the territory where the power struggle took place (referred to as the “new” territory). These contenders were identified from groups up to 1.86 kms away and from as many as 15 different social groups (Table 3, PS10). Of particular interest are the 42% of males and 19% of females whose participation in the power struggle appeared unrelated to their likelihood of dispersing to the new territory but were instead apparently facilitating the dispersal of relatives by fighting as part of, and thus increasing the competitiveness of, their coalition. These individuals included breeders helping their offspring (parental facilitation), and offspring helping their siblings (sibling facilitation). A case of facilitation of dispersal by presumed female siblings was reported previously by Hannon et al. (1985). Both sibling and parental facilitation were common. Of the 11 power struggles investigated here, parental facilitation was identified at 4 (36%) and sibling facilitation at 8 (73%). Given the many unbanded birds typically present at power struggles, these values likely underestimate the frequency of facilitation. Facilitation increases coalition size, rendering them more likely to win power struggles (Hannon et al. 1985). What, however, is the benefit to facilitators, and why do they not remain at the new territory? Although larger coalitions of birds are more likely to win power struggles, inclusive fitness of cobreeders declines with coalition size, dramatically so for larger coalitions; the only apparent exception being that of joint-nesting female duos (Koenig et al. 2023a). Thus, birds that facilitate the dispersal of relatives may achieve greater fitness by assisting relatives to disperse and then returning home than they would by remaining in the new group as part of a large breeding coalition. In at least some cases, facilitation may be reciprocated, as illustrated by the sisters at PLQE (Table 4). Unknown is the basis on which birds in a coalition decide which individuals remain in the new territory and which do not. One possibility is that such facilitators are subordinate to the birds that stay to become breeders, a hypothesis consistent with the evidence that larger, and presumably older, individuals within broods are more successful at gaining reproductive opportunities (Koenig et al. 2011a). Contrary to the prediction that older helpers in a coalition are more likely to remain in the new group following a power struggle, however, the birds remaining in PS1 (♀︎5151 and ♀︎5390) were two of the youngest birds in the coalition. Irrespective of the factors causing some birds to return to their home territory rather than remaining to cobreed following success at a power struggle, such birds effectively act altruistically, helping relatives obtain breeding positions at some cost to themselves. A difficulty with identifying parental facilitators is excluding the possibility that breeders attending a power struggle are trying to improve their own current position by dispersing secondarily. At one end of the spectrum was B♀︎5734 (PS10 and PS11). This bird bred at HORS in 2015 and 2016, but the group apparently failed to initiate a nest either year. Prior to the 2017 breeding season, B♀︎5734 was observed foraying and participating in power struggles at several territories. We therefore judged that she was likely prospecting for a superior breeding position and was a contender at these power struggles. Alternatively, B♂︎4051 attended PS9 with his son (H♂︎5658) from the prior year. After they won the power struggle, ♂︎5658 remained as the new breeder while ♂︎4051 returned home to BINO. In this case, B♂︎4051’s participation facilitated the successful dispersal of his son who, as a singleton, would have been unlikely to win the power struggle otherwise. Facilitation and reciprocity Offspring acorn woodpeckers almost always help at the nest, a behavior that enhances reproductive success under most environmental conditions (Koenig et al. 2011b). Thus, when breeders assist helper dispersal by increasing the size of their coalition at a power struggle, they are reciprocating the help they received while breeding. The opposite of “pay-to-stay” (Kokko et al. 2002; Bergmüller and Taborsky 2005), helpers can be considered being repaid for their prior assistance. Sibling facilitation of offspring dispersal can also involve reciprocity. Birds that acquired a breeding position previously with the assistance of siblings may temporarily rejoin those same siblings to help compete as a coalition for a subsequent vacancy. By facilitating the dispersal of kin, such birds are also increasing the presence of relatives on the landscape, thereby providing opportunities for refuge (secondary dispersal) should a bird later lose its granary or be evicted from its territory. The clearest cases of reciprocity we documented are detailed in Table 4. Parental facilitation as envisioned by Brown (1987) encompassed three behaviors: (1) increased survival of offspring as a consequence of not being evicted from their home territory; (2) increased chance of achieving breeding status associated with using the home territory as a base from which to foray and search for reproductive vacancies; and (3) an increased possibility of inheriting and achieving breeding status on their home territory. All are potentially applicable to acorn woodpeckers (Barve et al. 2020a; Koenig et al. 2023b). Such behaviors are passive, only involving parents tolerating the presence of offspring. In contrast, the behaviors we describe here involve facilitators actively participating in coalitions that fight to fill a reproductive vacancy at a group to which their offspring or siblings will potentially disperse and subsequently breed. We are aware of no comparable behavior previously described in a cooperative breeder. Participants in power struggles Based on an automated radio-telemetry system, Barve et al. (2020b) reported on the birds detected at three putative female power struggles. Of the birds detected, those that were considered candidates for potentially filling the vacancy (female helpers) were referred to as “warriors.” Breeder females and any males from other groups were referred to as “spectators,” since they either already had breeding status elsewhere or were presumed to be of the wrong sex to potentially fill the vacancy that initiated the power struggle. Birds identified as spectators spent an average of 52 min day -1 at power struggles and were hypothesized to be gathering social information—that is, gaining information about the group and other birds present at the power struggle. This hypothesis is consistent with the extensive knowledge that acorn woodpeckers apparently have about the social status of other individuals in the population (Pardo et al. 2018; 2020a; 2020b). Our analyses here, based on behavioral observations, clarifies the motivation of many of the participants at power struggles that are not candidates to fill an initiating reproductive vacancy. Of 44 birds attending power struggles that were neither residents nor contenders, 30 (68%) were classified as either parental or sibling facilitators. The motivation of the remaining 14 (32%) nonresidents and noncontenders was apparently for a reason other than facilitating dispersal of kin. In some of these latter cases, birds may indeed be obtaining information, either of the territory where the power struggle took place or of other attendees at the power struggle. If so, the information being acquired, and how such information might eventually benefit them, remains to be determined. Facilitation and fitness Quantifying the benefit of joining a coalition to enhance its competitiveness at a power struggle is difficult. Ideally, it would be necessary to know the success rate of different-sized coalitions, a value that is likely to differ depending on the season, population density, quality of the territory, and other factors, including the fitness consequences of breeding in coalitions—which itself has proved challenging to determine (Mumme et al. 1988; Barve et al. 2021; Koenig et al. 2023a). Estimating the success rate of coalitions is likely to remain out of reach until it is possible to track the fate of birds emigrating out of the study area. Although current tracking technology has yielded insight on the foray behavior of acorn woodpeckers (Barve et al. 2020a), much remains to be done before it will be possible to resolve the dispersal-mortality confound of finite study areas such as ours (Koenig et al. 1996). Power struggles are chaotic affairs involving a great deal of fighting and physical contact. It is not unusual for birds to fall to the ground, locked leg-to-leg in combat (Koenig 1981). We have observed occasional injuries, and birds participating in power struggles are clearly vulnerable to predation. Moreover, given that power struggles can start within minutes of a vacancy arising (Hannon et al. 1987), parental facilitators fighting elsewhere risk losing their own territory when leaving it undefended. There are thus significant costs to participating in power struggles. Facilitators apparently gain more than they risk by increasing the chances of close relatives gaining a reproductive opportunity, particularly if the relative has no other same-sex siblings and is thus unlikely to win a power struggle on its own. It is also possible, however, that facilitators do not fight as vigorously or spend as much time fighting as contenders that eventually gain a reproductive opportunity after winning a power struggle. We currently do not have data to examine this possibility. To estimate inclusive fitness of social behaviors like breeding in coalitions, one needs to compare fitness when breeding singly (Koenig et al. 2023a). The difficulties in determining the costs and benefits of facilitation, however, render its inclusive fitness consequences unclear. Nonetheless, parental and sibling facilitation of dispersal provide yet another example of the importance of kin selection to the evolution of social behavior (Hamilton 1964a; 1964b). Declarations Acknowledgments We thank the reviewers for comments and Hastings Reservation (DOI: 10.21973/N33Q0G) for hosting the project since its inception by Michael and Barbara MacRoberts in 1968. We especially wish to thank our colleagues and the 250+ field and assistants who have contributed to the project over the years. Author contributions NDGH and ELW conceived the study; NDGH collected the observational data at the power struggles; all authors helped collect background data used to interpret results. WDK wrote the initial draft of the paper based in part on NDGH’s PhD thesis; all authors reviewed and edited subsequent drafts. Funding This work was supported by the North American Bluebird Society and Sigma Xi Grants in Aid of Research to NDGH, National Science Foundation (NSF) grant IOS-1455881 to WDK, and NSF grant IOS-1455900 to ELW. Ethics approval This study was conducted under the auspices of the Animal Care and Use Committees of Old Dominion University (protocol 12-001 and 15-001), the University of California, Berkeley (protocol R010-0412), and Cornell University (protocol 2008-0185). Competing interests The authors certify that they have no financial or non-financial competing interests. Data availability All data are available in the tables. References Barve S, Hagemeyer NDG, Winter RE, Chamberlain SD, Koenig WD, Winkler DW, Walters EL (2020a) Wandering woodpeckers: foray behavior in a social bird. 