Experimentally assessing the role of foraging encounters on social partner choice in a kin-biased bird society

Experimentally assessing the role of foraging encounters on social partner choice in a kin-biased bird society | bioRxiv /* */ /* */ <!-- <!-- /*! * yepnope1.5.4 * (c) WTFPL, GPLv2 */ (function(a,b,c){function d(a){return"[object Function]"==o.call(a)}function e(a){return"string"==typeof a}function f(){}function g(a){return!a||"loaded"==a||"complete"==a||"uninitialized"==a}function h(){var a=p.shift();q=1,a?a.t?m(function(){("c"==a.t?B.injectCss:B.injectJs)(a.s,0,a.a,a.x,a.e,1)},0):(a(),h()):q=0}function i(a,c,d,e,f,i,j){function k(b){if(!o&&g(l.readyState)&&(u.r=o=1,!q&&h(),l.onload=l.onreadystatechange=null,b)){"img"!=a&&m(function(){t.removeChild(l)},50);for(var d in y[c])y[c].hasOwnProperty(d)&&y[c][d].onload()}}var j=j||B.errorTimeout,l=b.createElement(a),o=0,r=0,u={t:d,s:c,e:f,a:i,x:j};1===y[c]&&(r=1,y[c]=[]),"object"==a?l.data=c:(l.src=c,l.type=a),l.width=l.height="0",l.onerror=l.onload=l.onreadystatechange=function(){k.call(this,r)},p.splice(e,0,u),"img"!=a&&(r||2===y[c]?(t.insertBefore(l,s?null:n),m(k,j)):y[c].push(l))}function j(a,b,c,d,f){return q=0,b=b||"j",e(a)?i("c"==b?v:u,a,b,this.i++,c,d,f):(p.splice(this.i++,0,a),1==p.length&&h()),this}function k(){var a=B;return a.loader={load:j,i:0},a}var l=b.documentElement,m=a.setTimeout,n=b.getElementsByTagName("script")[0],o={}.toString,p=[],q=0,r="MozAppearance"in l.style,s=r&&!!b.createRange().compareNode,t=s?l:n.parentNode,l=a.opera&&"[object Opera]"==o.call(a.opera),l=!!b.attachEvent&&!l,u=r?"object":l?"script":"img",v=l?"script":u,w=Array.isArray||function(a){return"[object Array]"==o.call(a)},x=[],y={},z={timeout:function(a,b){return b.length&&(a.timeout=b[0]),a}},A,B;B=function(a){function b(a){var a=a.split("!"),b=x.length,c=a.pop(),d=a.length,c={url:c,origUrl:c,prefixes:a},e,f,g;for(f=0;f<d;f++)g=a[f].split("="),(e=z[g.shift()])&&(c=e(c,g));for(f=0;f<b;f++)c=x[f](c);return c}function g(a,e,f,g,h){var i=b(a),j=i.autoCallback;i.url.split(".").pop().split("?").shift(),i.bypass||(e&&(e=d(e)?e:e[a]||e[g]||e[a.split("/").pop().split("?")[0]]),i.instead?i.instead(a,e,f,g,h):(y[i.url]?i.noexec=!0:y[i.url]=1,f.load(i.url,i.forceCSS||!i.forceJS&&"css"==i.url.split(".").pop().split("?").shift()?"c":c,i.noexec,i.attrs,i.timeout),(d(e)||d(j))&&f.load(function(){k(),e&&e(i.origUrl,h,g),j&&j(i.origUrl,h,g),y[i.url]=2})))}function h(a,b){function c(a,c){if(a){if(e(a))c||(j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}),g(a,j,b,0,h);else if(Object(a)===a)for(n in m=function(){var b=0,c;for(c in a)a.hasOwnProperty(c)&&b++;return b}(),a)a.hasOwnProperty(n)&&(!c&&!--m&&(d(j)?j=function(){var a=[].slice.call(arguments);k.apply(this,a),l()}:j[n]=function(a){return function(){var b=[].slice.call(arguments);a&&a.apply(this,b),l()}}(k[n])),g(a[n],j,b,n,h))}else!c&&l()}var h=!!a.test,i=a.load||a.both,j=a.callback||f,k=j,l=a.complete||f,m,n;c(h?a.yep:a.nope,!!i),i&&c(i)}var i,j,l=this.yepnope.loader;if(e(a))g(a,0,l,0);else if(w(a))for(i=0;i (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0];var j=d.createElement(s);var dl=l!='dataLayer'?'&l='+l:'';j.src='//www.googletagmanager.com/gtm.js?id='+i+dl;j.type='text/javascript';j.async=true;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-M677548'); Skip to main content Home About Submit ALERTS / RSS Search for this keyword Advanced Search New Results Experimentally assessing the role of foraging encounters on social partner choice in a kin-biased bird society Babette Fourie , Claire Doutrelant , Yoann Depalle , Andre C. Ferreira , Rita Covas doi: https://doi.org/10.1101/2025.11.03.686260 Babette Fourie a CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto , 4485-661 Vairão, Portugal b BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO , Campus de Vairão, 4485- 661 Vairão, Portugal Find this author on Google Scholar Find this author on PubMed Search for this author on this site For correspondence: babettefourie{at}gmail.com Claire Doutrelant c CEFE, Univ Montpellier, CNRS, EPHE, IRD , Montpellier, France d FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town , Rondebosch 7701, South Africa Find this author on Google Scholar Find this author on PubMed Search for this author on this site Yoann