Nesting biology, growth and survival of the Slender-Billed Inezia: Insights into the life history of the South America’s smallest passerine

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This species is endemic to the lowlands of northwestern Venezuela and northeastern Colombia, where it inhabits seasonal dry and hot environments. Until now, little was known about its reproductive biology. In this study, we described and evaluate key aspects of the nesting biology of I. tenuirostris . To achieve this, we monitored 43 nests located in forest patches within a very dry forest in an early successional stage. The nests were tiny “ventilated” cups constructed from fine woody stems. Clutch size consisted of two immaculate white eggs, which were incubated for an average of 12.5 days. At hatching, nestlings had black skin with sparse whitish down on the dorsal area and fledged after 11.6 days. The growth rate of the nestlings K was 0.42, with the maximum growth rate occurring after 3.73 days post-hatching, reaching 0.49 grams/day. Survival analysis revealed a sharp decline in nest survival during incubation (a 47% reduction) and a steady decline during chick-rearing (a 23% reduction), resulting in an overall low nesting survival rate of 30%. Our findings suggest potentially intriguing adaptations in I. tenuirostris for surviving in harsh environments, including: (1) the ventilated cup-shaped nest, which likely reduces water absorption and/or mitigates overheating; (2) the black skin of nestlings, which may provide photoprotection against harmful UV radiation; and (3) the accelerated growth rate of nestlings is potentially an evolutionary response to the persistent risk of nest predation. nest design reproductive success neotropics life-history tropical dry forest predation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The neotropics are renowned for their rich and unique avifauna (Davies et al. 2007 ). This remarkable bird diversity and high endemism reflect a vast array of breeding patterns and strategies (Macedo 2008 ). Understanding these patterns is essential for developing a comprehensive life-history theory of birds (Xiao et al. 2017 ). Despite considerable research efforts, many aspects of the breeding biology of Neotropical birds remain undocumented (Xiao et al. 2017 ; Fierro-Calderón et al. 2021 ). Even during dedicated field studies, uncovering the secretive breeding lives of these birds is challenging due to unknown breeding periods, cryptic nest designs and high nest predation rates. A striking example of this knowledge gap lies withing the New World flycatchers ( see Heming et al., 2013 ). Flycatchers, the most species-rich bird family globally, comprise 381 species in South America alone (Remsen et al. 2024 ). Yet, reproductive biology has been described for only a small fraction of these species. That is unfortunate, as flycatchers exhibit diverse and intriguing life-histories (Skutch and Garner 1999 ). Their nest design alone showcase an astonishing diversity of pattern and arrangements (Ocampo et al. 2023 ). Within the Tyrannidae family, the genus Inezia comprises four recognized species distributed across South America. These diminutive Tyrannulets have been the focus of taxonomic assesments (Parkes 1973 ; Lanyon 1988 ; Fitzpatrick 2000 ; Zimmer and Whittaker 2000 ; Remsen et al. 2024 ), but their breeding biology remains largely unexplored. To date, the only documented information for the genus comes from brief descriptions of a nest and clutch of the Plain Inezia ( Inezia inornata ) in Argentina (Di Giacomo and Krapovickas 2005 ; Bodrati 2019 ). No breeding information data exist for the remaining species, including the Slender-billed Inezia ( I. tenuirostris). The Slender-billed Inezia ( I. tenuirostris ) is particularly notable as the lightest passerine bird in South America, weighing just 5 grams ( sensu Tobias et al., 2022 ). Endemic to the lowlands of northwestern Venezuela and northeastern Colombia, this species inhabits dry thorn-scrub, arid woodlands, cactus deserts, and pastures with thorny shrubs (Fitzpatrick 2000 ). Surviving is such seasonal dry-hot environments − with high temperatures, intense solar radiation, and low annual rainfall − makes I. tenuirostris a compelling subject for understanding ecological and evolutionary adaptations. In this study, we investigate the nesting biology of Inezia tenuirostris , including a description of its nests, eggs, and nestlings. We quantify nestling growth and growth rates, fit survival curves for the nesting cycle, and discuss breeding success in the context of potential adaptations to harsh environments. Notable features such as the species’ ventilated cup-shaped nests, black-skinned nestlings, and accelerated nestling growth rates are examined in relation to environmental pressures, including nest predation and extreme climatic conditions. Methods Study site We monitored a population of the Slender-billed Inezia ( Inezia tenuirostris ) on the campus of the Universidad Nacional de Colombia, Sede de La Paz (Fig. 1 , 10.390°N, -73.197°W, ~ 140 m a.s.l.; La Paz, Cesar, Colombia). The campus is located within a very dry forest life zone (Holdrige, 1967 ) near the Cesar River, between the western slope of the Sierra de Perija and the eastern slope of the Sierra Nevada de Santa Marta. The campus includes two early-successional forest patches: a northern patch (~ 23 ha) and a southern patch (~ 7 ha), see Fig. 1 . A permanent vegetation plot (0.25 ha) in the northern patch revealed a tree density (> 2.5 dhb) of 1024 trees/ha and a basal area of 10.55 m 2 ha − 1 . Dominant tree species included Vachellia tortuosa , Bulnesia arborea , Prosopis juliflora , and Cordia dentata ). The forest height distribution indicated that 79.2% of the threes were under 4 m tall, 18.4% were between 4–8 m, and 2.4% were between 8–12 m. Nests monitoring We searched for nests over ten months (January−October 2024) and located 43 nests between April 30 April and June 20, 2024. Nest were found by following adult birds or actively searching potential nesting sites across the study area. Nest were monitored daily or every other day, depending on their stage: during nest-building we monitored daily until clutch completion; after clutch completion, we monitored every other day until hatching approached, at which point monitoring resumed daily; with eggs we checked daily until hatching day; with nestlings, we monitored on hatching day (day 0), the following day (day 1), and every other day until fledging. Nest description and design We described nests using the standardized method by Hansell ( 2000 ), measuring two external nest diameters (longest and shortest), nest depth, nest width, and the diameter of the supporting branch. Nest height was measured with a 5-meter tape. All measurements, except height, were taken using a dial caliper (± 0.01 mm) within the first three days of incubation. We collected and weighed five predated (undamaged) nests during early incubation using a digital scale (± 0.01 g). We described nest composition and attachment via visual inspection. Measurements are presented as the mean ± standard deviation (SD) and sample size ( n ). Data analyses were conducted in R (R Core Team 2024 ), and all datasets and R scripts are provided as supplementary material to ensure transparency and reproducibility (see Parker et al., 2016 ). Eggs description Egg morphological data were recorded within three days of clutch completion. Egg length and width were measured with a dial caliper (± 0.01 mm), and weight was determined with a digital scale (± 0.01 g). Egg volume was calculated using Hoyt's (1979) formula Egg [volume] = 0.51 × length × width 2 . Nestlings ontogeny and growth curves We photographed nestlings at different ages and used key visual indicators to describe their ontogeny following Jongsomjit et al. ( 2007 ). To analyze growth ( n nestilngs = 18, n measurements = 82 ), we