Similarity in sex and reproductive state, but not relatedness, influence the strength of association in the social network of feral horses in the Blauwe Kamer Nature Reserve

Abstract

Relatedness is likely to affect the decisions of animals regarding their affiliations with conspecifics. Social network analysis provides tools to describe the social structure of animals. Here, we investigate the social network of a population of 27 unmanaged Konik horses in the Blauwe Kamer Nature Reserve, in the Netherlands. We test three hypotheses: (1) that related individuals will have stronger associations; (2) that individuals with low values of average relatedness to their neighbors in the network will have more links and (3) homophily, the tendency of individuals to associate with similar others, will lead to stronger associations among individuals of similar sex, reproductive state, age and rank in the social network. We videotaped 22 horses (excluding foals) and their interactions. Relatedness was calculated from the pedigree, which was based on parentage, determined by DNA analysis. The social network was based on spatial proximity data. There was no significant influence of relatedness on strength of associations in the network or an influence of age- or rank-homophily. We argue that the lack of a relatedness effect is not likely to have been caused by an inability to detect kinship. Strength of associations in the social network was significantly affected by the tendency of the horses to associate with individuals of the same sex and the same reproductive state. This social network pattern is not common in mammals, and the study of unexplained variation in choice and strength of associations may have important implications for other equids increasingly confined to reserves worldwide.

Keywords:

• long-term affiliation
• female defense polygyny
• proximity
• kin detection
• feral horses

Acknowledgements

ARK Nature, and in particular, Renee Meissner provided logistic support and vital information. Utrecht Landscape Foundation issued the permit to conduct the study in the Blauwe Kamer Nature Reserve, and Frans Schut provided a lot of assistance at the reserve. For assistance during the observations in the field, we thank Francisca Meijsser, Ruth Bouskila, Arthur du Mosch and Sarah Aamidor. Yael Bogin and Maya Gershoni assisted in the review of the video footage. We thank Amiyaal Ilany, Gili Greenbaum, Shai Pilosof and Mariano Cuadrado for useful discussions and suggestions. Juan Pablo Gutiérrez García provided vital information that enabled the use of ENDOG. We thank Maggie J. Watson and two anonymous reviewers for helpful comments on previous versions of the manuscript.

The collection of data for this study took place during a sabbatical of A. Bouskila from Ben-Gurion University of the Negev to the University of Utrecht, and both universities supported the project and made it possible.

Disclosure statement

No potential conflict of interest was reported by the authors.