Social interactions change with season and age in Northern Bald Ibis

Verena Puehringer-Sturmayr,Didone Frigerio,Tanja Stiefel,Kurt Kotrschal,Sonia Kleindorfer

doi:10.1007/s10336-020-01824-2

Abstract

Understanding the association between an individual’s position within a social network and its sex and age across seasons can be useful information for conservation management. For example, identifying the social position of females within a group can provide insights into reproductive potential, while the position of juveniles may be related to survival and hence recruitment potential. In the present study, we used social network analysis to investigate the effects of season, sex, age and reproductive partner on social interactions in the endangered Northern Bald Ibis (Geronticus eremita). Via focal sampling we recorded the social behaviour of 39 individually marked, free-flying birds for 4 months over two seasons (autumn, winter). We observed the occurrence of affiliative and agonistic interactions and estimated proximity between colony members. We found that (1) individuals were in proximity with more colony members in winter than in autumn, and affiliative interactions occurred more often in winter, (2) older individuals occupied more central positions in the proximity network irrespective of sex, (3) males engaged more than females in agonistic interactions, whereas females received more affiliative interactions than males irrespective of age, and (4) most affiliative interactions occurred between former or potentially prospective reproductive partners. Our findings suggest that social relationships could modulate inter-individual distance and there may be sex-related differences in the investment into pair bond maintenance. Overall the findings of sex- and age-related differences in behaviour and social position contribute to understanding factors associated with breeding success and mortality risk in an endangered bird species.

Highlights

Sociality influences survival and reproductive success (Davies et al 2012) via modulating the costs and benefits associated with predation risk, access to food (Krause and Ruxton 2002), and information (Dall et al 2005)
We found no effect of season or reproductive partner, but effects of age and sex on patterns of agonistic interactions
We recorded (1) lower interindividual distance during autumn compared with winter, (2) no seasonal difference in patterns of agonistic behaviour but more agonistic interactions in males than females, (3) seasonal and sex differences in affiliative behaviour with more affiliative behaviour during winter and more affiliative behaviour received by females than males, (4) reproductive partners as preferred affiliative interaction partners, and (5) an effect of age on social and centrality position within the group, with younger birds being less central in the proximity network and receiving more agonistic interactions

Summary

Introduction

Sociality influences survival and reproductive success (Davies et al 2012) via modulating the costs and benefits associated with predation risk, access to food (Krause and Ruxton 2002), and information (Dall et al 2005). Older adult Yellow-Bellied Marmots seem to initiate more and receive fewer agonistic interactions than younger adults (Wey and Blumstein 2010) This may increase male reproductive success, because females tend to prefer competitive males (Hirsch and Maldonado 2011). Social relationships within groups can be quantified by network analysis, which is a useful tool to quantify sex and age patterns of affiliative and agonistic interactions and proximity in group living animals. Such knowledge can be applied to better understand individual variation in species of conservation concern (Jacoby et al 2011; Snijders et al 2017)

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Results

Conclusion