fitted a logistic function: W(t) = A / {1 + e [−K(t−ti)] } , where W(t) represents body mass at time t , A is the asymptotic body mass, t i is the inflection point, and K is the growth rate constant (Ricklefs 1967 ; Remeŝ 2007 ; Sofaer et al. 2013 ). We fitted the logistic function using the nmle package (Pinheiro and Bates 2023 ) implemented in R (R Core Team 2024 ). Growth rate ( g/day ) was derived from the logistic function’s first derivate: dw/dt = Ake [−K(t−ti)] /(e [−K(t−ti)] + 1) 2 . Nesting cycle and survival analysis The incubation period was defined as the number of days from clutch completion to hatching, and the nestling period as the days from hatching to fledging. We recorded laying and hatching patterns, and conducted a survival analysis using the Kaplan-Meier estimator (Kaplan and Meier 1958 ; Clark et al. 2003 ). We fitted survival curves for the nesting cycle ( n nests = 32 ) using the survival package implemented in R (Therneau 2020 ). To minimize bias in our approach, we assumed three conditions. First, for nests with unknown failure times, failure was assumed to occur midway between the last two visits (Nur et al. 2004 ). Second, for eight nests predated during incubation with unknown laying dates, failure time was estimated using the population's average incubation time. Third, for six nests producing nestlings with unknown laying dates, incubation duration was assigned as the average for the population. Lastly, we calculated daily nest mortality as D pr = -( ln S)/ T , where S is proportion of successful nests ( 1 - proportion of nest depredated ), and T is the nest cycle duration (Ricklefs 1969 ; Remeŝ 2007 ). We assumed nest predation when eggs or nestlings (prior fledgling age) disappeared (Martin et al. 2017 , Unzeta et al. 2020 ). Results Nests location and design We located 43 nests of Inezia tenuirostris (Fig. 1 ), of which 34 were active ( i.e . with at least one egg laid). All nests were positioned on Vachellia tortuosa , a thorny leguminous shrub common in dry habitats of northern Colombia. The birds predominantly placed their nests on the outer edges of V. tortuosa in relatively open patches dominated by this species. Despite the presence of areas with higher tree diversity and with taller canopies in the study site, but I. tenuirostris exclusively selected V. tortuosa for nesting (Fig. 1 ). The nests were remarkably small, transparent-ventilated, thin-walled, and cup-shaped (Fig. 2 ). Table 1 summarizes the weight and dimensions of the nests. Birds attached the nest to multiple small branches of V. tortuosa (Table 1 ). The nests consisted of two distinct functional layers: a structural layer and an attachment layer, with no decorative or lining layers. The structural layer comprised fine woody stems from V. tortuosa , ranging from 0.1 to 0.6 mm in diameter and 30 to 60 mm in length. These stems, often pubescent, were interwoven with arthropod silk, particularly concentrated along the rim for added structural integrity (Fig. 2 ). Also, many of these stems retained immature V. tortuosa flower globes, 2.0 to 3.0 mm in diameter. Table 1 Nest measurements of the Slender-billed Inezia ( Inezia tenuirostris ) at Universidad Nacional de Colombia, La Paz, Cesar, Colombia. Variable n Mean Standard deviation Height (m) 23 2.30 0.86 Nest weight (g) 5 0.79 0.19 Nest depth (mm) 19 27.26 4.31 Nest longest diameter (mm) 19 44.26 6.10 Nest shortest diameter (mm) 19 38.37 4.90 Nest width (mm) 10 2.55 1.34 Support diameter (mm) 15 8.42 3.60 Eggs description, clutch size, laying pattern, and incubation The eggs were pure white, lacking any marks or spots (Fig. 2 ). On average, egg length measured 13.36 mm ( SD ± 0.94 mm, n = 21), egg width was 10.52 mm ( SD ± 0.603 mm, n = 21), egg weight was 0.80 g ( SD ± 0.12 g, n = 23), and egg volume was 0.76 mm 3 ( SD ± 0.12 mm 3 , n = 21). Clutches consistently contained two eggs. Birds laid eggs either on consecutive days (24-hour interval n = 4) or on alternate days (48-hour interval n = 7 and 72-hour interval n = 1). Incubation lasted an average of 12.50 days ( SD ± 0.53 days, n = 8). Via video recordings, we captured a unique event where both parents alternated incubation duties. Nestlings description, hatching pattern and growth curves Newly hatched nestlings were altricial, naked, with blackish skin, and their eyes remained closed (Fig. 3 ). Sparse whitish down appeared on their dorsal region. The gape and flanges were yellowish, without visible mouth markings. At hatching, nestlings weighed 0.74 g ( SD ± 0.17 g, n = 18 ). By day 5, their eyes began to open, primary pins and coverts emerged, and feather tracks became visible (Fig. 3 ), with nestlings averaging 2.80 g ( SD ± 0.60 g, n = 13 ). At day 9, eyes were fully open, feather tracts continued to unsheathe, and contour feathers and wing bars appeared (Fig. 3 ). At this stage, nestlings weighed 4.17 g ( SD ± 0.33 g, n = 8 ). By day 11, nestlings were ready to fledge, with wings nearly fully developed and plumage resembling that of adults (Fig. 3 ). Their average weight reached 4.36 g ( SD ± 0.49 g, n = 5 ). Hatching occurred either synchronously (both eggs hatching the same day; n = 3) or asynchronously (one egg hatching per day; n = 5 ). The nestling period lasted 11.55 days ( SD ± 0.88 days, n = 9 ). The logistic growth model for nestling weight was W(t) = 4.577 / {1 + e [−0.424(t−3.733)] } ( n nestilngs = 18, n measurements = 82, AIC = 48.37, SE residuals = 0.32 ). Nestlings reached an asymptotic mass of 4.58 g, with maximum growth rate (0.49 g/day ) occurring at 3.73 days (Fig. 4 ). Growth slowed thereafter, reaching a minimum of 0.08 g/day by day 11. Nesting cycle and survival analysis The entire nesting cycle spanned approximately 26 days: ~2 days for nest building, 12.50 days for incubation, and 11.55 days for the nestling period. Nest construction varied between one and three days based on observations. Survival analysis ( n = 32 nests ) revealed significant nest losses during the incubation period, followed by a steadier decline during the nestling period (Fig. 5 , Table S1 ). Nest survival fell to 0.53 ( 95% CI = 0.38–0.75 ) by the end of incubation and dropped further to 0.30 ( 95% CI = 0.17–0.52 ) by the end of the nestling period (Fig. 5 ). Overall, 70% of nests failed (Fig. 5 ). Daily predation rate ( D pr ) for the entire nesting cycle was 0.043 (4.33%). These findings align with the observed outcomes for eggs, nestlings, and nests summarized in Table 2 . Table 2 Outcomes of the eggs, nestlings, and nests of the Slender-billed Inezia ( Inezia tenuirostris ) at Universidad Nacional de Colombia, La Paz, Cesar, Colombia Variable Number Percentage Total number of eggs 68 100.00 Eggs predated 30 44.12 Hatched 22 32.36 Hatching failure 8 11.76 Egg losses 6 8.82 Eggs deserted 2 2.94 Total number of nestlings 22 100.00 Nestlings predated 11 50.00 Nestlings fledged 11 50.00 Nest used 34 100.00 Nests predated (with eggs) (with nestlings) (with eggs and nestlings) 22 (15) (5) (2) 64.71 (68.18) (22.72) (9.10) Nest successful 9 26.47 Nest failed (both eggs did not hatch) 2 5.88 Nest deserted 1 2.94 Discussion In this study, we described noteworthy aspects of the reproductive biology and nesting survival of the Slender-Billed Inezia (Inezia tenuirostris), the smallest passerine bird in South America. We found that I. tenuirostris builds exceptionally small cup-shaped nests, incubates a clutch of two immaculate white eggs, and typically rears one black-skinned nestling. The complete nesting cycle lasted approximately 26 days, consisting of ~ 2 days of nest building, 12.5 days of incubation, and 11.55 days of rearing. Our growth model for nestlings revealed a rapid postnatal growth rate. Notably, nest predation during incubation significantly impacted the breeding success of I. tenuirostris . A distinctive aspect of the life history of I. tenuirostris is its peculiar, tiny cup-shaped nest. While the small size of the nest