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J Field Ornithol 65:70-75 Tables Table 1 Summary of power struggles (PS) monitored for this study PS Dates Group Original cause Result Comments 1 11–12 Aug 2013 CAVI ♀︎ vacancy combined with temporary capture of 2 of the 3 ♂︎♂︎ ♀︎ vacancy filled by a ♀︎ from PLQE; ♂︎♂︎ evicted and replaced by a coalition of 3 ♂︎♂︎ from BLMP ♀︎had been gone for some time, but the PS started following 2 of the ♂︎♂︎ being captured and held temporarily for processing; the ♂︎♂︎ were subsequently driven out by a large coalition from group BLMP (one of which had previously moved to MISH) 2 30 Mar & 2 May 2014 JAIM ♀︎ vacancy Filled by a ♀︎ from KNOL ♀︎ replaced in March; fighting resumed into May but did not lead to further change in group composition 3 7 Mar 2014 ROBH ♀︎ vacancy Filled by a coalition of 2 ♀︎♀︎ from CAVI 4 25 Mar & 2 May 2014 PLQE ♂︎ vacancy Entire group evicted and replaced Territory taken over by UPBA group and forced into an adjacent territory 5 18–25 Mar 2014 KNOL ♀︎ vacancy Filled by a coalition of 3 ♀︎♀︎ from PLQE 6 14–15 May 2014 LHAY ♂︎ vacancy ♀︎ breeder evicted, replaced by coalition of 2 ♀︎♀︎ With new ♀︎♀︎, the 2 helper ♂︎♂︎ in the group inherited and became breeders 7 8 Apr 2015 UPBA Vacant territory New group Colonized by a coalition of 2 ♂︎♂︎ from PLQE and a ♀︎ from CABI 8 2–4 Apr 2016 A1 ♀︎ vacancy Filled by a coalition of 3 ♀︎♀︎ from KOUT 9 3–4 Apr 2016 RE10 Vacant territory New group Colonized by a ♂︎ from BINO and a coalition of 2 NOBA ♀︎♀︎ 10 Mar–Aug 2017 PLQE ♀︎ vacancy Eventually filled by a coalition of 4 ♀︎♀︎ from JAIM PS continued intermittently for months 11 5–6 Aug 2017 1800 No initial vacancy ♂︎ replaced by a coalition of 2 NOBA ♂︎♂︎ Started with ♀︎♀︎ fighting but after several days the breeder ♂︎ disappeared Table 2 Summary of the apparent causes of power struggles monitored for this study and reported by Koenig (1981) and Hannon et al. (1985); excluded are power struggles of unknown origin and those initiated by experimental removals Apparent cause This study Koenig (1981) Hannon et al. (1985) Total ♀︎ vacancy 5 (45%) 7 (47%) 3 (50%) 15 (47%) ♂︎ vacancy 2 (18%) 5 (33%) 3 (50%) 10 (31%) Vacancy of both sexes 1 (9%) a — — 1 (3%) Vacant territory 2 (18%) — — 2 (6%) No initial vacancy 1 (9%) 3 (20%) b — 4 (13%) N power struggles 11 15 6 32 a Includes PS1 (Table 1), where there was a female vacancy but the power struggle started following the capture of two of the three males for unrelated reasons. b In two of these three cases there was no change in group composition, while in the third the entire group was expelled. Table 3 Banded acorn woodpeckers observed at the power struggles monitored for this study and their apparent motivation for attendance PS Group Residents Contenders Facilitators Others Notes 1 CAVI B♂︎3165x B♂︎3284x H♂︎5094x H♂︎5378x B♂︎4621 (BLMP) H♂︎4933 (BLMP) H♂︎4935 (BLMP) H♂︎5278 (SHIL) H♀︎5151 (PLQE) H♀︎5325 (CABI) H♀︎5390 (PLQE) H♂︎5376s (BLMP) 1 H♂︎5377s (BLMP) 1 H♀︎5007s (PLQE) 1 H♀︎5079s (PLQE) 1 H♀︎5389s (PLQE) 1 B♀︎4938 (JAIM) 2 1 These were all siblings of the birds that displaced the residents but returned home rather than remain at CAVI at the conclusion of the PS. 2 B♀︎4938 was observed at CAVI taking acorns from the granary to her home group JAIM, which was adjacent to CAVI. 2 JAIM B♂︎4890 H♀︎5103 (KNOL) B♀︎4854 (UPBA) 3 H♀︎4470 (SHIL) H♀︎5091 (SHW) H♀︎5430 (PIPE) 3 B♀︎4854 was involved in PSs at JAIM (PS2) and at PLQE (PS4), territories very close to each other where PSs occurred nearly simultaneously. Her involvement at PS2 may have been secondary to the one at PLQE (where she ultimately moved), but she was apparently prospecting to leave UPBA and thus categorized as a contender . 3 ROBH B♂︎4884 B♂︎5220 H♂︎5583inh H♂︎5585inh B♀︎5390 (CAVI) 4 H♀︎5079s (PLQE) 4 B♀︎5151s (CAVI) 4 4 B♀︎5390 stayed at CAVI following PS1 but moved here after being facilitated by two of her sisters, H♀︎5079 (still at group PLQE) and B♀︎5151, her sister who had moved with her to group CAVI following PS1. 4 PLQE H♂︎5152x H♂︎5153x B♀︎4629x H♀︎5151x H♀︎5389x H♀︎5482x H♀︎5486x B♂︎5006 (UPBA) H♂︎5303 (DIPS) H♂︎5474 (DIPS) H♂︎5454 (PLAN) B♀︎4854 (UPBA) B♀︎5014 (UPBA) H♀︎5317 (CHIM) H♀︎5370 (SHIL) B♂︎4890 (JAIM) 5 B♀︎5103 (JAIM) 5 5 B♂︎4890 had been a successful breeder at JAIM for over 2 years, while B♀︎5103 had recently moved to JAIM (PS2) and remained there until 2017. Thus neither bird was likely to be prospecting, nor did they have offspring whose dispersal they might have been facilitating. Also, JAIM is adjacent to PLQE, making it likely they were defending their own territory or drawn into the PS for some other reason. 5 KNOL B♂︎3399 B♂︎3753 B♂︎5059 H♀︎5007 (PLQE) H♀︎5079 (PLQE) ♀︎NOBA (PLQE) B♀︎5151s (CAVI) 6 H♀︎5389s (PLQE) H♀︎5482s (PLQE) H♀︎5486s (PLQE) ♂︎5204 (HORS) 7 6 B♀︎5151 had previously moved to CAVI but was born at PLQE and a sister of the 3 PLQE ♀︎♀︎ that remained (including the ♀︎NOBA, who was presumably from a missed nest). 7 ♂︎5204 had not been seen since leaving his home group early in 2013. As a ♂︎ at what was an unambiguous ♀︎PS with no known relatives whose dispersal he might have been facilitating, we classified him as other . 6 LHAY H♂︎4928inh H♂︎5251inh B♀︎4570x B♀︎4590x H♀︎5476 (DIPS) H♀︎5247 (BLM2) H♀︎5140 (HORS) B♂︎5250s (BRWN) 8 H♂︎5202s (HORS) H♂︎5207s (HORS) H♂︎5416s (HORS) 8 B♂︎5250 had previously moved to BRWN but was born at LHAY and was thus a sibling of the two helper ♂︎residents, H♂︎4928 and H♂︎5251. He therefore was presumably helping them defend the territory against intruders and was considered a sibling facilitator . He later switched territories and returned home to LHAY, joining H♂︎5251 (now B♂︎5251) as a cobreeder. 7 UPBA H♂︎5562 (PLQE) H♂︎5698 (PLQE) H♀︎4904 (CABI) B♂︎5006p (PLQE) 9 B♂︎5153p (PLQE) 9 H♂︎5700s (PLQE) 9 H♂︎5701s (PLQE) 9 B♀︎4854p (PLQE) 9 9 These birds returned to PLQE following the PS, and thus were all considered facilitators of the 2 helpers that remained. 8 A1 B♂︎4561 H♂︎5750inh H♀︎5309 (KOUT) H♀︎5642 (KOUT) H♀︎5740 (KOUT) B♀︎5155 (LAMB) 10 H♀︎5349 (BKOK) H♀︎5383 (LA2) H♀︎5465 (LA2) H♀︎5741s (KOUT) B♂︎4568 (UA2) 11 H♂︎5265 (UA2) 11 H♂︎5658 (BINO) 11 10 B♀︎5155 had previously inherited breeder status at LAMB in late 2015. However, the group did not appear to have bred in 2016 and thus B♀︎5155 is considered a contender potentially prospecting for a new group. 11 These 3 males from nearby groups had no known ♀︎♀︎ relatives participating in this ♀︎PS, and may have been defending their own territories. We thus classified them as others . 9 RE10 H♂︎5658 (BINO) H♂︎5739 (KOUT) 13 2 NOBA ♀︎♀︎ (UNK) B♂︎4051p (BINO) 12 H♀︎5825s (KOUT) 13 12 B♂︎4051 fought at this PS as a parental facilitator of H♂︎5658, his son from 2015. 13 H♂︎5739 and H♀︎5825 were siblings that both participated in the PS. Since RE10 had been vacant, either, but not both, could have remained and bred had they won (which they did not). We therefore classified one of them (H♂︎5739, who was older) as a contender and H♀︎5825 as a sibling facilitator . 10 PLQE B♂︎5006 B♂︎5152 B♂︎5153 H♂︎5878 H♀︎5876x B♀︎5103 (JAIM) H♀︎5944 (JAIM) H♀︎5945 (JAIM) H♀︎5946 (JAIM) B♀︎4713 (BUCK) 14 H♀︎5192 (PIPE) H♀︎5498 (CECN) H♀︎5715 (KNOL) B♀︎5734 (HORS) 15 H♀︎5771 (1500) H♀︎5912 (LOLF) B♀︎6001 (CABI) 16 H♀︎5970 (CABI) 16 H♀︎5972 (MACR) H♀︎5903 (PLAN) H♀︎5938 (Y) H♀︎5950 (UPBA) H♀︎5954 (CHIM) H♀︎5955 (CHIM) H♀︎5979 (ROBH) ♀︎6005 (UNK) H♂︎6002s (CHIM) 17 H♂︎5891s (JAIM) B♂︎5698p (UPBA) 18 H♂︎5952s (UPBA) 18 B♀︎4904p (UPBA) 18 H♂︎5880 (CAVI) 19 H♂︎5881 (CAVI) 19 B♀︎4629 (CAVI) 19 B♀︎4493 (FNCH) 20 B♀︎4968 (RE03) 21 B♀︎5209 (AMAD) 21 B♀︎5659 (MIKE) 22 14 Although B♀︎4713 had been a breeder at BUCK since 2013, she apparently left the group after the long-time breeder ♂︎disappeared in early 2016. Thus, we considered her a contender interested in switching territories. 15 B♀︎5734 bred at HORS in 2015 and 2016, but the group failed to initiate a nest either year. By 2017 she was foraying, presumably in search of a new breeding opportunity, and thus we considered her a contender both here and at PS11. 16 At the time of this PS, CABI had no breeder ♂︎. Thus, although B♀︎6001 was apparently the breeder ♀︎at CABI, we assumed she was prospecting for a new territory and considered her a contender along with her daughter H♀︎5970. 17 The origin of H♂︎6002 (banded at CHIM early in 2017) was unclear, but he was thought to be from a missed nest, and thus a sibling of H♀︎5954 and H♀︎5955. We thus classified him as a sibling facilitator . 18 Both B♂︎5698 and B♀︎4904 bred at UPBA in 2017 and 2018 and were thus assumed to be parental facilitators of H♀︎5950, their daughter from 2016. Since this was a ♀︎ vacancy, we classified H♂︎5952 as a sibling facilitator of his sister, H♀︎5950. 19 These three birds were from the adjacent CAVI territory that did not contain any helper ♀︎♀︎ observed at the PS. Further, B♀︎4629 bred successfully at CAVI in both 2015 and 2016 and was still breeding there as of 2022. We thus classified them as other . 20 B♀︎4493 was a long-time breeder at her home group (FNCH) and was considered unlikely to be prospecting for a new territory. Group FNCH, however, contained one helper ♀, who was not seen at the PS. We thus considered her other , but it is possible that the helper ♀ was missed and that B♀︎4493 was a parental facilitator . 21 Females B♀︎4968, and B♀︎5209 were long-time breeders at their home groups and were judged unlikely to be interested in switching territories. Neither of their home groups contained a helper ♀︎ who might have competed at the PS, and thus we considered them others . 22 B♀︎5659 inherited her natal territory (MIKE) in Sept. 2016 and bred there in 2017 after the conclusion of this PS. There was no helper ♀︎♀︎ at MIKE in 2017, and we thus considered her other . 11 1800 B♂︎4589x B♀︎4261 ♂︎6069 (UNK) ♂︎NOBA (UNK) H♀︎5636 (1500) H♀︎5771 (1500) H♀︎5774 (1500) B♀︎5734 (HORS) 15 H♀︎5763 (1600) H♀︎5855 (1600) H♀︎5866 (SOSP) H♀︎5712 (SHIL) H♀︎5990 (SHIL) B♀︎4672p (1500) 23 B♀︎5813p (SOSP) 23 15 See PS10. 23 These 2 ♀︎♀︎ were breeders in their home groups in 2016 and 2017 and were likely present at this PS as parental facilitators of their daughters (H♀︎5636, H♀︎5771, and H♀︎5774 from group 1500 and H♀︎5866 from group SOSP, respectively). Birds winning the power struggle and remaining in the territory are highlighted. B=breeder; H=helper; 4-letter code in parentheses is the group from which the bird originated; PS numbers refer to power struggles in Table 1; “x” indicates a bird leaving or being evicted from the group; “s” indicates a sibling facilitator; “p” a parental facilitator; “inh” indicates a bird that inherited the territory following the power struggle. NOBA = unbanded bird; UNK = unknown group. Table 4 Histories of seven helper female siblings from group PLQE at three power struggles in 2013 and 2014, all of which they won Bird Year fledged PS1: CAVI (2013) PS3: ROBH (2014) PS5: KNOL (2014) H♀5007 2010 Returned to PLQE Stayed H♀5079 2011 Returned to PLQE Returned to PLQE Stayed H♀5151 2012 Stayed Returned to CAVI Returned to CAVI H♀5389 2012 Returned to PLQE Returned to PLQE H♀5390 2012 Stayed Stayed H♀5482 2013 Returned to PLQE H♀5486 2013 Returned to PLQE Empty cells designate birds not observed at the power struggle (either not present or not alive). Table 5 Summary of attendees at power struggles (excluding residents) Category Males Females Total Contenders 14 (39%) 59 (73%) 73 (62%) Parental facilitators 4 (11%) 4 (5%) 8 (7%) Sibling facilitators 11 (31%) 11 (14%) 22 (19%) Others 7 (19%) 7 (9%) 14 (12%) N birds 36 81 117 Cite Share Download PDF Status: Published Journal Publication published 06 Aug, 2024 Read the published version in Behavioral Ecology and Sociobiology → Version 1 posted Editorial decision: Major Revisions Needed 23 Jun, 2024 Reviewers agreed at journal 08 Feb, 2024 Reviewers invited by journal 04 Feb, 2024 Editor assigned by journal 24 Jan, 2024 First submitted to journal 20 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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We describe active facilitation of helper dispersal in the acorn woodpecker, where helpers compete in coalitions for reproductive opportunities at \u0026ldquo;power struggles\u0026rdquo; following the death or disappearance of breeders of one sex. About one-fourth of individuals\u0026mdash;including both parents and siblings\u0026mdash;competing at power struggles were apparently facilitators, assisting related helpers but then returning to their home territory rather than staying to breed on the new territory. In at least one group, dispersal facilitation was reciprocated, with a bird that was helped at a power struggle by a relative later joining that same relative as part of a coalition at a subsequent power struggle. Active dispersal facilitation by parents and siblings is an important, previously unrecognized, form of nepotistic behavior in this highly social species.