However, the detailed structure of this society (e.g., the bonds between harems leading to herd formation) remains unclear.Ī commonly used approach in the study of social structures is the analysis of social networks, where the links between individuals are traditionally quantified by numerous direct observations of social interactions over a long period of time 31, 32. In Hortobágy National Park, Hungary, where the largest captive population of Przewalski’s horses lives in a 3000-ha fenced but otherwise natural habitat, both cases were observed: in the first years after introduction harems had non-overlapping home ranges, while recently the population forms a massive multilevel herd 14. Previous observations show variation in the occurrence of higher-level social units in Przewalski’s horses: harems are observed to live isolated in almost exclusive home ranges in Hustai National Park 29, while in other populations they aggregate and form multilevel herds 14, 24, 30. Another type of social groups are the single-sex bachelor groups formed by non-breeding adult males 27, 28. The mating system of Przewalski’s horses is female defence polygyny, where year-round stable harems are the core units of the society, and the harem’s single breeding male (the harem stallion) protects the adult females and their juvenile offspring belonging to the harem 11, 25, 26, 27. One such taxon where multilevel social organisation can occur is the Przewalski’s horse ( Equus ferus przewalskii) 14, 24, which is the last extant subspecies of wild horses ( Equus ferus). Moreover, the vast majority of human social systems show multilevel structure as well 16, 17, 18, 19, 20, thus studying multilevel societies can fundamentally contribute to our understanding of the evolution of sociality 2, 21, 22, 23. They are best known from primates 3, 4, 5, 6, 7, but are also found in cetaceans 8, 9, elephants 10, equids 11, 12, 13, 14, and birds 15. Individuals in these societies aggregate through multiple nested levels 2: the core units (the lowest social level) are usually breeding units (e.g., one-male, multifemale groups), and higher levels of social organisation are formed by the aggregation of lower-level units. Multilevel societies are arguably among the most complex forms of social organisation in nature 1, 2. Understanding social structure and dynamics of animal societies is an important task in which utilising emerging technologies and high-throughput methods could be the key. Our results show that only a few minutes of fine-scale movement tracking combined with high throughput data driven analysis can reveal the structure of a society, reconstruct past group dynamics and predict future ones. High movement similarity of females from different harems predicts becoming harem mates in the future. Harems of genetically related stallions are closer to each other in the network, and female exchange is more frequent between closer harems. The network centrality of harems is related to their age and how long the harem stallions have kept harems previously. Analysis of collective movements reveals how the structure of the herd’s social network is related to kinship and familiarity of individuals. We track, in high spatio-temporal resolution, the movements of 238 individually identified horses on drone videos, and combine movement analyses with demographic data from two decades of population monitoring. Here, we present a state-of-the-art drone observation of a multilevel herd of Przewalski’s horses, consisting of harems (one-male, multifemale groups). Studying animal societies needs detailed observation of many individuals, but technological advances offer new opportunities in this field.
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