aligns with the bird’s diminutive stature, the design is atypical. As described in the results and illustrated in Fig. 6 (also see Fig. 2 ), the nests appear unfinished, translucent, and ventilated. We propose that this design and the choice of materials may help mitigate harsh climatic conditions by maintaining appropriate humidity and temperature levels for incubation and rearing (Heenan et al. 2015 ). The study site, a very dry forest with persistently high temperatures and bimodal rainfall, experienced a rainfall peak during the observed breeding season. We suggest that the nest design serves dual purposes: (1) preventing water absorption and facilitating quick drying after rainfall, and (2) reducing heat retention, which could otherwise adversely affect eggs and nestlings (Grant 1982 ; Heenan et al. 2015 ). Additionally, the nest design may provide camouflage against predators. Another striking finding is the marked black skin of the nestlings. This trait is rare among birds and has been hypothesized to function as a photoprotective barrier against UV radiation, a thermoregulator, or an antimicrobial defense (Nicolaï et al. 2020 ). Our study area, in the lowlands of northern Colombia, experiences high UV radiation levels (Beckmann et al. 2014 ). We propose that the black skin of I. tenuirostris nestlings supports the UV photoprotective hypothesis, consistent with Nicolaï et al. ( 2020 ). Given the altricial nature of these nestlings and their prolonged exposure to direct UV radiation, this adaptation seems plausible. Moreover, the black skin aligns with Gloger’s rule, which suggests that darker pigmentation is more common near the equator (Delhey 2019 ). Future studies on the other three species of Inezia, which inhabit regions from northern to southern South America, could provide further insights. We have also observed low nesting survival, predominantly due to nest predation (Martin et al. 2017 ). The highest predation losses occurred during the incubation period, primarily targeting eggs. We documented two predation events: one by a solitary Tropical Mockingbird ( Mimus gilvus ) and another by a flock of Groove-billed Anis ( Crotophaga sulcirostris ). The latter species frequently foraged in Vachellia trees, suggesting it may be a primary predator of I. tenuirostris eggs. Although we did not directly observe snake predation, it remains a potential threat. Additionally, we noted some egg losses during incubation unrelated to predation, possibly linked to heavy rainfall events. In these cases, females continued incubating the remaining egg, indicating a trade-off between the ventilated nest design and its ability to securely support eggs under adverse conditions. The high predation rate observed for this diminutive bird is consistent with findings that smaller species experience higher daily nest predation rates (Unzeta et al. 2020 ). The accelerated growth rate of nestlings could be an evolutionary response to persistent predation risk (Remeŝ 2007 ). Parents may adopt a dual strategy of (1) high feeding rates and (2) energy allocation across multiple breeding attempts rather than relying on a single attempt with fewer feeding visits (Skutch. 1949; Martin 1995 ; Martin 2014 ). Our observations support this hypothesis, as females promptly initiated new breeding attempts after predation events, and both sexes actively fed the young. Further studies are necessary to confirm these behaviors. In conclusion, we have provided the first detailed account of the life history of one of the world’s smallest passerine birds through a brief but intensive field study. Our sample size of 34 active nests is notably robust compared to most studies on Neotropical passerines, which typically report fewer nests. This success reflects our targeted approach to locating I. tenuirostris nests by focusing on specific forest locations, tree heights, and parental territorial behaviors. While further data are required to fully understand the species’ life history, our study lays the groundwork for future ecological and evolutionary research on this remarkable bird Declarations Ethical approval This research project and its protocols were approved by the Universidad Nacional de Colombia Sede de La Paz (Hermes-56887). Funding This research was funded by Universidad Nacional de Colombia. Author Contribution C.E.L Wrote the main text and conducted the analysisC.E.L., J.D.R, and A.R.G conducted fieldwork and discussed the goals.All the authors read and approved the final version of this manuscript. Acknowledgments We thank Elquin Toro Arias for providing us help in the field. This project was approved and sponsored by the Universidad Nacional de Colombia (Hermes UNAL 56887-2010100). Conflict of interest The authors have no conflict of interest to declare. 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Smithson Contrib Zool 9:1–48 Skutch AF, DO TROPICAL BIRDS REAR AS MANY YOUNG AS THEY CAN NOURISH ? (1949) Ibis 91(3):430–455. https://doi.org/10.1111/j.1474-919X.1949.tb02293.x Skutch AF, Garner D (1999) Life of the Flycatcher. Univ of Oklahoma Sofaer HR, Chapman PL, Sillett TS, Ghalambor CK (2013) Advantages of nonlinear mixed models for fitting avian growth curves. J Avian Biol 44(5):469–478. https://doi.org/10.1111/j.1600-048X.2013.05719.x Therneau TM (2020) A Package for Survival Analysis in R Tobias JA, Sheard C, Pigot AL, Devenish AJM et al (2022) AVONET: morphological, ecological and geographical data for all birds. Ecol Lett 25(3):581–597. https://doi.org/10.1111/ele.13898 Unzeta M, Martin TE, Sol D (2020) Daily Nest Predation Rates Decrease with Body Size in Passerine Birds. Am Nat 196(6):743–754. https://doi.org/10.1086/711413 Xiao H, Hu Y, Lang Z, Fang B, Guo W, Zhang Q, Pan X, Lu X (2017) How much do we know about the breeding biology of bird species in the world? J Avian Biol 48(4):513–518. https://doi.org/10.1111/jav.00934 Zimmer KJ, Whittaker A (2000) Species Limits in Pale-Tipped Tyrannulets (Inezia: Tyrannidae). Wilson Bull 112(1):51–66 Additional Declarations No competing interests reported. Supplementary Files Ineziachickdata.csv Ineziaeggdata.csv Inezianestdata.csv Ineziasurvival.csv Ineziaanalysis2025.r Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5792104","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":400321634,"identity":"e6b55ad9-992c-4f19-855d-2e81cd84c8a9","order_by":0,"name":"Carlos Esteban Lara","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYFAC5gYQKQfEjAeAPGK0MIK1GIMI0rQkNhCthb+9sfFzRc3h9A23mx8cYKiwTmxgP3wArxaJMwebJc8cO5y74c4xgwMMZ9ITG3jSEvBqMZBIbJBsYEvL3XAjweAAY9vhxAYJHgP8WuQfNv9s+JeWbnAj/cMBxn/EaJFgbJNsbLNJMLiRA7SlgQgtEmcS2ywb+2wMZ97IKTiQcCzduI2QX/jbDx++2fBNQp7vRvrGBx9qrGX7CYUYKgAZz0aC+lEwCkbBKBgFOAAAvMJLcXvWEssAAAAASUVORK5CYII=","orcid":"","institution":"Universidad Nacional de Colombia – Sede de La Paz – Dirección Académica","correspondingAuthor":true,"prefix":"","firstName":"Carlos","middleName":"Esteban","lastName":"Lara","suffix":""},{"id":400321635,"identity":"fa14c137-cdcd-4515-9947-cb7d61233254","order_by":1,"name":"Jesus David Rambaut","email":"","orcid":"","institution":"Universidad Nacional de Colombia – Sede de La Paz – Dirección Académica","correspondingAuthor":false,"prefix":"","firstName":"Jesus","middleName":"David","lastName":"Rambaut","suffix":""},{"id":400321636,"identity":"bcfe6628-1e30-4331-8f90-b66aefd3accc","order_by":2,"name":"Ángel Ramiro Gámez","email":"","orcid":"","institution":"Universidad Nacional de Colombia – Sede de La Paz – Dirección Académica","correspondingAuthor":false,"prefix":"","firstName":"Ángel","middleName":"Ramiro","lastName":"Gámez","suffix":""}],"badges":[],"createdAt":"2025-01-08 23:53:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5792104/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5792104/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":73897558,"identity":"5e07a878-88ec-4497-a2a1-afec54839c85","added_by":"auto","created_at":"2025-01-15 16:50:46","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":173608,"visible":true,"origin":"","legend":"\u003cp\u003eThe campus of Universidad Nacional de Colombia, Sede La Paz (La Paz, Cesar, Colombia), showing two forest patches in an early successional stage. The northern patch covers ~23 hectares (38 nests), and the southern patch covers ~7 hectares (5 nests). The 43 nests of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e) are represented by colored dots: ivory-colored dots indicate used nests, and yellow-colored dots indicate unused nests.