\u0026nbsp;\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eCooperative breeders are species in which individuals beyond a pair assist in the production of young at a single brood or litter (Koenig and Dickinson 2016). One of the most common forms of cooperative breeding is \u0026ldquo;helping at the nest\u0026rdquo; in which individuals, usually but not always offspring of the breeders in the group, delay their own reproduction and help provision, or otherwise assist in, raising subsequent offspring rather than attempt to breed independently (Cockburn 1998; Riehl 2013). This has led to a vibrant literature focusing on the potential ways that helping behavior may benefit the fitness of both the breeders in the group and the helpers themselves (Dickinson and Hatchwell 2004). Chief among these is the indirect fitness helpers gain\u0026mdash;assuming, as is usually the case, they are related to the breeders\u0026mdash;when they feed young, reduce the costs of reproduction borne by the breeders, protect young from predators or nest parasites, or otherwise contribute to the tasks needed for successful reproduction (Brown 1980; Mumme 1992; Cusick et al. 2018).\u003c/p\u003e\n\u003cp\u003eDelayed dispersal by helpers can, however, yield fitness benefits in at least two additional ways. First, helpers may enhance survivorship of their parents by being vigilant of predators and reducing the risk of their parents being depredated outside the breeding season. Second, by having continued access to resources on their natal territory, the probability that helpers will disperse successfully and become a breeder on a high-quality territory may be enhanced. This latter mechanism, generally involving the offspring\u0026rsquo;s parents, is called \u0026ldquo;parental facilitation\u0026rdquo; (Brown 1987; Ekman et al. 2000; Chiarati et al. 2011). In species with helpers, parental facilitation can be considered a form of delayed reciprocity, since parents typically assist offspring that previously provided help at the parent\u0026rsquo;s nest. Prior research in the Siberian jay (\u003cem\u003ePerisoreus infaustus\u003c/em\u003e) and Seychelles warbler (\u003cem\u003eAcrocephalus sechellensis\u003c/em\u003e) has shown that offspring with access to parental resources have higher survivorship and are more likely to acquire breeding positions, suggesting that parental facilitation can be a powerful means of increasing offspring fitness (Ekman et al. 2004; Eikenaar et al. 2007). Our understanding of the role of parental facilitation in cooperative breeding systems is, however, limited.\u003c/p\u003e\n\u003cp\u003eHere we document two forms of active facilitation\u0026mdash;parental and sibling\u0026mdash;in the cooperatively breeding acorn woodpecker (\u003cem\u003eMelanerpes formicivorus\u003c/em\u003e). This species lives in permanently territorial groups of up to 15 (rarely more) individuals including a polygynandrous core of between one to eight cobreeding males, one to three joint-nesting females, and a variable number of nonbreeding helpers of both sexes from prior nests (Koenig et al. 2016; 2020). There is no known extra-group mating (Dickinson et al. 1995), and thus helpers are closely related to the breeders of both sexes.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eReproductive vacancies in acorn woodpecker groups occur following the death or disappearance of the breeders of one sex (either males or females). Vacancies provide opportunities for helpers to attain breeding status, either by dispersing and filling a vacancy of the same sex in another group (Koenig et al. 2000), or by inheriting breeding status within their natal territory after the opposite-sex breeders in their home group disappear, creating a reproductive vacancy that is filled by a coalition of immigrant, unrelated birds (Koenig et al. 1998). Individuals attempting to fill a vacancy outside their natal group compete against birds from other groups that converge on the territory and fight in coalitions. These contests to fill reproductive vacancies, known as power struggles (Koenig 1981), can involve dozens of birds from up to several kilometers away, last for days or weeks, and are typically won by the largest competing coalition of birds. Birds in the winning coalition then become, at least potentially, the new set of cobreeders in the group (Hannon et al. 1985).\u003c/p\u003e\n\u003cp\u003eAlthough many power struggles fit the above description and are precipitated by reproductive vacancies, this is not always the case. Furthermore, birds participating in power struggles are not always individuals that appear to be candidates for filling the reproductive vacancy even when one exists, and not all birds that fight as part of a winning coalition remain in the new group (Koenig 1981; Hannon et al. 1985; Barve et al. 2020b). If birds do not remain on the territory regardless of the success of their coalition, what is their motivation for attending the power struggle? Here we ask, for each bird identified at a series of power struggles watched intensively between 2013 and 2017, what benefit birds participating in the power struggle apparently stood to gain.\u0026nbsp;\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eGeneral methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was part of a long-term study of acorn woodpecker social behavior at Hastings Natural History Reservation in central coastal California, USA (36\u0026deg; 23\u0026rsquo; N, 121\u0026deg; 33\u0026rsquo; W), where \u0026gt;6,000 birds have been color-banded and their life histories recorded since 1972 (MacRoberts and MacRoberts 1976; Koenig and Mumme 1987). The Reservation consists of a mix of plant communities (Griffin 1974); those inhabited extensively by acorn woodpeckers include foothill woodland, oak savanna, and riparian woodland (Koenig and Mumme 1987). Group composition was monitored by means of censuses made at approximately bimonthly intervals. Most birds were banded either as nestlings or as adults when feeding young or roosting in cavities at night (Stanback and Koenig 1994).\u003c/p\u003e\n\u003cp\u003ePower struggles are detected by raucous calls and displays of both intruding and resident individuals. Once a power struggle was encountered, we conducted one or more behavioral watches daily, observing birds through spotting scopes from blinds located in view of the group\u0026rsquo;s granary until activity returned to normal, usually after a few days but sometimes over a longer period. The data reported here are based on 11 power struggles monitored between August 2013 and August 2017 to ascertain the identity of competing individuals and the coalitions of which they were a part. In total, 58 watches totaling approximately 102 hr of observation were made. To supplement these observations, we include data from power struggles reported previously by Koenig (1981) and Hannon et al. (1985). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo interpret the apparent motivation for power struggles, we determined the composition of groups prior to and at the conclusion of the power struggle. It was not unusual, however, for a power struggle to take place intermittently, sometimes over a period of weeks, before a resolution was achieved. In such cases, we considered the multiple outbreaks of fighting a single event. Unbanded birds, which inevitably make up a sizeable proportion of birds at power struggles, were not included in the analyses except when they were involved in its resolution.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCategorizing birds at power struggles\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWhen, as is usually the case, a power struggle is precipitated by a reproductive vacancy, we refer to the sex of the vacancy as \u0026ldquo;sex A.\u0026rdquo; Birds observed at power struggles are referred to as \u0026ldquo;attendees.\u0026rdquo; We divided attendees into four categories:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e1. Residents.\u0026nbsp;\u003c/em\u003eCurrent members of the group where the power struggle took place were considered \u0026ldquo;residents.\u0026rdquo; For a power struggle of sex A, residents typically included cobreeders of sex B and any helpers of either sex that were still present in the group at the time of the power struggle. Note, however, that when several helpers of sex A are present in the group, they are sometimes able to rebuff attempts to fill the vacancy (Koenig et al. 1999).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2. Contenders.\u003c/em\u003e For a typical power struggle where the vacancy was of sex A, \u0026ldquo;contenders\u0026rdquo; were generally helpers of sex A from other groups whose motivation was presumably to achieve breeder status in the group where the power struggle took place. Breeders of sex A also sometimes participated in power struggles as contenders attempting to secondarily disperse (Koenig et al. 2016) and \u0026ldquo;trade up\u0026rdquo; to a breeding situation of superior quality. Contenders often competed in coalitions, usually of siblings but sometimes including breeders from their home group. If the vacancy was precipitated by the disappearance of both sexes, contenders could be helpers of either sex. If no reproductive vacancy existed initially, motivation for the power struggle was apparently to evict some or all of the resident birds.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e3. Facilitators\u003c/em\u003e. Birds assisting contenders by fighting as part of their coalition, even though they did not, or were judged unlikely to, remain in the new group at the conclusion of the power struggle, were considered \u0026ldquo;facilitators.\u0026rdquo; We identified two classes of facilitators. The first were related breeders of either sex from the same group as one or more contenders. Such birds were apparently assisting their offspring and returned to their home territory at the conclusion of the power struggle. We considered these cases of parental facilitation. The second class of facilitators were helpers, usually but not always of sex A, that were part of a coalition fighting for the vacancy, but then, after winning the power struggle, returned to their natal group rather than staying to become a cobreeder with their siblings at the new group. These were considered cases of sibling facilitation.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4\u003c/em\u003e.\u003cem\u003e\u0026nbsp;Others\u003c/em\u003e. Not all attendees fit into one of the above categories. Some individuals took advantage of the chaos of the power struggle to steal stored acorns from the granary, structures central to acorn woodpecker territories where acorns are stored in the autumn for later consumption. Other individuals, from groups adjacent to the power struggle, may have been defending their own territory from birds participating in the power struggle. We refer to birds observed at power struggles that we could not identify as residents, contenders, or facilitators as \u0026ldquo;others,\u0026rdquo; as their motivation was apparently unrelated to dispersal of themselves or their relatives.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA recurring problem in our efforts to categorize individuals involved attendees that were breeders in their home group but apparently did not have any known potential helpers of the appropriate sex participating in the power struggle. Our classification of such individuals was based, as much as possible, on their individual history. If a breeder remained in the new group following the conclusion of the power struggle or if the breeder continued to exhibit behavior suggesting an interest in switching groups (such as being observed intruding at other groups or attending other power struggles), we considered it a contender attempting to disperse secondarily from its current group. If the breeder did neither of these, we placed the individual in the \u0026ldquo;other\u0026rdquo; category.