Comparison of the social systems of primates and feral horses: data from a newly established horse research site on Serra D’Arga, northern Portugal

Monamie Ringhofer, Sota Inoue, Renata S. Mendonça, Carlos Pereira, Tetsuro Matsuzawa, Satoshi Hirata, Shinya Yamamoto
DOI: 10.1007/s10329-017-0614-y
We revived studies on society of feral horses, which had been initiated by the pioneer of primatology, Kinji Imanishi, but soon subsided without full investigation. Horses form a stable bisexual social group, which is unique in ungulates but similar to primates. Comparative studies between primates and horses are important to better understand the evolution of animal societies; unfortunately, however, fewer studies addressed the social system of feral horses compared to primates. We established a new research site in Serra D'Arga, northern Portugal, then identified 208 individuals of 26 feral horse groups and collected the socioecological data. We found that hypotheses based on primate societies cannot adequately explain the social system of horses, particularly the single-male/multi-male group dichotomy. The comparatively fluctuating male-female relationship in feral horses may highlight the difference between horses' and primates' societies. This study shows that the comparison between primates and non-primates like horses is promising for better understanding of the evolutionary mechanisms underlying social systems of group-living animals.


Horses are phylogenetically distant from primates, but considerable behavioral links exist between the two. The sociality of horses, characterized by group stability, is similar to that of primates, but different from that of many other ungulates. Although horses and primates are good models for exploring the evolution of societies in human and non-human animals, fewer studies have been conducted on the social system of horses than primates. Here, we investigated the social system of feral horses, particularly the determinant factors of single-male/multi-male group dichotomy, in light of hypotheses derived from studies of primate societies. Socioecological data from 26 groups comprising 208 feral horses on Serra D'Arga, northern Portugal suggest that these primate-based hypotheses cannot adequately explain the social system of horses. In view of the sympatric existence of multi- and single-male groups, and the frequent intergroup transfers and promiscuous mating of females with males of different groups, male–female relationships of horses appear to differ from those of polygynous primates.


Polygyny, Single-male/multi-male dichotomy, Society, Group-living animals, Sexual conflict,

Article Information
Ringhofer M, Inoue S, Mendonça RS. , Pereira C, Matsuzawa T, Hirata S, Yamamoto S(2017)Comparison of the social systems of primates and feral horses: data from a newly established horse research site on Serra D’Arga, northern Portugal Primates, Volume 58, Issue 4, pp 479-484.