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/1315504cd93f5e5e058fe638.jpg"},{"id":73897573,"identity":"b574bbd5-143f-48c3-9809-26fb745a4875","added_by":"auto","created_at":"2025-01-15 16:50:47","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1501913,"visible":true,"origin":"","legend":"\u003cp\u003eNests and eggs of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e) from different angles. The nests were composed of fine woody stems (some with tiny round globe flowers) from \u003cem\u003eVachellia tortuosa\u003c/em\u003e. The photos depict the transparent structure of the nest and the abundant silk on the rims of some nests. The photos also show the tiny, immaculate white eggs. See the text for additional information. Photos by CEL.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/2c67c2cfdecde2be1e880082.png"},{"id":73897546,"identity":"fed448ae-3af5-4cdb-996e-c679ba874927","added_by":"auto","created_at":"2025-01-15 16:50:45","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1210371,"visible":true,"origin":"","legend":"\u003cp\u003eNestlings of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e) at different ages. The top photos show nestlings on the day of hatching, the middle photos show nestlings at five days of age, and the bottom photos (left) show a nestling at nine days of age, with the bottom right photo showing a nestling at 11 days of age. Photos by CEL.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/33854c995ce3e11f6f3cd40e.png"},{"id":73898555,"identity":"3fc5eff2-8dbb-407b-aa4d-2f43a6a75b77","added_by":"auto","created_at":"2025-01-15 16:58:45","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":64614,"visible":true,"origin":"","legend":"\u003cp\u003eThe accumulated growth curve (top) and growth rate curve (bottom) for nestlings of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e). Data points were jittered horizontally by 20% to avoid overlap.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/5a5369d7eb5bac38c6e3ae3e.jpg"},{"id":73897538,"identity":"761ecc1d-ef23-483d-8faa-e6448ae0f2d1","added_by":"auto","created_at":"2025-01-15 16:50:45","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":35420,"visible":true,"origin":"","legend":"\u003cp\u003eSurvival curves, with 95% confidence intervals, for the overall nesting cycle of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e). The incubation period (green) and the nestling period (blue) are differentiated by colored watermarks.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/65f199eeb8ff3d1351b24f7a.jpg"},{"id":73897541,"identity":"91bb5063-4519-4fe0-801c-bda23a566e7b","added_by":"auto","created_at":"2025-01-15 16:50:45","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":611200,"visible":true,"origin":"","legend":"\u003cp\u003eLateral view of a Slender-billed Inezia (Inezia tenuirostris) nest. The photo depicts a completed nest with eggs being incubated. From this lateral perspective, the nest appears to be “ventilated” / “transparent.”\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/8a4519a37310ba88c9581c57.jpg"},{"id":95818760,"identity":"b9d45493-e5cf-4acf-b81e-e3612766101e","added_by":"auto","created_at":"2025-11-13 10:33:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4302461,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/b9b7a471-6683-4828-91a5-d1ec2995497a.pdf"},{"id":73899167,"identity":"c19389f5-b457-4e17-8146-c0bf740337f8","added_by":"auto","created_at":"2025-01-15 17:06:45","extension":"csv","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2964,"visible":true,"origin":"","legend":"","description":"","filename":"Ineziachickdata.csv","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/79926a25f83559b85d9306f0.csv"},{"id":73897542,"identity":"850b65c7-26a8-42ea-af95-e0ea09fb4cc7","added_by":"auto","created_at":"2025-01-15 16:50:45","extension":"csv","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":798,"visible":true,"origin":"","legend":"","description":"","filename":"Ineziaeggdata.csv","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/38d41bda0aa40225bcd202f4.csv"},{"id":73897537,"identity":"ca5a46c3-cb9a-4a0d-a13c-e85fc836305f","added_by":"auto","created_at":"2025-01-15 16:50:44","extension":"csv","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3551,"visible":true,"origin":"","legend":"","description":"","filename":"Inezianestdata.csv","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/163af5ccb9e6c204f883636d.csv"},{"id":73897556,"identity":"64930c71-0caa-4172-b8da-38c8b51caa7f","added_by":"auto","created_at":"2025-01-15 16:50:46","extension":"csv","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":15731025,"visible":true,"origin":"","legend":"","description":"","filename":"Ineziasurvival.csv","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/eb1b59567454a5ae5a5b847d.csv"},{"id":73898552,"identity":"fec1d4fa-b498-41d4-9c96-fd026c5bb79a","added_by":"auto","created_at":"2025-01-15 16:58:45","extension":"r","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":8087,"visible":true,"origin":"","legend":"","description":"","filename":"Ineziaanalysis2025.r","url":"https://assets-eu.researchsquare.com/files/rs-5792104/v1/3e1e7426d5b97332364f35a8.r"}],"financialInterests":"No competing interests reported.","formattedTitle":"Nesting biology, growth and survival of the Slender-Billed Inezia: Insights into the life history of the South America’s smallest passerine","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe neotropics are renowned for their rich and unique avifauna (Davies et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). This remarkable bird diversity and high endemism reflect a vast array of breeding patterns and strategies (Macedo \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Understanding these patterns is essential for developing a comprehensive life-history theory of birds (Xiao et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Despite considerable research efforts, many aspects of the breeding biology of Neotropical birds remain undocumented (Xiao et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Fierro-Calder\u0026oacute;n et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Even during dedicated field studies, uncovering the secretive breeding lives of these birds is challenging due to unknown breeding periods, cryptic nest designs and high nest predation rates.\u003c/p\u003e \u003cp\u003eA striking example of this knowledge gap lies withing the New World flycatchers (\u003cem\u003esee\u003c/em\u003e Heming et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Flycatchers, the most species-rich bird family globally, comprise 381 species in South America alone (Remsen et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Yet, reproductive biology has been described for only a small fraction of these species. That is unfortunate, as flycatchers exhibit diverse and intriguing life-histories (Skutch and Garner \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). Their nest design alone showcase an astonishing diversity of pattern and arrangements (Ocampo et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWithin the Tyrannidae family, the genus Inezia comprises four recognized species distributed across South America. These diminutive Tyrannulets have been the focus of taxonomic assesments (Parkes \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Lanyon \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Fitzpatrick \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Zimmer and Whittaker \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Remsen et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), but their breeding biology remains largely unexplored. To date, the only documented information for the genus comes from brief descriptions of a nest and clutch of the Plain Inezia (\u003cem\u003eInezia inornata\u003c/em\u003e) in Argentina (Di Giacomo and Krapovickas \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Bodrati \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). No breeding information data exist for the remaining species, including the Slender-billed Inezia (\u003cem\u003eI. tenuirostris).