\u0026nbsp;\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eTable 1 summarizes the power struggles monitored for this study. Combined with naturally-occurring power struggles reported by Koenig (1981) and Hannon et al. (1985), about half (47%) were motivated by female vacancies, while nearly one-third (31%) involved male vacancies (Table 2). Three (9%) involved vacancies of both sexes or took place on a vacant territory. Four (13%) occurred on a territory where there was no reproductive vacancy and resulted either in no change in group composition or eviction and replacement by the invading group; such cases apparently involved groups attempting to improve their situation by usurping a territory of superior quality. Most power struggles (81%), however, were motivated by the potential for invading birds to attain a breeding position by filling a reproductive vacancy attributable to the death or disappearance of the breeders in the group where the power struggle took place.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn total, we identified 36 males and 81 females attending power struggles from groups other than the one at which the power struggle took place. Table 3 provides background information on these individuals, including the rationale for their respective categorization. The size of coalitions is not explicit in Table 3 but can be deduced by counting birds observed at the power struggle from the same group along with, in a few cases, related individuals present that had dispersed previously to another group.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSome of the complexities of sibling facilitation, along with a case of apparent reciprocity, are illustrated by the histories of seven helper (H) female siblings from group PLQE at three power struggles (PS), all of which they won (Table 4). All five extant helpers participated in PS1 (Table 1) at group CAVI in August 2013. After winning that power struggle,\u0026nbsp;♀︎5151 and\u0026nbsp;♀︎5390 remained at group CAVI, while the other three birds returned to group PLQE. The next spring, H♀︎5079 and her two sisters that had previously remained at CAVI (♀︎5151 and\u0026nbsp;♀︎5390) fought as a coalition in PS3 at group ROBH, after which\u0026nbsp;♀︎5390 remained at ROBH while H♀︎5079 returned to PLQE and\u0026nbsp;♀︎5151\u003cem\u003e\u0026nbsp;\u003c/em\u003ereturned to CAVI. Later the same month, four of these sisters, again including\u0026nbsp;♀︎5151, were joined by two younger sisters (H♀︎5482 and H♀︎5486) in PS5 at group KNOL. After winning PS5,\u0026nbsp;♀︎5007 and\u0026nbsp;♀︎5079 remained along with a third bird, presumably a younger sibling fledged from a missed nest who was thus unbanded (this bird is not included in Table 4). Meanwhile, the other sisters returned to PLQE or, in the case of\u0026nbsp;♀︎5151, previously facilitated by\u0026nbsp;♀︎5007 and\u0026nbsp;♀︎5079 at PS1, to CAVI. This example illustrates that siblings unite in coalitions to compete more effectively at power struggles including, in some cases, birds that had previously dispersed and achieved breeding status elsewhere. After winning a power struggle, large coalitions often broke up, with only some of the members remaining at the new territory.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn total, 39% of males and 73% of females were judged to be contenders attempting to disperse to and become a breeder on the territory where the power struggle occurred (Table 5). Thirty birds (42% of the males; 19% of the females) were judged to be facilitators, of which approximately one-fourth were parental facilitators and three-fourths sibling facilitators. The remaining 12% of birds (\u0026ldquo;others\u0026rdquo;) were apparently at the power struggle for some reason other than potentially dispersing themselves or facilitating the dispersal of relatives.\u0026nbsp;\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u003cstrong\u003eDispersal facilitation\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMost power struggles were initiated by a reproductive vacancy and a large fraction of the participating birds were helpers from other groups that would benefit by moving to, and achieving breeding status in, the territory where the power struggle took place (referred to as the \u0026ldquo;new\u0026rdquo; territory). These contenders were identified from groups up to 1.86 kms away and from as many as 15 different social groups (Table 3, PS10). Of particular interest are the 42% of males and 19% of females whose participation in the power struggle appeared unrelated to their likelihood of dispersing to the new territory but were instead apparently facilitating the dispersal of relatives by fighting as part of, and thus increasing the competitiveness of, their coalition. These individuals included breeders helping their offspring (parental facilitation), and offspring helping their siblings (sibling facilitation). A case of facilitation of dispersal by presumed female siblings was reported previously by Hannon et al. (1985).\u003c/p\u003e\n\u003cp\u003eBoth sibling and parental facilitation were common. Of the 11 power struggles investigated here, parental facilitation was identified at 4 (36%) and sibling facilitation at 8 (73%). Given the many unbanded birds typically present at power struggles, these values likely underestimate the frequency of facilitation. Facilitation increases coalition size, rendering them more likely to win power struggles (Hannon et al. 1985). What, however, is the benefit to facilitators, and why do they not remain at the new territory?\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAlthough larger coalitions of birds are more likely to win power struggles, inclusive fitness of cobreeders declines with coalition size, dramatically so for larger coalitions; the only apparent exception being that of joint-nesting female duos (Koenig et al. 2023a). Thus, birds that facilitate the dispersal of relatives may achieve greater fitness by assisting relatives to disperse and then returning home than they would by remaining in the new group as part of a large breeding coalition. In at least some cases, facilitation may be reciprocated, as illustrated by the sisters at PLQE (Table 4).\u003c/p\u003e\n\u003cp\u003eUnknown is the basis on which birds in a coalition decide which individuals remain in the new territory and which do not. One possibility is that such facilitators are subordinate to the birds that stay to become breeders, a hypothesis consistent with the evidence that larger, and presumably older, individuals within broods are more successful at gaining reproductive opportunities (Koenig et al. 2011a). Contrary to the prediction that older helpers in a coalition are more likely to remain in the new group following a power struggle, however, the birds remaining in PS1 (♀︎5151 and ♀︎5390) were two of the youngest birds in the coalition. Irrespective of the factors causing some birds to return to their home territory rather than remaining to cobreed following success at a power struggle, such birds effectively act altruistically, helping relatives obtain breeding positions at some cost to themselves.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA difficulty with identifying parental facilitators is excluding the possibility that breeders attending a power struggle are trying to improve their own current position by dispersing secondarily. At one end of the spectrum was B♀︎5734 (PS10 and PS11). This bird bred at HORS in 2015 and 2016, but the group apparently failed to initiate a nest either year. Prior to the 2017 breeding season, B♀︎5734 was observed foraying and participating in power struggles at several territories. We therefore judged that she was likely prospecting for a superior breeding position and was a contender at these power struggles. Alternatively, B♂︎4051 attended PS9 with his son (H♂︎5658) from the prior year. After they won the power struggle, ♂︎5658 remained as the new breeder while ♂︎4051 returned home to BINO. In this case, B♂︎4051\u0026rsquo;s participation facilitated the successful dispersal of his son who, as a singleton, would have been unlikely to win the power struggle otherwise.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFacilitation and reciprocity\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOffspring acorn woodpeckers almost always help at the nest, a behavior that enhances reproductive success under most environmental conditions (Koenig et al. 2011b). Thus, when breeders assist helper dispersal by increasing the size of their coalition at a power struggle, they are reciprocating the help they received while breeding. The opposite of \u0026ldquo;pay-to-stay\u0026rdquo; (Kokko et al. 2002; Bergm\u0026uuml;ller and Taborsky 2005), helpers can be considered being repaid for their prior assistance. Sibling facilitation of offspring dispersal can also involve reciprocity. Birds that acquired a breeding position previously with the assistance of siblings may temporarily rejoin those same siblings to help compete as a coalition for a subsequent vacancy. By facilitating the dispersal of kin, such birds are also increasing the presence of relatives on the landscape, thereby providing opportunities for refuge (secondary dispersal) should a bird later lose its granary or be evicted from its territory. The clearest cases of reciprocity we documented are detailed in Table 4.\u003c/p\u003e\n\u003cp\u003eParental facilitation as envisioned by Brown (1987) encompassed three behaviors: (1) increased survival of offspring as a consequence of not being evicted from their home territory; (2) increased chance of achieving breeding status associated with using the home territory as a base from which to foray and search for reproductive vacancies; and (3) an increased possibility of inheriting and achieving breeding status on their home territory. All are potentially applicable to acorn woodpeckers (Barve et al. 2020a; Koenig et al. 2023b). Such behaviors are passive, only involving parents tolerating the presence of offspring. In contrast, the behaviors we describe here involve facilitators actively participating in coalitions that fight to fill a reproductive vacancy at a group to which their offspring or siblings will potentially disperse and subsequently breed. We are aware of no comparable behavior previously described in a cooperative breeder.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eParticipants in power struggles\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBased on an automated radio-telemetry system, Barve et al. (2020b) reported on the birds detected at three putative female power struggles. Of the birds detected, those that were considered candidates for potentially filling the vacancy (female helpers) were referred to as \u0026ldquo;warriors.\u0026rdquo; Breeder females and any males from other groups were referred to as \u0026ldquo;spectators,\u0026rdquo; since they either already had breeding status elsewhere or were presumed to be of the wrong sex to potentially fill the vacancy that initiated the power struggle. Birds identified as spectators spent an average of 52 min day\u003csup\u003e-1\u003c/sup\u003e at power struggles and were hypothesized to be gathering social information\u0026mdash;that is, gaining information about the group and other birds present at the power struggle. This hypothesis is consistent with the extensive knowledge that acorn woodpeckers apparently have about the social status of other individuals in the population (Pardo et al. 2018; 2020a; 2020b).