The findings show that wild horses, like humans, live in a complex, multi-layered society. Using high-definition aerial footage can decipher organizational structures and even past and future group dynamics. Researchers from the Hungarian Research Network (HUN-REN), the University of Debrecen (UD), Eötvös Lorand University (ELTE) and the Hortobágy National Park Authority studied the social dynamics of the Hortobágy Przewalski horse herd. They use drone technology combined with extensive population monitoring data for analysis.
By deploying two drones, the team carefully monitored the movements of 278 Przewalski's horses at high temporal and spatial resolution, while identifying most of the animals individually. The results show that wild horses, like humans, live in a complex, multi-layered society whose structure and even past and future changes in the population can be understood with the help of high-resolution aerial video.
A paper describing this research was published in the prestigious scientific journal Nature Communications.
A harem of Przewalski's horses gather together to form a large, multi-layered herd in Hortobágy National Park, Hungary. Each harem consists of one male (the harem stallion) and several females and their young offspring. Image credit: Katalin Ozogány
Investigating the social behavior of a large group of animals is a time-consuming endeavor using classic observational methods. However, research published in Nature Communications highlights that by collecting high-resolution data, even a few minutes of footage of an animal's movement can provide enough information to understand the social structure of a population and even draw conclusions about an animal's past and future dynamics.
"We wanted to investigate the group activities of a herd of Przewalski's horses in Hortoba, Hungary. However, observing nearly 300 horses at the same time is not an easy task," says Katalin Ozogány, first author of the study and member of the Hungarian Research Network and the HUN-REN-UD Behavioral Ecology Research Group at the University of Hungary. “We used drones to capture aerial video of the horses as they moved around the reserve, and based on the footage, we identified the movement routes of all individuals in the herd with high spatiotemporal resolution.”
Multi-layered social structures are also characteristic of humans, which are rare among animals. It occurs primarily in primates but also in cetaceans, elephants, and some ungulates, where individuals form smaller family groups (e.g., a harem or a group of related females led by a matriarch), and these family groups form larger, looser communities.
Przewalski's horses have been living in the Pentezug reserve in Hortobágy since 1997. During the first few years after forming a colony, harems of wild horses live in their own territories and rarely interact with each other. However, over a dozen years, the harems formed together a large herd, in which the harems were still distinguishable, but they moved together in the reserve. The researchers studied the group movements of this complex harem of cattle.
Analysis of horse herd activity by members of the “Lendület” research group on collective behavior at the Hungarian Academy of Sciences and Eötvös Loránd University (Hungary) produced surprising results. "Individuals in a swarm coordinate their actions and cooperate with each other, and by detecting these fine-grained interactions between individuals, it turns out that we can assess the social network of a swarm based on its movements," explains Máté Nagy, lead author of the study.
Researchers combined a few minutes of short-term activity observations with long-term population monitoring data from the national park dating back two decades. Since the reserve's establishment, wild horses have been individually recognized by park staff and data on population changes have been regularly collected. "Through population monitoring we know the ancestry of the animals, which we also confirm through genetic sampling, as well as their position in the social system, that is, we regularly record which individual belongs to which harem," says co-author Viola Kerekes, project leader at the Hortobágy National Park Service.
Analysis shows that social relationships in wild horses are related to kinship and familiarity with the animals. For example, if mares have been harem mates for a longer period of time, they will be more closely related in their social network.
Kinship may play an important role in the organization of harems into herds, as harems of sibling stallions (single breeding males in a harem) are closer to each other in social networks than harems of unrelated stallions. At the same time, there is greater dispersion of mares between harems that are closer together, which also promotes relationships between harems through familiarity.
"This is an excellent opportunity to explore social networks and their dynamics across entire populations," explains co-author Attila Fülöp, researcher at the Behavioral Ecology Research Group at Babeş-Bolyai University (Romania) and HUN-REN-UD. It turns out that older, larger harems often belong to older, more experienced stallions who occupy a more central position in the herd's social network. One possible explanation is that harem stallions form alliances to more effectively protect their harems from single males.
"A surprising result of this study is that we can infer future group dynamics by observing current movements," adds lead author Zoltán Barta, Head of the Department of Evolutionary Zoology and the Department of Ethology at HUN-REN-UD at the University of Debrecen.
The researchers showed that mares that were living in different harems at the time of aerial observation but became harem partners within two years of observation were already following more similar routes than other mares. Therefore, through movement analysis, it is also possible to deduce which mares will leave the harem and transfer to which harem in the next two years.
"Not only did we learn new, previously unknown details about the social life of Przewalski's horses, but we highlight that drone observations can even be applied to wild populations and can provide very detailed information."