Depalle Find this author on Google Scholar Find this author on PubMed Search for this author on this site Andre C. Ferreira a CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto , 4485-661 Vairão, Portugal b BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO , Campus de Vairão, 4485- 661 Vairão, Portugal c CEFE, Univ Montpellier, CNRS, EPHE, IRD , Montpellier, France e Department of Evolutionary Biology and Environmental Science, University of Zurich , Zurich 8057, Switzerland Find this author on Google Scholar Find this author on PubMed Search for this author on this site Rita Covas a CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, InBIO Laboratório Associado, Campus de Vairão, Universidade do Porto , 4485-661 Vairão, Portugal b BIOPOLIS Program in Genomics, Biodiversity and Land Planning, CIBIO , Campus de Vairão, 4485- 661 Vairão, Portugal d FitzPatrick Institute of African Ornithology, DST-NRF Centre of Excellence, University of Cape Town , Rondebosch 7701, South Africa Find this author on Google Scholar Find this author on PubMed Search for this author on this site Abstract Full Text Info/History Metrics Supplementary material Data/Code Preview PDF Abstract Kin-biased social environments are often characterized by prolonged parental care and limited dispersal, leading to strong preferences for kin as social partners. These high rates of social interactions among relatives in cooperative societies make it difficult to distinguish whether social partner choice is driven by kinship or by repeated encounters with individuals situated at proximity. Here, we experimentally increased the number of foraging encounters among non-kin at a custom feeder setup in the sociable weaver (Philetairus socius ), a colonial, cooperatively breeding bird with a kin-biased social structure. Individuals encouraged to forage more frequently with non-relatives subsequently developed stronger foraging associations with non-kin at separate, unrestricted feeders. These findings show that repeated opportunities for interaction can promote non-kin social bonds even within a kin-biased society, contributing to the understanding of proximate mechanisms that underly social structure. Introduction Inclusive fitness theory ( 1 ) provides a powerful explanation for the evolution of social behaviour by predicting that individuals can gain indirect fitness benefits by associating and cooperating with kin ( 2 ) in addition to any possible direct fitness benefits ( 3 ). Such indirect fitness benefits can arise if individuals actively select to associate with kin (i.e. discriminate altruism; 4) or associate and cooperate with kin as a result of spatial overlap with relatives (i.e. population viscosity leading to indiscriminate altruism: 5, 1). As individuals in kin-structured populations are typically born into and remain near kin during development, disentangling the effects of active kin preference from spatial proximity becomes challenging. Observations of kin-biased associations are often interpreted to be evidence for indirect fitness benefits ( 6 ), however this alone does not constitute evidence that any fitness benefits arise from specifically associating with kin. For example, vampire bats ( Desmodus rotundus) engage in reciprocal food sharing with hungry social partners, including both non-relatives and relatives ( 7 ) and in Assamese macaques ( Macaca assamensis) , where individuals form enduring stable relationships, or “ social bonds”, that affect fitness, they often prefer to form bonds with non-kin over kin ( 8 ). Similarly, in approximately 30% of cooperatively breeding bird species, there is a mix of related and unrelated helpers ( 9 ). These studies suggest that the proximate mechanisms of social partner choice have implications for understanding the ultimate benefits of cooperation. Experimentally investigating the proximate mechanisms underlying social bond formation, particularly in kin-biased societies, can help us to understand social partner choice, and whether helping kin or non-kin ultimately constitutes evidence for indirect fitness benefits, kin discrimination errors ( 10 ) or direct benefits ( 7 ). Such experiments can also reveal how population ( 5 ) and social ( 11 ) viscosity limit the options for social