\u003c/em\u003e\u003c/p\u003e \u003cp\u003eThe Slender-billed Inezia (\u003cem\u003eI. tenuirostris\u003c/em\u003e) is particularly notable as the lightest passerine bird in South America, weighing just 5 grams (\u003cem\u003esensu\u003c/em\u003e Tobias et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Endemic to the lowlands of northwestern Venezuela and northeastern Colombia, this species inhabits dry thorn-scrub, arid woodlands, cactus deserts, and pastures with thorny shrubs (Fitzpatrick \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Surviving is such seasonal dry-hot environments \u0026minus; with high temperatures, intense solar radiation, and low annual rainfall \u0026minus; makes \u003cem\u003eI. tenuirostris\u003c/em\u003e a compelling subject for understanding ecological and evolutionary adaptations.\u003c/p\u003e \u003cp\u003eIn this study, we investigate the nesting biology of \u003cem\u003eInezia tenuirostris\u003c/em\u003e, including a description of its nests, eggs, and nestlings. We quantify nestling growth and growth rates, fit survival curves for the nesting cycle, and discuss breeding success in the context of potential adaptations to harsh environments. Notable features such as the species\u0026rsquo; ventilated cup-shaped nests, black-skinned nestlings, and accelerated nestling growth rates are examined in relation to environmental pressures, including nest predation and extreme climatic conditions.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy site\u003c/h2\u003e \u003cp\u003eWe monitored a population of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e) on the campus of the Universidad Nacional de Colombia, Sede de La Paz (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, 10.390\u0026deg;N, -73.197\u0026deg;W, ~\u0026thinsp;140 m a.s.l.; La Paz, Cesar, Colombia). The campus is located within a very dry forest life zone (Holdrige, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1967\u003c/span\u003e) near the Cesar River, between the western slope of the Sierra de Perija and the eastern slope of the Sierra Nevada de Santa Marta. The campus includes two early-successional forest patches: a northern patch (~\u0026thinsp;23 ha) and a southern patch (~\u0026thinsp;7 ha), see Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A permanent vegetation plot (0.25 ha) in the northern patch revealed a tree density (\u0026gt;\u0026thinsp;2.5 dhb) of 1024 trees/ha and a basal area of 10.55 m\u003csup\u003e2\u003c/sup\u003e ha\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Dominant tree species included \u003cem\u003eVachellia tortuosa\u003c/em\u003e, \u003cem\u003eBulnesia arborea\u003c/em\u003e, \u003cem\u003eProsopis juliflora\u003c/em\u003e, and \u003cem\u003eCordia dentata\u003c/em\u003e). The forest height distribution indicated that 79.2% of the threes were under 4 m tall, 18.4% were between 4\u0026ndash;8 m, and 2.4% were between 8\u0026ndash;12 m.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eNests monitoring\u003c/h3\u003e\n\u003cp\u003eWe searched for nests over ten months (January\u0026minus;October 2024) and located 43 nests between April 30 April and June 20, 2024. Nest were found by following adult birds or actively searching potential nesting sites across the study area. Nest were monitored daily or every other day, depending on their stage: during nest-building we monitored daily until clutch completion; after clutch completion, we monitored every other day until hatching approached, at which point monitoring resumed daily; with eggs we checked daily until hatching day; with nestlings, we monitored on hatching day (day 0), the following day (day 1), and every other day until fledging.\u003c/p\u003e\n\u003ch3\u003eNest description and design\u003c/h3\u003e\n\u003cp\u003eWe described nests using the standardized method by Hansell (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), measuring two external nest diameters (longest and shortest), nest depth, nest width, and the diameter of the supporting branch. Nest height was measured with a 5-meter tape. All measurements, except height, were taken using a dial caliper (\u0026plusmn;\u0026thinsp;0.01 mm) within the first three days of incubation. We collected and weighed five predated (undamaged) nests during early incubation using a digital scale (\u0026plusmn;\u0026thinsp;0.01 g). We described nest composition and attachment via visual inspection. Measurements are presented as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) and sample size (\u003cem\u003en\u003c/em\u003e). Data analyses were conducted in R (R Core Team \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), and all datasets and R scripts are provided as supplementary material to ensure transparency and reproducibility (see Parker et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eEggs description\u003c/h3\u003e\n\u003cp\u003eEgg morphological data were recorded within three days of clutch completion. Egg length and width were measured with a dial caliper (\u0026plusmn;\u0026thinsp;0.01 mm), and weight was determined with a digital scale (\u0026plusmn;\u0026thinsp;0.01 g). Egg volume was calculated using Hoyt's (1979) formula \u003cem\u003eEgg\u003c/em\u003e\u003csub\u003e\u003cem\u003e[volume]\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;\u003cem\u003e=\u0026thinsp;0.51 \u0026times; length \u0026times; width\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eNestlings ontogeny and growth curves\u003c/h3\u003e\n\u003cp\u003eWe photographed nestlings at different ages and used key visual indicators to describe their ontogeny following Jongsomjit et al. (\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). To analyze growth (\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003enestilngs\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e= 18, n\u003c/em\u003e\u003csub\u003e\u003cem\u003emeasurements\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e= 82\u003c/em\u003e), we fitted a logistic function: \u003cem\u003eW(t)\u0026thinsp;=\u0026thinsp;A / {1\u0026thinsp;+\u0026thinsp;e\u003c/em\u003e\u003csup\u003e\u003cem\u003e[\u0026minus;K(t\u0026minus;ti)]\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e}\u003c/em\u003e, where \u003cem\u003eW(t)\u003c/em\u003e represents body mass at time \u003cem\u003et\u003c/em\u003e, \u003cem\u003eA\u003c/em\u003e is the asymptotic body mass, \u003cem\u003et\u003c/em\u003e\u003csub\u003e\u003cem\u003ei\u003c/em\u003e\u003c/sub\u003e is the inflection point, and \u003cem\u003eK\u003c/em\u003e is the growth rate constant (Ricklefs \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1967\u003c/span\u003e; Remeŝ \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Sofaer et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). We fitted the logistic function using the \u003cem\u003enmle\u003c/em\u003e package (Pinheiro and Bates \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) implemented in R (R Core Team \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Growth rate (\u003cem\u003eg/day\u003c/em\u003e) was derived from the logistic function\u0026rsquo;s first derivate: \u003cem\u003edw/dt\u0026thinsp;=\u0026thinsp;Ake\u003c/em\u003e\u003csup\u003e\u003cem\u003e[\u0026minus;K(t\u0026minus;ti)]\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e/(e\u003c/em\u003e\u003csup\u003e\u003cem\u003e[\u0026minus;K(t\u0026minus;ti)]\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;\u003cem\u003e+\u0026thinsp;1)\u003c/em\u003e\u003csup\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eNesting cycle and survival analysis\u003c/h2\u003e \u003cp\u003eThe incubation period was defined as the number of days from clutch completion to hatching, and the nestling period as the days from hatching to fledging. We recorded laying and hatching patterns, and conducted a survival analysis using the Kaplan-Meier estimator (Kaplan and Meier \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1958\u003c/span\u003e; Clark et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). We fitted survival curves for the nesting cycle (\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003enests\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e= 32\u003c/em\u003e) using the \u003cem\u003esurvival\u003c/em\u003e package implemented in R (Therneau \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). To minimize bias in our approach, we assumed three conditions. First, for nests with unknown failure times, failure was assumed to occur midway between the last two visits (Nur et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Second, for eight nests predated during incubation with unknown laying dates, failure time was estimated using the population's average incubation time. Third, for six nests producing nestlings with unknown laying dates, incubation duration was assigned as the average for the population. Lastly, we calculated daily nest mortality as \u003cem\u003eD\u003c/em\u003e\u003csub\u003e\u003cem\u003epr\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e= -( ln S)/ T\u003c/em\u003e, where \u003cem\u003eS\u003c/em\u003e is proportion of successful nests (\u003cem\u003e1 - proportion of nest depredated\u003c/em\u003e), and \u003cem\u003eT\u003c/em\u003e is the nest cycle duration (Ricklefs \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1969\u003c/span\u003e; Remeŝ \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). We assumed nest predation when eggs or nestlings (prior fledgling age) disappeared (Martin et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, Unzeta et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eNests location and design\u003c/h2\u003e \u003cp\u003eWe located 43 nests of \u003cem\u003eInezia tenuirostris\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), of which 34 were active (\u003cem\u003ei.e\u003c/em\u003e. with at least one egg laid). All nests were positioned on \u003cem\u003eVachellia tortuosa\u003c/em\u003e, a thorny leguminous shrub common in dry habitats of northern Colombia. The birds predominantly placed their nests on the outer edges of \u003cem\u003eV. tortuosa\u003c/em\u003e in relatively open patches dominated by this species. Despite the presence of areas with higher tree diversity and with taller canopies in the study site, but \u003cem\u003eI. tenuirostris\u003c/em\u003e exclusively selected \u003cem\u003eV. tortuosa\u003c/em\u003e for nesting (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe nests were remarkably small, transparent-ventilated, thin-walled, and cup-shaped (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e summarizes the weight and dimensions of the nests. Birds attached the nest to multiple small branches of \u003cem\u003eV. tortuosa\u003c/em\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The nests consisted of two distinct functional layers: a structural layer and an attachment layer, with no decorative or lining layers. The structural layer comprised fine woody stems from \u003cem\u003eV. tortuosa\u003c/em\u003e, ranging from 0.1 to 0.6 mm in diameter and 30 to 60 mm in length. These stems, often pubescent, were interwoven with arthropod silk, particularly concentrated along the rim for added structural integrity (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Also, many of these stems retained immature \u003cem\u003eV. tortuosa\u003c/em\u003e flower globes, 2.0 to 3.0 mm in diameter.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eNest measurements of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e) at Universidad Nacional de Colombia, La Paz, Cesar, Colombia.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003en\u003c/em\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMean\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eStandard deviation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeight (m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest weight (g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest depth (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e27.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.31\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest longest diameter (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest shortest diameter (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e38.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e4.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest width (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSupport diameter (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eEggs description, clutch size, laying pattern, and incubation\u003c/h2\u003e \u003cp\u003eThe eggs were pure white, lacking any marks or spots (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). On average, egg length measured 13.36 mm (\u003cem\u003eSD\u003c/em\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.94 mm, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;21), egg width was 10.52 mm (\u003cem\u003eSD\u003c/em\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.603 mm, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;21), egg weight was 0.80 g (\u003cem\u003eSD\u003c/em\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12 g, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;23), and egg volume was 0.76 mm\u003csup\u003e3\u003c/sup\u003e (\u003cem\u003eSD\u003c/em\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12 mm\u003csup\u003e3\u003c/sup\u003e, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;21). Clutches consistently contained two eggs. Birds laid eggs either on consecutive days (24-hour interval \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;4) or on alternate days (48-hour interval \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;7 and 72-hour interval \u003cem\u003en\u0026thinsp;=\u003c/em\u003e\u0026thinsp;1). Incubation lasted an average of 12.50 days (\u003cem\u003eSD\u003c/em\u003e\u0026thinsp;\u0026plusmn;\u0026thinsp;0.53 days, \u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;8). Via video recordings, we captured a unique event where both parents alternated incubation duties.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eNestlings description, hatching pattern and growth curves\u003c/h2\u003e \u003cp\u003eNewly hatched nestlings were altricial, naked, with blackish skin, and their eyes remained closed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Sparse whitish down appeared on their dorsal region. The gape and flanges were yellowish, without visible mouth markings. At hatching, nestlings weighed 0.74 g (\u003cem\u003eSD\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17 g, n\u0026thinsp;=\u0026thinsp;18\u003c/em\u003e). By day 5, their eyes began to open, primary pins and coverts emerged, and feather tracks became visible (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), with nestlings averaging 2.80 g (\u003cem\u003eSD\u0026thinsp;\u0026plusmn;\u0026thinsp;0.60 g, n\u0026thinsp;=\u0026thinsp;13\u003c/em\u003e). At day 9, eyes were fully open, feather tracts continued to unsheathe, and contour feathers and wing bars appeared (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). At this stage, nestlings weighed 4.17 g (\u003cem\u003eSD\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33 g, n\u0026thinsp;=\u0026thinsp;8\u003c/em\u003e). By day 11, nestlings were ready to fledge, with wings nearly fully developed and plumage resembling that of adults (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Their average weight reached 4.36 g (\u003cem\u003eSD\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49 g, n\u0026thinsp;=\u0026thinsp;5\u003c/em\u003e). Hatching occurred either synchronously (both eggs hatching the same day; n\u0026thinsp;=\u0026thinsp;3) or asynchronously (one egg hatching per day; \u003cem\u003en\u0026thinsp;=\u0026thinsp;5\u003c/em\u003e). The nestling period lasted 11.55 days (\u003cem\u003eSD\u0026thinsp;\u0026plusmn;\u0026thinsp;0.88 days, n\u0026thinsp;=\u0026thinsp;9\u003c/em\u003e).