\u003c/p\u003e\n\u003cp\u003eOur analyses here, based on behavioral observations, clarifies the motivation of many of the participants at power struggles that are not candidates to fill an initiating reproductive vacancy. Of 44 birds attending power struggles that were neither residents nor contenders, 30 (68%) were classified as either parental or sibling facilitators. The motivation of the remaining 14 (32%) nonresidents and noncontenders was apparently for a reason other than facilitating dispersal of kin. In some of these latter cases, birds may indeed be obtaining information, either of the territory where the power struggle took place or of other attendees at the power struggle. If so, the information being acquired, and how such information might eventually benefit them, remains to be determined.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFacilitation and fitness\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQuantifying the benefit of joining a coalition to enhance its competitiveness at a power struggle is difficult. Ideally, it would be necessary to know the success rate of different-sized coalitions, a value that is likely to differ depending on the season, population density, quality of the territory, and other factors, including the fitness consequences of breeding in coalitions\u0026mdash;which itself has proved challenging to determine (Mumme et al. 1988; Barve et al. 2021; Koenig et al. 2023a). Estimating the success rate of coalitions is likely to remain out of reach until it is possible to track the fate of birds emigrating out of the study area. Although current tracking technology has yielded insight on the foray behavior of acorn woodpeckers (Barve et al. 2020a), much remains to be done before it will be possible to resolve the dispersal-mortality confound of finite study areas such as ours (Koenig et al. 1996).\u003c/p\u003e\n\u003cp\u003ePower struggles are chaotic affairs involving a great deal of fighting and physical contact. It is not unusual for birds to fall to the ground, locked leg-to-leg in combat (Koenig 1981). We have observed occasional injuries, and birds participating in power struggles are clearly vulnerable to predation. Moreover, given that power struggles can start within minutes of a vacancy arising (Hannon et al. 1987), parental facilitators fighting elsewhere risk losing their own territory when leaving it undefended. There are thus significant costs to participating in power struggles. Facilitators apparently gain more than they risk by increasing the chances of close relatives gaining a reproductive opportunity, particularly if the relative has no other same-sex siblings and is thus unlikely to win a power struggle on its own. It is also possible, however, that facilitators do not fight as vigorously or spend as much time fighting as contenders that eventually gain a reproductive opportunity after winning a power struggle. We currently do not have data to examine this possibility.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo estimate inclusive fitness of social behaviors like breeding in coalitions, one needs to compare fitness when breeding singly (Koenig et al. 2023a). The difficulties in determining the costs and benefits of facilitation, however, render its inclusive fitness consequences unclear. Nonetheless, parental and sibling facilitation of dispersal provide yet another example of the importance of kin selection to the evolution of social behavior (Hamilton 1964a; 1964b).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003eWe thank the reviewers for comments and Hastings Reservation (DOI: 10.21973/N33Q0G) for hosting the project since its inception by Michael and Barbara MacRoberts in 1968. We especially wish to thank our colleagues and the 250+ field and assistants who have contributed to the project over the years.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e NDGH and ELW conceived the study; NDGH collected the observational data at the power struggles; all authors helped collect background data used to interpret results. WDK wrote the initial draft of the paper based in part on NDGH\u0026rsquo;s PhD thesis; all authors reviewed and edited subsequent drafts.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003eThis work was supported by the North American Bluebird Society and Sigma Xi Grants in Aid of Research to NDGH, National Science Foundation (NSF) grant IOS-1455881 to WDK, and NSF grant IOS-1455900 to ELW.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003eThis study was conducted under the auspices of the Animal Care and Use Committees of Old Dominion University (protocol 12-001 and 15-001), the University of California, Berkeley (protocol R010-0412), and Cornell University (protocol 2008-0185).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003eThe authors certify that they have no financial or non-financial competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003eAll data are available in the tables.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBarve S, Hagemeyer NDG, Winter RE, Chamberlain SD, Koenig WD, Winkler DW, Walters EL (2020a) Wandering woodpeckers: foray behavior in a social bird. Ecology 101:e02943\u003c/li\u003e\n\u003cli\u003eBarve S, Lahey AS, Brunner RM, Koenig WD, Walters EL (2020b) Tracking the warriors and spectators of acorn woodpecker wars. Curr Biol 30:R982-R983\u003c/li\u003e\n\u003cli\u003eBarve S, Riehl C, Walters EL, Haydock J, Dugdale HL, Koenig WD (2021) Lifetime reproductive benefits of cooperative polygamy vary for males and females in the acorn woodpecker (\u003cem\u003eMelanerpes formicivorus\u003c/em\u003e). Proc Roy Soc B 288:20210579\u003c/li\u003e\n\u003cli\u003eBergm\u0026uuml;ller R, Taborsky M (2005) Experimental manipulation of helping in a cooperative breeder: helpers \u0026lsquo;pay to stay\u0026rsquo; by pre-emptive appeasement. Anim Behav 69:19-28\u003c/li\u003e\n\u003cli\u003eBrown JL (1980) Fitness in complex avian social systems. In: Markl H (ed) Evolution of Social Behavior: Hypotheses and Empirical Tests. Verlag Chemie, Weinheim, pp 115-128\u003c/li\u003e\n\u003cli\u003eBrown JL (1987) Helping and Communal Breeding in Birds. Princeton Univ Press, Princeton, NJ\u003c/li\u003e\n\u003cli\u003eChiarati E, Canestrari D, Vila M, Vera R, Baglione V (2011) Nepotistic access to food resources in cooperatively breeding carrion crows. Behav Ecol Sociobiol 65:1791-1800\u003c/li\u003e\n\u003cli\u003eCockburn A (1998) Evolution of helping behavior in cooperatively breeding birds. Annu Rev Ecol Syst 29:141-177\u003c/li\u003e\n\u003cli\u003eCusick JA, de Villa M, DuVal EH, Cox JA (2018) How do helpers help? Helper contributions throughout the nesting cycle in the cooperatively breeding brown-headed nuthatch. Behav Ecol Sociobiol 72:43\u003c/li\u003e\n\u003cli\u003eDickinson JL, Hatchwell BJ (2004) Fitness consequences of helping. In: Koenig WD, Dickinson JL (eds) Ecology and Evolution of Cooperative Breeding in Birds. Cambridge Univ Press, Cambridge, U.K., pp 48-66\u003c/li\u003e\n\u003cli\u003eDickinson JL, Haydock J, Koenig WD, Stanback MT, Pitelka FA (1995) Genetic monogamy in single-male groups of acorn woodpeckers, \u003cem\u003eMelanerpes formicivorus\u003c/em\u003e. Mol Ecol 4:765-769\u003c/li\u003e\n\u003cli\u003eEikenaar C, Richardson DS, Brouwer L, Komdeur J (2007) Parent presence, delayed dispersal, and territory acquisition in the Seychelles warbler. Behav Ecol 18:874-879\u003c/li\u003e\n\u003cli\u003eEkman J, Bylin A, Tegelstr\u0026ouml;m H (2000) Parental nepotism enhances survival of retained offspring in the Siberian jay. Behav Ecol 11:416-420\u003c/li\u003e\n\u003cli\u003eEkman J, Dickinson JL, Hatchwell BJ, Griesser M (2004) Delayed dispersal. In: Koenig WD, Dickinson JL (eds) Ecology and Evolution of Cooperative Breeding in Birds. Cambridge Univ Press, Cambridge, UK, pp 35-47\u003c/li\u003e\n\u003cli\u003eGriffin JR (1974) Botanical resources of the Hastings Reservation, Monterey County, California. Madro\u0026ntilde;o 22:329-332\u003c/li\u003e\n\u003cli\u003eHamilton WD (1964a) The genetical evolution of social behaviour. I. J Theor Biol 7:1-16\u003c/li\u003e\n\u003cli\u003eHamilton WD (1964b) The genetical evolution of social behaviour. II. J Theor Biol 7:17-52\u003c/li\u003e\n\u003cli\u003eHannon SJ, Mumme RL, Koenig WD, Pitelka FA (1985) Replacement of breeders and within-group conflict in the cooperatively breeding acorn woodpecker. Behav Ecol Sociobiol 17:303-312\u003c/li\u003e\n\u003cli\u003eKoenig WD (1981) Space competition in the acorn woodpecker: power struggles in a cooperative breeder. Anim Behav 29:396-409\u003c/li\u003e\n\u003cli\u003eKoenig WD, Dickinson JL (2016) Cooperative Breeding in Vertebrates: Studies in Ecology, Evolution and Behavior. Cambridge Univ Press, Cambridge, UK\u003c/li\u003e\n\u003cli\u003eKoenig WD, Mumme RL (1987) Population Ecology of the Cooperatively Breeding Acorn Woodpecker. Princeton Univ Press, Princeton, NJ\u003c/li\u003e\n\u003cli\u003eKoenig WD, Van Vuren D, Hooge PN (1996) Detectability, philopatry, and the distribution of dispersal distances in vertebrates. Trends Ecol Evol 11:514-517\u003c/li\u003e\n\u003cli\u003eKoenig WD, Haydock J, Stanback MT (1998) Reproductive roles in the cooperatively breeding acorn woodpecker: incest avoidance versus reproductive competition. Am Nat 151:243-255\u003c/li\u003e\n\u003cli\u003eKoenig WD, Stanback MT, Haydock J (1999) Demographic consequences of incest avoidance in the cooperatively breeding acorn woodpecker. Anim Behav 57:1287-1293\u003c/li\u003e\n\u003cli\u003eKoenig WD, Hooge PN, Stanback MT, Haydock J (2000) Natal dispersal in the cooperatively breeding acorn woodpecker. Condor 102:492-502\u003c/li\u003e\n\u003cli\u003eKoenig WD, Walters EL, Haydock J (2011a) Fitness consequences of within-brood dominance in the cooperatively breeding acorn woodpecker. Behav Ecol Sociobiol 65:2229-2238\u003c/li\u003e\n\u003cli\u003eKoenig WD, Walters EL, Haydock J (2011b) Variable helper effects, ecological conditions, and the evolution of cooperative breeding in the acorn woodpecker. Am Nat 178:145-158\u003c/li\u003e\n\u003cli\u003eKoenig WD, Walters EL, Haydock J (2016) Acorn woodpeckers: helping at the nest, polygynandry, and dependence on a variable acorn crop. In: Koenig WD, Dickinson JL (eds) Cooperative Breeding in Vertebrates: Studies of Ecology, Evolution, and Behavior Cambridge Univ Press, Cambridge, UK, pp 217-236\u003c/li\u003e\n\u003cli\u003eKoenig WD, Walters EL, Stacey PB, Stanback MT, Mumme RL (2020) Acorn woodpecker (\u003cem\u003eMelanerpes formicivorus\u003c/em\u003e), version 1.0. In: Rodewald PG, Keeney BK (eds) Birds of the World. Cornell Lab of Ornithology, Ithaca, NY, USA \u003c/li\u003e\n\u003cli\u003eKoenig WD, Barve S, Haydock J, Dugdale HL, Oli MK, Walters EL (2023a) Lifetime inclusive fitness effects of cooperative polygamy in the acorn woodpecker. Proc Nat Acad Sci (USA) 120:e2219345120\u003c/li\u003e\n\u003cli\u003eKoenig WD, Haydock J, Dugdale HL, Walters EL (2023b) Territory inheritance and the evolution of cooperative breeding in the acorn woodpecker. Anim Behav (in press). \u003c/li\u003e\n\u003cli\u003eKokko H, Johnstone RA, Wright J (2002) The evolution of parental and alloparental effort in cooperatively breeding groups: when should helpers pay to stay? Behav Ecol 13:291-300\u003c/li\u003e\n\u003cli\u003eMacRoberts MH, MacRoberts BR (1976) Social organization and behavior of the acorn woodpecker in central coastal California. Ornith Monogr 21:1-115\u003c/li\u003e\n\u003cli\u003eMumme RL (1992) Do helpers increase reproductive success? An experimental analysis in the Florida scrub jay. Behav Ecol Sociobiol 31:319-328\u003c/li\u003e\n\u003cli\u003eMumme RL, Koenig WD, Pitelka FA (1988) Costs and benefits of joint nesting in the acorn woodpecker. Am Nat 131:654-677\u003c/li\u003e\n\u003cli\u003ePardo M, Sparks EA, Kuray TS, Hagemeyer NDG, Walters EL, Koenig WD (2018) Wild acorn woodpeckers recognize associations between individuals in other groups. Proc Roy Soc B 285:20181017\u003c/li\u003e\n\u003cli\u003ePardo M, Hayes CE, Walters EL, Koenig WD (2020a) Acorn woodpeckers vocally discriminate current and former group members from non-group members. Behav Ecol 31:1120-1128\u003c/li\u003e\n\u003cli\u003ePardo M, Walters EL, Koenig WD (2020b) Experimental evidence that