partner choice. In kin-biased societies, some previous studies relied on cross-fostering experiments to investigate the proximate causes of social bonds ( 12 ). A natural approach is to study foraging interactions of individuals during adulthood where repeated encounters can promote and maintain social bonds that might eventually lead to cooperative interactions. Sociable weavers (Philetairus socius) are an excellent study system to test whether social partner choice is shaped by repeated foraging opportunities to associate. They are colonial cooperative breeders that form kin-biased associations for breeding ( 13 - 14 ), roosting ( 15 ), and foraging ( 16 ). Most helpers at the nest are kin (13; Ferreira et al. in prep) and form social bonds with breeders, which can be detected during foraging ( 16 ). Foraging offers a key context for social bond formation, providing benefits such as improved information access and reduced predation risk. We designed a new experimental method to test whether artificially increasing foraging encounters between non-kin leads to the formation and strengthening of non-kin social associations. The study was conducted on three wild colonies of sociable weavers at a long-term study site in Benfontein Nature Reserve, South Africa ( 13 ). Using RFID technology (Radio Frequency Identification), we designed selective feeders that restricted food access among kin (i.e., preferred foraging partners) and instead encouraged less-related individuals (typically less preferred foraging partners) to feed together ( Figure 1 ; SI appendix). We created experimental groups, by combining genetic relatedness data with clustering algorithms (Louvain & hierarchical clustering, see SI appendix) to divide individuals into clusters that minimized within-group relatedness. Each cluster of less-related individuals was assigned to a single restrictive feeder within a station of three or four feeders ( Figure 1 ). After a period of habituation (May – October), we conducted a restrictive manipulation phase (November) during which individuals from each cluster could feed either alone or with other less-related members of their assigned group (SI appendix). We assessed the effect of this manipulation by constructing time-overlap social networks ( 16 ) from foraging associations recorded at spatially separate, unrestricted feeders both before (January-April 2024) and after the manipulation (December 2024; Figure 1 ). Download figure Open in new tab Figure 1. Three stages of the experiment: (A) Pre-manipulation social foraging associations were recorded at unrestricted feeders, showing natural kin-biased preferences. (B) Individuals were grouped into artificial clusters with low genetic relatedness and given access to restrictive feeders controlled by RFID technology, allowing only artificial cluster members to feed together. (C) Post-manipulation associations from unrestricted feeders showed a 39% increase in associations within artificial clusters. Each sociable weaver colony had access to one unrestricted and one restricted feeding station at separate locations. Each sociable weaver colony had access to their own restricted and unrestricted feeding stations. The experimental design encouraged gradual interactions among non-kin without disrupting long-term bonds by allowing extended habituation periods, and natural group flocking to feeders positioned close together, while manipulating which individuals could feed side by side. Results The artificial clusters had significantly lower relatedness than natural foraging groups (Welch’s t-test: t = –3.44, p < 0.05, 95% CI [–0.20, –0.04]; mean related edge proportion: artificial = 0.043, natural = 0.165). During the manipulation at the restrictive feeders, assortativity coefficients indicated that dyads within the same artificial clusters increased their foraging encounters, shifting from negative values before the manipulation (limited within-cluster mixing) to positive values during the manipulation (increased encounters; Colony 8, r = - 0.019 to 0.257; Colony 11, r = -0.127 to 0.105; Colony 71, r = -0.119 to 0.135). To test for a change in foraging associations, we fitted a linear mixed-effects model with pairwise association strength as the response variable. Fixed effects