\u003c/p\u003e \u003cp\u003eThe logistic growth model for nestling weight was \u003cem\u003eW(t)\u0026thinsp;=\u0026thinsp;4.577 / {1\u0026thinsp;+\u0026thinsp;e\u003c/em\u003e\u003csup\u003e\u003cem\u003e[\u0026minus;0.424(t\u0026minus;3.733)]\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e}\u003c/em\u003e (\u003cem\u003en\u003c/em\u003e\u003csub\u003e\u003cem\u003enestilngs\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e= 18, n\u003c/em\u003e\u003csub\u003e\u003cem\u003emeasurements\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e= 82, AIC\u0026thinsp;=\u0026thinsp;48.37, SE\u003c/em\u003e\u003csub\u003e\u003cem\u003eresiduals\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e= 0.32\u003c/em\u003e). Nestlings reached an asymptotic mass of 4.58 g, with maximum growth rate (0.49 \u003cem\u003eg/day\u003c/em\u003e) occurring at 3.73 days (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Growth slowed thereafter, reaching a minimum of 0.08 g/day by day 11.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eNesting cycle and survival analysis\u003c/h2\u003e \u003cp\u003eThe entire nesting cycle spanned approximately 26 days: ~2 days for nest building, 12.50 days for incubation, and 11.55 days for the nestling period. Nest construction varied between one and three days based on observations. Survival analysis (\u003cem\u003en\u0026thinsp;=\u0026thinsp;32 nests\u003c/em\u003e) revealed significant nest losses during the incubation period, followed by a steadier decline during the nestling period (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Nest survival fell to 0.53 (\u003cem\u003e95% CI\u0026thinsp;=\u0026thinsp;0.38\u0026ndash;0.75\u003c/em\u003e) by the end of incubation and dropped further to 0.30 (\u003cem\u003e95% CI\u0026thinsp;=\u0026thinsp;0.17\u0026ndash;0.52\u003c/em\u003e) by the end of the nestling period (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Overall, 70% of nests failed (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Daily predation rate (\u003cem\u003eD\u003c/em\u003e\u003csub\u003e\u003cem\u003epr\u003c/em\u003e\u003c/sub\u003e) for the entire nesting cycle was 0.043 (4.33%). These findings align with the observed outcomes for eggs, nestlings, and nests summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOutcomes of the eggs, nestlings, and nests of the Slender-billed Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e) at Universidad Nacional de Colombia, La Paz, Cesar, Colombia\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVariable\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNumber\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePercentage\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal number of eggs\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e68\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100.00\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEggs predated\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44.12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHatched\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e32.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHatching failure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e11.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEgg losses\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8.82\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEggs deserted\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTotal number of nestlings\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e22\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e100.00\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNestlings predated\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNestlings fledged\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNest used\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e34\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e100.00\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNests predated\u003c/p\u003e \u003cp\u003e(with eggs)\u003c/p\u003e \u003cp\u003e(with nestlings)\u003c/p\u003e \u003cp\u003e(with eggs and nestlings)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e22\u003c/p\u003e \u003cp\u003e(15)\u003c/p\u003e \u003cp\u003e(5)\u003c/p\u003e \u003cp\u003e(2)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e64.71\u003c/p\u003e \u003cp\u003e(68.18)\u003c/p\u003e \u003cp\u003e(22.72)\u003c/p\u003e \u003cp\u003e(9.10)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest successful\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e26.47\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest failed\u003c/p\u003e \u003cp\u003e(both eggs did not hatch)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.88\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNest deserted\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we described noteworthy aspects of the reproductive biology and nesting survival of the Slender-Billed Inezia (Inezia tenuirostris), the smallest passerine bird in South America. We found that I. tenuirostris builds exceptionally small cup-shaped nests, incubates a clutch of two immaculate white eggs, and typically rears one black-skinned nestling. The complete nesting cycle lasted approximately 26 days, consisting of ~\u0026thinsp;2 days of nest building, 12.5 days of incubation, and 11.55 days of rearing. Our growth model for nestlings revealed a rapid postnatal growth rate. Notably, nest predation during incubation significantly impacted the breeding success of \u003cem\u003eI. tenuirostris\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eA distinctive aspect of the life history of \u003cem\u003eI. tenuirostris\u003c/em\u003e is its peculiar, tiny cup-shaped nest. While the small size of the nest aligns with the bird\u0026rsquo;s diminutive stature, the design is atypical. As described in the results and illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e (also see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), the nests appear unfinished, translucent, and ventilated. We propose that this design and the choice of materials may help mitigate harsh climatic conditions by maintaining appropriate humidity and temperature levels for incubation and rearing (Heenan et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The study site, a very dry forest with persistently high temperatures and bimodal rainfall, experienced a rainfall peak during the observed breeding season. We suggest that the nest design serves dual purposes: (1) preventing water absorption and facilitating quick drying after rainfall, and (2) reducing heat retention, which could otherwise adversely affect eggs and nestlings (Grant \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Heenan et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Additionally, the nest design may provide camouflage against predators.