acorn woodpeckers recognize relationships among third parties no longer living. Behav Ecol 31:1257-1265\u003c/li\u003e\n\u003cli\u003eRiehl C (2013) Evolutionary routes to non-kin cooperative breeding in birds. Proc Roy Soc B 280:20132245\u003c/li\u003e\n\u003cli\u003eStanback MT, Koenig WD (1994) Techniques for capturing birds inside natural cavities. J Field Ornithol 65:70-75\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Summary of power struggles (PS) monitored for this study\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003ePS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003eDates\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003eOriginal cause\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eResult\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003eComments\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e11\u0026ndash;12 Aug 2013\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eCAVI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♀︎ vacancy combined with temporary capture of 2 of the 3\u0026nbsp;♂︎♂︎\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003e♀︎ vacancy filled by a\u0026nbsp;♀︎ from PLQE;\u0026nbsp;♂︎♂︎ evicted and replaced by a coalition of 3\u0026nbsp;♂︎♂︎ from BLMP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003e♀︎had been gone for some time, but the PS started following 2 of the\u0026nbsp;♂︎♂︎ being captured and held temporarily for processing; the\u0026nbsp;♂︎♂︎ were subsequently driven out by a large coalition from group BLMP (one of which had previously moved to MISH)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e30 Mar \u0026amp; 2 May 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eJAIM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♀︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eFilled by a\u0026nbsp;♀︎ from KNOL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003e♀︎ replaced in March; fighting resumed into May but did not lead to further change in group composition\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e7 Mar 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eROBH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♀︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eFilled by a coalition of 2\u0026nbsp;♀︎♀︎ from CAVI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e25 Mar \u0026amp; 2 May 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003ePLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♂︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eEntire group evicted and replaced\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003eTerritory taken over by UPBA group and forced into an adjacent territory\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e18\u0026ndash;25 Mar 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eKNOL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♀︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eFilled by a coalition of 3\u0026nbsp;♀︎♀︎ from PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e14\u0026ndash;15 May 2014\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eLHAY\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♂︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003e♀︎ breeder evicted, replaced by coalition of 2\u0026nbsp;♀︎♀︎\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003eWith new\u0026nbsp;♀︎♀︎, the 2 helper\u0026nbsp;♂︎♂︎ in the group inherited and became breeders\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e8 Apr 2015\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eUPBA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003eVacant territory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eNew group\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003eColonized by a coalition of 2\u0026nbsp;♂︎♂︎ from PLQE and a\u0026nbsp;♀︎ from CABI\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e2\u0026ndash;4 Apr 2016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eA1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♀︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eFilled by a coalition of 3\u0026nbsp;♀︎♀︎ from KOUT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e3\u0026ndash;4 Apr 2016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003eRE10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003eVacant territory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eNew group\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003eColonized by a\u0026nbsp;♂︎ from BINO and a coalition of 2 NOBA\u0026nbsp;♀︎♀︎\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003eMar\u0026ndash;Aug 2017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003ePLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e♀︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003eEventually filled by a coalition of 4\u0026nbsp;♀︎♀︎ from JAIM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003ePS continued intermittently for months\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.123711340206185%\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.402061855670103%\"\u003e\n \u003cp\u003e5\u0026ndash;6 Aug 2017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.24742268041237%\"\u003e\n \u003cp\u003e1800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003eNo initial vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.49484536082474%\"\u003e\n \u003cp\u003e♂︎ replaced by a coalition of 2 NOBA\u0026nbsp;♂︎♂︎\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"42.2680412371134%\"\u003e\n \u003cp\u003eStarted with\u0026nbsp;♀︎♀︎ fighting but after several days the breeder\u0026nbsp;♂︎ disappeared\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u0026nbsp;\u003c/strong\u003eSummary of the apparent causes of power struggles monitored for this study and reported by Koenig (1981) and Hannon et al. (1985); excluded are power struggles of unknown origin and those initiated by experimental removals\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"96%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\"\u003e\n \u003cp\u003eApparent cause\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.61855670103093%\"\u003e\n \u003cp\u003eThis study\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003eKoenig (1981)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003eHannon et al. (1985)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\"\u003e\n \u003cp\u003e♀︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.61855670103093%\"\u003e\n \u003cp\u003e5 (45%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e7 (47%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e3 (50%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e15 (47%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\"\u003e\n \u003cp\u003e♂︎ vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.61855670103093%\"\u003e\n \u003cp\u003e2 (18%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e5 (33%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e3 (50%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e10 (31%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\"\u003e\n \u003cp\u003eVacancy of both sexes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.61855670103093%\"\u003e\n \u003cp\u003e1 (9%)\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e1 (3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\"\u003e\n \u003cp\u003eVacant territory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.61855670103093%\"\u003e\n \u003cp\u003e2 (18%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e2 (6%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\"\u003e\n \u003cp\u003eNo initial vacancy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.61855670103093%\"\u003e\n \u003cp\u003e1 (9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e3 (20%)\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e4 (13%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.711340206185568%\"\u003e\n \u003cp\u003e\u003cem\u003eN\u003c/em\u003e power struggles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.61855670103093%\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e32\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u0026nbsp;\u003c/sup\u003eIncludes PS1 (Table 1), where there was a female vacancy but the power struggle started following the capture of two of the three males for unrelated reasons.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u0026nbsp;\u003c/sup\u003eIn two of these three cases there was no change in group composition, while in the third the entire group was expelled.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u0026nbsp;\u003c/strong\u003eBanded acorn woodpeckers observed at the power struggles monitored for this study and their apparent motivation for attendance\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\"\u003e\n \u003cp\u003ePS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\"\u003e\n \u003cp\u003eGroup\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\"\u003e\n \u003cp\u003eResidents\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003eContenders\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\"\u003e\n \u003cp\u003eFacilitators\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\"\u003e\n \u003cp\u003eOthers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003eNotes\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eCAVI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎3165x\u003c/p\u003e\n \u003cp\u003eB♂︎3284x\u003c/p\u003e\n \u003cp\u003eH♂︎5094x\u003c/p\u003e\n \u003cp\u003eH♂︎5378x\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4621 (BLMP)\u003c/p\u003e\n \u003cp\u003eH♂︎4933 (BLMP)\u003c/p\u003e\n \u003cp\u003eH♂︎4935 (BLMP)\u003c/p\u003e\n \u003cp\u003eH♂︎5278 (SHIL)\u003c/p\u003e\n \u003cp\u003eH♀︎5151 (PLQE)\u003c/p\u003e\n \u003cp\u003eH♀︎5325 (CABI)\u003c/p\u003e\n \u003cp\u003eH♀︎5390 (PLQE)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♂︎5376s (BLMP)\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5377s (BLMP)\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5007s (PLQE)\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5079s (PLQE)\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5389s (PLQE)\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eB♀︎4938 (JAIM)\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e1\u003c/sup\u003eThese were all siblings of the birds that displaced the residents but returned home rather than remain at CAVI at the conclusion of the PS.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e2\u003c/sup\u003eB♀︎4938 was observed at CAVI taking acorns from the granary to her home group JAIM, which was adjacent to CAVI.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eJAIM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4890\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♀︎5103 (KNOL)\u003c/p\u003e\n \u003cp\u003eB♀︎4854 (UPBA)\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎4470 (SHIL)\u003c/p\u003e\n \u003cp\u003eH♀︎5091 (SHW)\u003c/p\u003e\n \u003cp\u003eH♀︎5430 (PIPE)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e3\u003c/sup\u003eB♀︎4854 was involved in PSs at JAIM (PS2) and at PLQE (PS4), territories very close to each other where PSs occurred nearly simultaneously. Her involvement at PS2 may have been secondary to the one at PLQE (where she ultimately moved), but she was apparently prospecting to leave UPBA and thus categorized as a \u003cem\u003econtender\u003c/em\u003e.\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eROBH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4884\u003c/p\u003e\n \u003cp\u003eB♂︎5220\u003c/p\u003e\n \u003cp\u003eH♂︎5583inh\u003c/p\u003e\n \u003cp\u003eH♂︎5585inh\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♀︎5390 (CAVI)\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♀︎5079s (PLQE)\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎5151s (CAVI)\u003csup\u003e4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e4\u003c/sup\u003e B♀︎5390 stayed at CAVI following PS1 but moved here after being facilitated by two of her sisters, H♀︎5079 (still at group PLQE) and B♀︎5151, her sister who had moved with her to group CAVI following PS1.