Drones used to explore wild horse society

The complex, multi-structured society of wild horses and its changes have been studied using high-resolution aerial imagery by Hungarian researchers, including specialists from the University of Debrecen, in a recently finished multi-year study. The results were recently published in the prestigious international scientific journal Nature Communications.

The researchers used a drone to follow the movements of a complex herd of harem Przewalski's stallions living in the Pentezug reserve in Hortobágy. The study, published in the journal Nature Communications, shows that just a few minutes of high-resolution data can provide enough information to understand the social structure of the population and even draw conclusions about the past and future dynamics of the group.

- Simultaneously observing around three hundred animals is not easy. We used drones to take aerial videos of the studs as they moved around the reserve, and used the images to determine the movement paths of all the individuals of the stud farm with high spatial and temporal resolution," said Katalin Ozogány, a researcher at the University of Debrecen, first author of the study and member of the HUN-REN-DE (formerly ELKH-DE) Behavioural Ecology Research Group.

The analysis of the movement has yielded some surprising results for the researchers,too.

- The animals in the group coordinate their movements, they adapt to each other, and, as it turned out, by detecting these subtle interactions, we can learn about the social network of the animals of the stud farms based on their joint movements," explained lead author Máté Nagy, head of the Group Behaviour 'Lendület /Impetus/' research group at the Hungarian Academy of Sciences (MTA-ELTE).

The researchers compared the short, few-minute observations of movement with two decades of data on population monitoring from the national park. Wild horses have been individually recognized by park staff ever since the reserve was established and data on population changes are regularly collected.

- Due to population monitoring, we know the animals' lineage, which is confirmed by genetic sampling, and their position in the social system, i.e. we regularly record which individual belongs to which harem," said co-author Viola Kerekes, head of the wild horse project at the Hortobágy National Park Directorate.

Analyses have shown that the social relationships of wild horses are linked to kinship and previous acquaintanceship with the animals. Mares, for example, are closer in the social network to mares with whom they have been related for a longer period of time. Kinship may play an important role in the organisation of the harems into a herd, as harems of related stallions are closer to each other in the social network than those of unrelated stallions. At the same time, there was a markedly higher turnover of mares between the closer harems, which also contributes to the links between harems through the familiarity link.

- It is an exceptional opportunity to unravel the social network and its dynamics of an entire population," said co-author Attila Fülöp, researcher at the University of Debrecen, Babeş-Bolyai University and the HUN-REN-DE (former ELKH-DE) Behavioural Ecology Research Group.

It was found that harems with a longer history and more members, typically belonging to older, more experienced stallions are more central in the social network of the herd. One possible explanation for this is that harem stallions form alliances to better protect their harems from bachelor stallions. Movement analysis also allowed us to infer which mares would leave their harem and which harem they would move to in the next two years.
- In a surprising twist to the study, we can also predictfuture group dynamics by observing current movement. The researchers have shown that mares that were living in different harems at the time of the aerial recordings, but became harem mates in the two years following the recording, were already moving on a more similar trajectory than the other mares at the time of the recording," added lead author Zoltán Barta, head of the Department of Evolutionary Zoology at the University of Debrecen and the Behavioural Ecology Research Group of HUN-REN-DE (formerly ELKH-DE).

The study (Fine-scale collective movements reveal present, past and future dynamics of a multilevel society in Przewalski's horses. Katalin Ozogány, Viola Kerekes, Attila Fülöp, Zoltán Barta & Máté Nagy), written by researchers from the University of Debrecen, Eötvös Loránd University and the Hortobágy National Park Directorate, was published on 5 September in Nature Communications. A short video of the paper is available at this link.

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