\u003c/p\u003e \u003cp\u003eAnother striking finding is the marked black skin of the nestlings. This trait is rare among birds and has been hypothesized to function as a photoprotective barrier against UV radiation, a thermoregulator, or an antimicrobial defense (Nicola\u0026iuml; et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Our study area, in the lowlands of northern Colombia, experiences high UV radiation levels (Beckmann et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). We propose that the black skin of \u003cem\u003eI. tenuirostris\u003c/em\u003e nestlings supports the UV photoprotective hypothesis, consistent with Nicola\u0026iuml; et al. (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Given the altricial nature of these nestlings and their prolonged exposure to direct UV radiation, this adaptation seems plausible. Moreover, the black skin aligns with Gloger\u0026rsquo;s rule, which suggests that darker pigmentation is more common near the equator (Delhey \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Future studies on the other three species of Inezia, which inhabit regions from northern to southern South America, could provide further insights.\u003c/p\u003e \u003cp\u003eWe have also observed low nesting survival, predominantly due to nest predation (Martin et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The highest predation losses occurred during the incubation period, primarily targeting eggs. We documented two predation events: one by a solitary Tropical Mockingbird (\u003cem\u003eMimus gilvus\u003c/em\u003e) and another by a flock of Groove-billed Anis (\u003cem\u003eCrotophaga sulcirostris\u003c/em\u003e). The latter species frequently foraged in Vachellia trees, suggesting it may be a primary predator of I. tenuirostris eggs. Although we did not directly observe snake predation, it remains a potential threat. Additionally, we noted some egg losses during incubation unrelated to predation, possibly linked to heavy rainfall events. In these cases, females continued incubating the remaining egg, indicating a trade-off between the ventilated nest design and its ability to securely support eggs under adverse conditions.\u003c/p\u003e \u003cp\u003eThe high predation rate observed for this diminutive bird is consistent with findings that smaller species experience higher daily nest predation rates (Unzeta et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The accelerated growth rate of nestlings could be an evolutionary response to persistent predation risk (Remeŝ \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Parents may adopt a dual strategy of (1) high feeding rates and (2) energy allocation across multiple breeding attempts rather than relying on a single attempt with fewer feeding visits (Skutch. 1949; Martin \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Martin \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Our observations support this hypothesis, as females promptly initiated new breeding attempts after predation events, and both sexes actively fed the young. Further studies are necessary to confirm these behaviors.\u003c/p\u003e \u003cp\u003eIn conclusion, we have provided the first detailed account of the life history of one of the world\u0026rsquo;s smallest passerine birds through a brief but intensive field study. Our sample size of 34 active nests is notably robust compared to most studies on Neotropical passerines, which typically report fewer nests. This success reflects our targeted approach to locating \u003cem\u003eI. tenuirostris\u003c/em\u003e nests by focusing on specific forest locations, tree heights, and parental territorial behaviors. While further data are required to fully understand the species\u0026rsquo; life history, our study lays the groundwork for future ecological and evolutionary research on this remarkable bird\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eEthical approval\u003c/h2\u003e \u003cp\u003eThis research project and its protocols were approved by the Universidad Nacional de Colombia Sede de La Paz (Hermes-56887).\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research was funded by Universidad Nacional de Colombia.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eC.E.L Wrote the main text and conducted the analysisC.E.L., J.D.R, and A.R.G conducted fieldwork and discussed the goals.All the authors read and approved the final version of this manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eWe thank Elquin Toro Arias for providing us help in the field. This project was approved and sponsored by the Universidad Nacional de Colombia (Hermes UNAL 56887-2010100).\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConflict of interest\u003c/strong\u003e \u003cp\u003eThe authors have no conflict of interest to declare.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll the datasets and r scripts are provided as supplementary information files\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBeckmann M, V\u0026aacute;clav\u0026iacute;k T, Manceur AM, Šprtov\u0026aacute; L, von Wehrden H, Welk E, Cord AF (2014) glUV: a global UV-B radiation data set for macroecological studies. 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Wilson Bull 112(1):51\u0026ndash;66\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"nest design, reproductive success, neotropics, life-history, tropical dry forest, predation","lastPublishedDoi":"10.21203/rs.3.rs-5792104/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5792104/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Slender-bill Inezia (\u003cem\u003eInezia tenuirostris\u003c/em\u003e) is notable as the lightest passerine bird in South America. This species is endemic to the lowlands of northwestern Venezuela and northeastern Colombia, where it inhabits seasonal dry and hot environments. Until now, little was known about its reproductive biology. In this study, we described and evaluate key aspects of the nesting biology of \u003cem\u003eI. tenuirostris\u003c/em\u003e. To achieve this, we monitored 43 nests located in forest patches within a very dry forest in an early successional stage. The nests were tiny \u0026ldquo;ventilated\u0026rdquo; cups constructed from fine woody stems. Clutch size consisted of two immaculate white eggs, which were incubated for an average of 12.5 days. At hatching, nestlings had black skin with sparse whitish down on the dorsal area and fledged after 11.6 days. The growth rate of the nestlings \u003cem\u003eK\u003c/em\u003e was 0.42, with the maximum growth rate occurring after 3.73 days post-hatching, reaching 0.49 grams/day. Survival analysis revealed a sharp decline in nest survival during incubation (a 47% reduction) and a steady decline during chick-rearing (a 23% reduction), resulting in an overall low nesting survival rate of 30%. Our findings suggest potentially intriguing adaptations in \u003cem\u003eI. tenuirostris\u003c/em\u003e for surviving in harsh environments, including: (1) the ventilated cup-shaped nest, which likely reduces water absorption and/or mitigates overheating; (2) the black skin of nestlings, which may provide photoprotection against harmful UV radiation; and (3) the accelerated growth rate of nestlings is potentially an evolutionary response to the persistent risk of nest predation.\u003c/p\u003e","manuscriptTitle":"Nesting biology, growth and survival of the Slender-Billed Inezia: Insights into the life history of the South America’s smallest passerine","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-01-15 16:50:39","doi":"10.21203/rs.3.rs-5792104/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7f3b7675-9cd2-4d5a-9c43-056e63c82319","owner":[],"postedDate":"January 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-11-12T17:23:36+00:00","versionOfRecord":[],"versionCreatedAt":"2025-01-15 16:50:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5792104","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5792104","identity":"rs-5792104","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}