included the experimental period (pre- or post-manipulation) as an interaction with dyad type (whether individuals were in the same artificial cluster or not). Colony and dyad identity were included as random terms. After the experiment, association strengths between individuals in the same artificial cluster significantly increased at the unrestricted feeders by 39% (Experimental period * Dyad Type: Estimate = 0.0217, SE = 0.0076, p = 0.004; Figure 2 ; SI appendix). In contrast, no significant change was detected between associations of individuals in different artificial clusters (Estimate = 0.0005, SE = 0.0033, p = 0.879; Figure 2 ). Download figure Open in new tab Figure 2. Foraging association strengths before and after the experimental manipulation. Linear mixed model results compare dyads between different artificial clusters (red) and within the same artificial cluster (blue). Before the manipulation, within and between cluster associations were similar (0.056 and 0.061, respectively). After the manipulation, within-cluster associations increased to 0.079, while between-cluster associations remained stable at 0.062. Dashed lines represent the mean association strengths in each pairwise cluster comparison within colonies (e.g., dyads within cluster 1 and dyads between clusters 1–2, 1–3, etc.) across experimental periods. Discussion Our results show that foraging associations increased among less-related individuals that were encouraged to feed together during the manipulation. To our knowledge, no previous studies have experimentally tested whether non-kin foraging encounters can facilitate the development of non-kin associations within a kin-biased social system. These findings support the idea that, even in kin-biased social systems, repeated interaction opportunities can foster non-kin bonds. This raises the question of which benefits these bonds can bring to the individuals involved, and even whether they can lead to cooperative interactions among them. Our results also have important implications for interpreting what constitutes evidence for kin selection: apparently choosing to help kin over non-kin (or closer over more distant relatives) is likely to reflect spatial and social network constraints in social bond development as much as shared genes. This overlap may confound interpretations of the relative roles of direct and indirect fitness benefits of cooperation and deserves further empirical and experimental investigation. Acknowledgments We thank Franck Theron and all field workers who helped with electronics and RFID data collection, particularly Antoine Grissot, Leo Jhaveri, Irene Baquero, Cristina Jimenez, and Hippolyte Dupas. Thanks to Damien Farine for his comments on the manuscript. De Beers Consolidated Mines provided access to Benfontein Reserve. This study was funded by an ERC Consolidator grant 866489 (EU) to RC; OSU OREME and SEE-Life (CNRS, France) to CD; FCT (CEECIND/03451/2018) to RC. Funder Information Declared Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa , CEECIND/03451/2018 European Research Council (ERC) , 866489 Footnotes ↵ 1 co-last authorship Competing Interest Statement: The authors declare no competing interests. https://figshare.com/s/e782717837a627810bf1 References 1. ↵ WD Hamilton . The genetical evolution of social behaviour. II . J Theor Biol 7 ( 1 ): 17 – 52 , 1964 . doi: 10.1016/0022-5193(64)90039-6 OpenUrl CrossRef PubMed Web of Science 2. ↵ J Smith . Group selection and kin selection . Nature 201 : 1145 – 1147 , 1964 . doi: 10.1038/2011145a0 OpenUrl CrossRef Web of Science 3. ↵ T Clutton-Brock . Cooperation between non-kin in animal societies . Nature 462 ( 7269 ): 51 – 57 , 2009 . OpenUrl CrossRef PubMed Web of Science 4. M Taborsky , MA Cant , J Komdeur . The evolution of social behaviour . Cambridge University Press , 2021 . doi: 10.1017/9780511894794 OpenUrl CrossRef 5. ↵ J Mitteldorf , DS Wilson . Population viscosity and the evolution of altruism . J Theor Biol 204 ( 4 ): 481 – 496 , 2000 . doi: 10.1006/jtbi.2000.2007 OpenUrl CrossRef PubMed Web of Science 6. ↵ JL Dickinson , BJ Hatchwell . Fitness consequences of helping . In Ecology and Evolution of Cooperative Breeding in Birds , pp. 48 – 66 , 2004 . 