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003ePLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eH♂︎5152x\u003c/p\u003e\n \u003cp\u003eH♂︎5153x\u003c/p\u003e\n \u003cp\u003eB♀︎4629x\u003c/p\u003e\n \u003cp\u003eH♀︎5151x\u003c/p\u003e\n \u003cp\u003eH♀︎5389x\u003c/p\u003e\n \u003cp\u003eH♀︎5482x\u003c/p\u003e\n \u003cp\u003eH♀︎5486x\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎5006 (UPBA)\u003c/p\u003e\n \u003cp\u003eH♂︎5303 (DIPS)\u003c/p\u003e\n \u003cp\u003eH♂︎5474 (DIPS)\u003c/p\u003e\n \u003cp\u003eH♂︎5454 (PLAN)\u003c/p\u003e\n \u003cp\u003eB♀︎4854 (UPBA)\u003c/p\u003e\n \u003cp\u003eB♀︎5014 (UPBA)\u003c/p\u003e\n \u003cp\u003eH♀︎5317 (CHIM)\u003c/p\u003e\n \u003cp\u003eH♀︎5370 (SHIL)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4890 (JAIM)\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎5103 (JAIM)\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e5\u003c/sup\u003eB♂︎4890 had been a successful breeder at JAIM for over 2 years, while B♀︎5103 had recently moved to JAIM (PS2) and remained there until 2017. Thus neither bird was likely to be prospecting, nor did they have offspring whose dispersal they might have been facilitating. Also, JAIM is adjacent to PLQE, making it likely they were defending their own territory or drawn into the PS for some other reason.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eKNOL\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎3399\u003c/p\u003e\n \u003cp\u003eB♂︎3753\u003c/p\u003e\n \u003cp\u003eB♂︎5059\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♀︎5007 (PLQE)\u003c/p\u003e\n \u003cp\u003eH♀︎5079 (PLQE)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; ♀︎NOBA (PLQE)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♀︎5151s (CAVI)\u003csup\u003e6\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5389s (PLQE)\u003c/p\u003e\n \u003cp\u003eH♀︎5482s (PLQE)\u003c/p\u003e\n \u003cp\u003eH♀︎5486s (PLQE)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e♂︎5204 (HORS)\u003csup\u003e7\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e6\u003c/sup\u003eB♀︎5151 had previously moved to CAVI but was born at PLQE and a sister of the 3 PLQE ♀︎♀︎ that remained (including the ♀︎NOBA, who was presumably from a missed nest).\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e7\u003c/sup\u003e♂︎5204 had not been seen since leaving his home group early in 2013. As a ♂︎ at what was an unambiguous ♀︎PS with no known relatives whose dispersal he might have been facilitating, we classified him as \u003cem\u003eother\u003c/em\u003e.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eLHAY\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eH♂︎4928inh\u003c/p\u003e\n \u003cp\u003eH♂︎5251inh\u003c/p\u003e\n \u003cp\u003eB♀︎4570x\u003c/p\u003e\n \u003cp\u003eB♀︎4590x\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♀︎5476 (DIPS)\u003c/p\u003e\n \u003cp\u003eH♀︎5247 (BLM2)\u003c/p\u003e\n \u003cp\u003eH♀︎5140 (HORS)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎5250s (BRWN)\u003csup\u003e8\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5202s (HORS)\u003c/p\u003e\n \u003cp\u003eH♂︎5207s (HORS)\u003c/p\u003e\n \u003cp\u003eH♂︎5416s (HORS)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e8\u003c/sup\u003eB♂︎5250 had previously moved to BRWN but was born at LHAY and was thus a sibling of the two helper ♂︎residents, H♂︎4928 and H♂︎5251. He therefore was presumably helping them defend the territory against intruders and was considered a \u003cem\u003esibling facilitator\u003c/em\u003e. He later switched territories and returned home to LHAY, joining H♂︎5251 (now B♂︎5251) as a cobreeder.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eUPBA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♂︎5562 (PLQE)\u003c/p\u003e\n \u003cp\u003eH♂︎5698 (PLQE)\u003c/p\u003e\n \u003cp\u003eH♀︎4904 (CABI)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎5006p (PLQE)\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♂︎5153p (PLQE)\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5700s (PLQE)\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5701s (PLQE)\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎4854p (PLQE)\u003csup\u003e9\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e9\u003c/sup\u003eThese birds returned to PLQE following the PS, and thus were all considered \u003cem\u003efacilitators\u003c/em\u003e of the 2 helpers that remained.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eA1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4561\u003c/p\u003e\n \u003cp\u003eH♂︎5750inh\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♀︎5309 (KOUT)\u003c/p\u003e\n \u003cp\u003eH♀︎5642 (KOUT)\u003c/p\u003e\n \u003cp\u003eH♀︎5740 (KOUT)\u003c/p\u003e\n \u003cp\u003eB♀︎5155 (LAMB)\u003csup\u003e10\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5349 (BKOK)\u003c/p\u003e\n \u003cp\u003eH♀︎5383 (LA2)\u003c/p\u003e\n \u003cp\u003eH♀︎5465 (LA2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♀︎5741s (KOUT)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4568 (UA2)\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5265 (UA2)\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5658 (BINO)\u003csup\u003e11\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e\u0026nbsp;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e10\u003c/sup\u003eB♀︎5155 had previously inherited breeder status at LAMB in late 2015. However, the group did not appear to have bred in 2016 and thus B♀︎5155 is considered a \u003cem\u003econtender\u003c/em\u003e potentially prospecting for a new group.\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e11\u003c/sup\u003eThese 3 males from nearby groups had no known ♀︎♀︎ relatives participating in this ♀︎PS, and may have been defending their own territories. We thus classified them as \u003cem\u003eothers\u003c/em\u003e.\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eRE10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♂︎5658 (BINO)\u003c/p\u003e\n \u003cp\u003eH♂︎5739 (KOUT)\u003csup\u003e13\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e2 NOBA\u0026nbsp;♀︎♀︎\u0026nbsp;(UNK)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4051p (BINO)\u003csup\u003e12\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5825s (KOUT)\u003csup\u003e13\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e12\u003c/sup\u003eB♂︎4051 fought at this PS as a \u003cem\u003eparental facilitator\u003c/em\u003e of H♂︎5658, his son from 2015.\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e13\u003c/sup\u003eH♂︎5739 and H♀︎5825 were siblings that both participated in the PS. Since RE10 had been vacant, either, but not both, could have remained and bred had they won (which they did not). We therefore classified one of them (H♂︎5739, who was older) as a \u003cem\u003econtender\u003c/em\u003e and H♀︎5825 as a \u003cem\u003esibling facilitator\u003c/em\u003e.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003ePLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎5006\u003c/p\u003e\n \u003cp\u003eB♂︎5152\u003c/p\u003e\n \u003cp\u003eB♂︎5153\u003c/p\u003e\n \u003cp\u003eH♂︎5878\u003c/p\u003e\n \u003cp\u003eH♀︎5876x\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♀︎5103 (JAIM)\u003c/p\u003e\n \u003cp\u003eH♀︎5944 (JAIM)\u003c/p\u003e\n \u003cp\u003eH♀︎5945 (JAIM)\u003c/p\u003e\n \u003cp\u003eH♀︎5946 (JAIM)\u003c/p\u003e\n \u003cp\u003eB♀︎4713 (BUCK)\u003csup\u003e14\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5192 (PIPE)\u003c/p\u003e\n \u003cp\u003eH♀︎5498 (CECN)\u003c/p\u003e\n \u003cp\u003eH♀︎5715 (KNOL)\u003c/p\u003e\n \u003cp\u003eB♀︎5734 (HORS)\u003csup\u003e15\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5771 (1500)\u003c/p\u003e\n \u003cp\u003eH♀︎5912 (LOLF)\u003c/p\u003e\n \u003cp\u003eB♀︎6001 (CABI)\u003csup\u003e16\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5970 (CABI)\u003csup\u003e16\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5972 (MACR)\u003c/p\u003e\n \u003cp\u003eH♀︎5903 (PLAN)\u003c/p\u003e\n \u003cp\u003eH♀︎5938 (Y)\u003c/p\u003e\n \u003cp\u003eH♀︎5950 (UPBA)\u003c/p\u003e\n \u003cp\u003eH♀︎5954 (CHIM)\u003c/p\u003e\n \u003cp\u003eH♀︎5955 (CHIM)\u003c/p\u003e\n \u003cp\u003eH♀︎5979 (ROBH)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp;♀︎6005 (UNK)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eH♂︎6002s (CHIM)\u003csup\u003e17\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5891s (JAIM)\u003c/p\u003e\n \u003cp\u003eB♂︎5698p (UPBA)\u003csup\u003e18\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5952s (UPBA)\u003csup\u003e18\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎4904p (UPBA)\u003csup\u003e18\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003eH♂︎5880 (CAVI)\u003csup\u003e19\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♂︎5881 (CAVI)\u003csup\u003e19\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎4629 (CAVI)\u003csup\u003e19\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎4493 (FNCH)\u003csup\u003e20\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎4968 (RE03)\u003csup\u003e21\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎5209\u0026nbsp;(AMAD)\u003csup\u003e21\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎5659 (MIKE)\u003csup\u003e22\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e14\u003c/sup\u003eAlthough B♀︎4713 had been a breeder at BUCK since 2013, she apparently left the group after the long-time breeder ♂︎disappeared in early 2016. Thus, we considered her a \u003cem\u003econtender\u003c/em\u003e interested in switching territories.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e15\u003c/sup\u003eB♀︎5734 bred at HORS in 2015 and 2016, but the group failed to initiate a nest either year. By 2017 she was foraying, presumably in search of a new breeding opportunity, and thus we considered her a \u003cem\u003econtender\u003c/em\u003e both here and at PS11.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e16\u003c/sup\u003eAt the time of this PS, CABI had no breeder ♂︎. Thus, although B♀︎6001 was apparently the breeder ♀︎at CABI, we assumed she was prospecting for a new territory and considered her a \u003cem\u003econtender\u003c/em\u003e along with her daughter H♀︎5970.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e17\u003c/sup\u003eThe origin of H♂︎6002 (banded at CHIM early in 2017) was unclear, but he was thought to be from a missed nest, and thus a sibling of H♀︎5954 and H♀︎5955. We thus classified him as a \u003cem\u003esibling facilitator\u003c/em\u003e.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e18\u003c/sup\u003eBoth B♂︎5698 and B♀︎4904 bred at UPBA in 2017 and 2018 and were thus assumed to be \u003cem\u003eparental facilitators\u003c/em\u003e of H♀︎5950, their daughter from 2016. Since this was a ♀︎ vacancy, we classified H♂︎5952 as a \u003cem\u003esibling facilitator\u003c/em\u003e of his sister, H♀︎5950.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e19\u003c/sup\u003eThese three birds were from the adjacent CAVI territory that did not contain any helper ♀︎♀︎ observed at the PS. Further, B♀︎4629 bred successfully at CAVI in both 2015 and 2016 and was still breeding there as of 2022. We thus classified them as \u003cem\u003eother\u003c/em\u003e.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e20\u003c/sup\u003eB♀︎4493 was a long-time breeder at her home group (FNCH) and was considered unlikely to be prospecting for a new territory. Group FNCH, however, contained one helper ♀, who was not seen at the PS. We thus considered her \u003cem\u003eother\u003c/em\u003e, but it is possible that the helper ♀ was missed and that B♀︎4493 was a \u003cem\u003eparental facilitator\u003c/em\u003e.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e21\u003c/sup\u003eFemales B♀︎4968, and B♀︎5209 were long-time breeders at their home groups and were judged unlikely to be interested in switching territories. Neither of their home groups contained a helper ♀︎ who might have competed at the PS, and thus we considered them \u003cem\u003eothers\u003c/em\u003e.