7. ↵ GG Carter , GS Wilkinson . Food sharing in vampire bats: Reciprocal help predicts donations more than relatedness or harassment . Proc R Soc B 280 ( 1753 ): 20122573 , 2013 . doi: 10.1098/rspb.2012.2573 OpenUrl CrossRef PubMed 8. ↵ D De Moor , C Roos , J Ostner , O Schülke . Bonds of bros and brothers: Kinship and social bonding in postdispersal male macaques . Mol Ecol 29 ( 17 ): 3346 – 3360 , 2020 . doi: 10.1111/mec.15560 OpenUrl CrossRef 9. ↵ C Riehl . Evolutionary routes to non-kin cooperative breeding in birds . Proc Biol Sci 280 ( 1772 ): 20132245 , 2013 . doi: 10.1098/rspb.2013.2245 OpenUrl CrossRef PubMed 10. ↵ J Morinay , BK Woodward , AF Russell , SP Sharp , BJ Hatchwell . Ecological and demographic drivers of kin-directed cooperation in a social bird . J Anim Ecol, in press , 2025 . doi: 10.1111/1365-2656.14237 OpenUrl CrossRef 11. ↵ AM Grabowska-Zhang , CA Hinde , CJ Garroway , BC Sheldon . Wherever I may roam: Social viscosity and kin affiliation in a wild population despite natal dispersal . Behav Ecol 27 ( 4 ): 1263 – 1268 , 2016 . OpenUrl CrossRef PubMed 12. ↵ SP Sharp , A McGowan , MJ Wood , BJ Hatchwell . Learned kin recognition cues in a social bird . Nature 434 ( 7037 ): 1127 – 1130 , 2005 . OpenUrl CrossRef PubMed Web of Science 13. ↵ R Covas , A Dalecky , A Caizergues , C Doutrelant . Kin associations and direct vs. indirect fitness benefits in colonial cooperatively breeding sociable weavers Philetairus socius . Behav Ecol Sociobiol 60 ( 3 ): 323 – 331 , 2006 . doi: 10.1007/s00265-006-0168-2 OpenUrl CrossRef Web of Science 14. ↵ AC Ferreira et al. Foraging associations are related with helping interactions in a cooperatively breeding bird . bioRxiv , 2024 . doi: 10.1101/2024.10.28.620677 OpenUrl Abstract / FREE Full Text 15. ↵ M Paquet , C Doutrelant , M Loubon , F Theron , M Rat , R Covas . Communal roosting, thermoregulatory benefits and breeding group size predictability in cooperatively breeding sociable weavers . J Avian Biol 47 ( 6 ): 663 – 672 , 2016 . doi: 10.1111/jav.00916 OpenUrl CrossRef 16. ↵ AC Ferreira et al. How to make methodological decisions when inferring social networks . Ecol Evol 10 ( 17 ): 9132 – 9143 , 2020 . doi: 10.1002/ece3.6568 OpenUrl CrossRef View the discussion thread. Back to top Previous Next Posted November 04, 2025. Download PDF Supplementary Material Data/Code Email Thank you for your interest in spreading the word about bioRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. You are going to email the following Experimentally assessing the role of foraging encounters on social partner choice in a kin-biased bird society Message Subject (Your Name) has forwarded a page to you from bioRxiv Message Body (Your Name) thought you would like to see this page from the bioRxiv website. Your Personal Message CAPTCHA This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. Share Experimentally assessing the role of foraging encounters on social partner choice in a kin-biased bird society Babette Fourie , Claire Doutrelant , Yoann Depalle , Andre C. Ferreira , Rita Covas bioRxiv 2025.11.03.686260; doi: https://doi.org/10.1101/2025.11.03.686260 Share This Article: Copy Citation Tools Experimentally assessing the role of foraging encounters on social partner choice in a kin-biased bird society Babette Fourie , Claire Doutrelant , Yoann Depalle , Andre C. Ferreira , Rita Covas bioRxiv 2025.11.03.686260; doi: https://doi.org/10.1101/2025.11.03.686260 Citation Manager Formats BibTeX Bookends EasyBib EndNote (tagged) EndNote 8 (xml) Medlars Mendeley Papers RefWorks Tagged Ref Manager RIS Zotero Tweet Widget Facebook Like Google Plus One Subject Area Animal Behavior and Cognition Subject Areas All Articles Animal Behavior and Cognition (7635) Biochemistry (17697) Bioengineering (13895) Bioinformatics (41951) Biophysics (21456) Cancer Biology (18594) Cell Biology (25520) Clinical Trials (138) Developmental Biology (13381) Ecology (19903) Epidemiology (2067) Evolutionary Biology (24323) Genetics (15612) Genomics (22510) Immunology (17738) Microbiology (40401) Molecular Biology (17184) Neuroscience (88622) Paleontology (667) Pathology (2833) Pharmacology and Toxicology (4825) Physiology (7644) Plant Biology (15158) Scientific Communication and Education (2046) Synthetic Biology (4296) Systems Biology (9825) Zoology (2271)