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e22\u003c/sup\u003eB♀︎5659 inherited her natal territory (MIKE) in Sept. 2016 and bred there in 2017 after the conclusion of this PS. There was no helper ♀︎♀︎ at MIKE in 2017, and we thus considered her \u003cem\u003eother\u003c/em\u003e.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"4.166666666666667%\" valign=\"top\"\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.333333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e1800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.416666666666666%\" valign=\"top\"\u003e\n \u003cp\u003eB♂︎4589x\u003c/p\u003e\n \u003cp\u003eB♀︎4261\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003e♂︎6069 (UNK)\u003c/p\u003e\n \u003cp\u003e♂︎NOBA (UNK)\u003c/p\u003e\n \u003cp\u003eH♀︎5636 (1500)\u003c/p\u003e\n \u003cp\u003eH♀︎5771 (1500)\u003c/p\u003e\n \u003cp\u003eH♀︎5774 (1500)\u003c/p\u003e\n \u003cp\u003eB♀︎5734 (HORS)\u003csup\u003e15\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eH♀︎5763 (1600)\u003c/p\u003e\n \u003cp\u003eH♀︎5855 (1600)\u003c/p\u003e\n \u003cp\u003eH♀︎5866 (SOSP)\u003c/p\u003e\n \u003cp\u003eH♀︎5712 (SHIL)\u003c/p\u003e\n \u003cp\u003eH♀︎5990 (SHIL)\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.625%\" valign=\"top\"\u003e\n \u003cp\u003eB♀︎4672p (1500)\u003csup\u003e23\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eB♀︎5813p (SOSP)\u003csup\u003e23\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.583333333333334%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"31.25%\" valign=\"top\"\u003e\n \u003cp\u003e\u003csup\u003e15\u003c/sup\u003eSee PS10.\u003c/p\u003e\n \u003cp\u003e\u003csup\u003e23\u003c/sup\u003eThese 2 ♀︎♀︎ were breeders in their home groups in 2016 and 2017 and were likely present at this PS as \u003cem\u003eparental facilitators\u003c/em\u003e of their daughters (H♀︎5636, H♀︎5771, and H♀︎5774 from group 1500 and H♀︎5866 from group SOSP, respectively).\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eBirds winning the power struggle and remaining in the territory are highlighted. B=breeder; H=helper; 4-letter code in parentheses is the group from which the bird originated; PS numbers refer to power struggles in Table 1; \u0026ldquo;x\u0026rdquo; indicates a bird leaving or being evicted from the group; \u0026ldquo;s\u0026rdquo; indicates a sibling facilitator; \u0026ldquo;p\u0026rdquo; a parental facilitator; \u0026ldquo;inh\u0026rdquo; indicates a bird that inherited the territory following the power struggle. NOBA = unbanded bird; UNK = unknown group.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u0026nbsp;\u003c/strong\u003eHistories of seven helper female siblings from group PLQE at three power struggles in 2013 and 2014, all of which they won\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"648\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eBird\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003eYear fledged\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003ePS1: CAVI (2013)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003ePS3: ROBH (2014)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003ePS5: KNOL (2014)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eH♀5007\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003e2010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eReturned to PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eStayed\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eH♀5079\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003e2011\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eReturned to PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003eReturned to PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eStayed\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eH♀5151\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003e2012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eStayed\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003eReturned to CAVI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eReturned to CAVI\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eH♀5389\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003e2012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eReturned to PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eReturned to PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eH♀5390\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003e2012\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eStayed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003eStayed\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eH♀5482\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003e2013\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eReturned to PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"13.88888888888889%\"\u003e\n \u003cp\u003eH♀5486\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.037037037037036%\"\u003e\n \u003cp\u003e2013\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.925925925925927%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"24.074074074074073%\"\u003e\n \u003cp\u003eReturned to PLQE\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eEmpty cells designate birds not observed at the power struggle (either not present or not alive).\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5\u0026nbsp;\u003c/strong\u003eSummary of attendees at power struggles (excluding residents)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"36.633663366336634%\"\u003e\n \u003cp\u003eCategory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.792079207920793%\"\u003e\n \u003cp\u003eMales\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.762376237623762%\"\u003e\n \u003cp\u003eFemales\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.81188118811881%\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"36.633663366336634%\"\u003e\n \u003cp\u003eContenders\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.792079207920793%\"\u003e\n \u003cp\u003e14 (39%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.762376237623762%\"\u003e\n \u003cp\u003e59 (73%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.81188118811881%\"\u003e\n \u003cp\u003e73 (62%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"36.633663366336634%\"\u003e\n \u003cp\u003eParental facilitators\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.792079207920793%\"\u003e\n \u003cp\u003e4 (11%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.762376237623762%\"\u003e\n \u003cp\u003e4 (5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.81188118811881%\"\u003e\n \u003cp\u003e8 (7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"36.633663366336634%\"\u003e\n \u003cp\u003eSibling facilitators\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.792079207920793%\"\u003e\n \u003cp\u003e11 (31%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.762376237623762%\"\u003e\n \u003cp\u003e11 (14%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.81188118811881%\"\u003e\n \u003cp\u003e22 (19%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"36.633663366336634%\"\u003e\n \u003cp\u003eOthers\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.792079207920793%\"\u003e\n \u003cp\u003e7 (19%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.762376237623762%\"\u003e\n \u003cp\u003e7 (9%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.81188118811881%\"\u003e\n \u003cp\u003e14 (12%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"36.633663366336634%\"\u003e\n \u003cp\u003e\u003cem\u003eN\u003c/em\u003e birds\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"20.792079207920793%\"\u003e\n \u003cp\u003e36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"23.762376237623762%\"\u003e\n \u003cp\u003e81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.81188118811881%\"\u003e\n \u003cp\u003e117\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"behavioral-ecology-and-sociobiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"beas","sideBox":"Learn more about [Behavioral Ecology and Sociobiology](http://link.springer.com/journal/265)","snPcode":"265","submissionUrl":"https://www.editorialmanager.com/beas/default.aspx","title":"Behavioral Ecology and Sociobiology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"acorn woodpecker, cooperative breeding, dispersal facilitation, nepotism, parental facilitation, reciprocity","lastPublishedDoi":"10.21203/rs.3.rs-3873292/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3873292/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Offspring that delay dispersal in cooperatively breeding species have been hypothesized to gain direct fitness benefits via parental facilitation—being passively tolerated on their natal territory by their parents—thereby enjoying enhanced survival and increased probability of acquiring a breeding position in the population. Here we describe active facilitation in the acorn woodpecker (Melanerpes formicivorus) by parents and siblings assisting the dispersal of helpers in their social group. Helpers in this species compete for reproductive opportunities in “power struggles” that take place when breeders of one sex die or disappear, thereby creating a reproductive vacancy. Individuals compete at power struggles in coalitions of relatives, in which larger coalitions are more likely to be victorious. Based on observations of banded birds, we found that an estimated 26% of individuals competing as part of a winning coalition at a power struggle returned to their home territory at its conclusion, suggesting that they were facilitating the dispersal of kin (generally parents or siblings) that stayed to become breeders on the new territory. In at least one group, parental and sibling facilitation was reciprocated; that is, a bird that was helped at a power struggle by a relative joined that same relative as part of a coalition at a subsequent power struggle. Dispersal facilitation is a novel means by which parents can enhance the direct fitness of offspring or siblings can enhance each other’s inclusive fitness in this highly social species.","manuscriptTitle":"Active facilitation of helper dispersal by parents and siblings in the cooperatively breeding acorn woodpecker","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-06 11:17:00","doi":"10.21203/rs.3.rs-3873292/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revisions Needed","date":"2024-06-23T05:53:40+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-02-08T07:49:55+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-02-04T08:17:58+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-24T16:29:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"Behavioral Ecology and Sociobiology","date":"2024-01-20T15:26:42+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"behavioral-ecology-and-sociobiology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"beas","sideBox":"Learn more about [Behavioral Ecology and Sociobiology](http://link.springer.com/journal/265)","snPcode":"265","submissionUrl":"https://www.editorialmanager.com/beas/default.aspx","title":"Behavioral Ecology and Sociobiology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f59dcfe4-b404-4585-9ec4-2f174a878ad6","owner":[],"postedDate":"February 6th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-12T16:02:47+00:00","versionOfRecord":{"articleIdentity":"rs-3873292","link":"https://doi.org/10.1007/s00265-024-03505-z","journal":{"identity":"behavioral-ecology-and-sociobiology","isVorOnly":false,"title":"Behavioral Ecology and Sociobiology"},"publishedOn":"2024-08-06 15:57:33","publishedOnDateReadable":"August 6th, 2024"},"versionCreatedAt":"2024-02-06 11:17:00","video":"","vorDoi":"10.1007/s00265-024-03505-z","vorDoiUrl":"https://doi.org/10.1007/s00265-024-03505-z","workflowStages":[]},"version":"v1","identity":"rs-3873292","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3873292","identity":"rs-3873292","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}