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| Photo: Katalin Ozagány |
(UD), Eötvös Loránd University (ELTE), and the Hortobágy National Park Directorate studied the social system of the Przewalski's horse herd in Hortobágy. The research involved a combination of drone-based movement analysis and long-term population monitoring data.
The researchers used drones to monitor the 278 Przewalski's horses, individually identifying most of them, and found that these wild horses, like humans, live in a complex, multilevel society. They used high-resolution aerial videos to understand the structure of this society and its past and future group changes.
The research is published in the scientific journal Nature Communications.
Studying the social behaviour of a large group of animals using traditional methods is time-consuming. Nevertheless, this study shows that collecting high-resolution data, even just a few minutes of animal movement footage, can yield sufficient information to understand the population's social structure and make predictions about its past and future dynamics.
"We wanted to investigate the group movements of the Przewalski’s horse herd in Hortobágy, Hungary. However, observing nearly 300 horses at the same time is not an easy task," says Katalin Ozogány, the first author of the study, member of the HUN-REN–UD Behavioural Ecology Research Group of the Hungarian Research Network and the University of Debrecen (Hungary).
"We took aerial videos of the herd using drones while they were moving around the reserve, and based on the footage, we determined the movement routes of all the individuals of the herd with high spatio-temporal resolution."
They used two drones to record the herd’s movements. One recorded a wide-angle view to track the movement of all individuals in the herd. A second drone scanned through the herd providing close-up views to allow identification of individual animals.
In the past, wild horses ranged across the vast expanses of the Eurasian steppes, but today, they are confined to just a few national parks. The Przewalski's horse, classified as endangered, represents the sole surviving sub-species, with a worldwide population numbering less than 3,000 individuals.
Przewalski’s horses have been living in Hortobágy since 1997, in the Pentezug reserve. In the first years after founding the population, the harems (each consisting of a stallion and a group of breeding mares) lived in their own home ranges and rarely interacted with each other. Now, for over a decade, the harems have grouped together to form a large herd, in which harems can still be distinguished, but they move together in the reserve.
Such a multilevel social structure, characteristic of humans, is uncommon in animals. It is mainly found in primates, but also occurs in cetaceans, elephants, and some ungulates.
Analysis of the herd’s movements yielded surprising results. "The individuals of the group coordinate their movements and align with each other, and by detecting these fine interactions between the individuals, it turned out that we can assess the herd's social network based on the group movements," explains lead author Máté Nagy, head of the Collective Behaviour 'Lendület' Research Group of the Hungarian Academy of Sciences and Eötvös Loránd University (Hungary).
The researchers combined the short-term movement observations of a few minutes with long-term population data going back two decades. allowing them to reconstruct the development of the harem groups over more than 20 years.
Since the establishment of the reserve, the wild horses have been individually recognized by the park staff who regularly collected data on population changes. "Thanks to population monitoring, we know the parentage of the animals, which we also confirm with genetic sampling, as well as their place in the social system, that is, we regularly record which individual belongs to which harem," says co-author Viola Kerekes, project leader of the Hortobágy National Park Directorate.
The analyses showed that the social relations of wild horses are related to kinship and familiarity of the animals. For example, mares are closer to each other in the social network if they have been harem mates for a longer time. Kinship may play a significant role in the organization of harems into herds since harems of sibling stallions are closer to each other in the social network than harems of unrelated stallions. Between the closer harems, at the same time, the dispersal of mares was greater, which also contributes to the relations between harems through familiarity.
"It is an exceptional opportunity to explore the social network of an entire population and its dynamics," explains co-author Attila Fülöp, a researcher at the Babeş-Bolyai University (Romania) and the HUN-REN–UD Behavioural Ecology Research Group. It turned out that older and larger harems, which typically belong to older and more experienced stallions, occupy more central locations in the herd’s social network. A possible explanation is that harem stallions form an alliance to protect their harems more effectively against the bachelor males. Harems moved as cohesive units within the herd, while bachelor males were typically found on the outer margins of the herd.
"One of the surprising outcomes of the study is that we can infer future group dynamics by observing current movement," adds Zoltán Barta, lead author, head of the Department of Evolutionary Zoology of the University of Debrecen and the HUN-REN–UD Behavioural Ecology Research Group. The researchers showed that mares that lived in different harems at the time of the aerial observations but became harem mates within two years after the observations, were already moving in more similar routes than the other mares. So, through the movement analysis, it was also possible to conclude which mares will leave their harem in the next two years and which harem they will transfer to.
"Not only did we learn new, previously unknown details about the social life of Przewalski's horses, but we highlighted that drone observations, which can be applied even in wild populations, can provide very detailed information."
For more details, see:
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
Nature Communications (2023) vol 14, Article number: 5096 (2023)
https://doi.org/10.1038/s41467-023-40523-3
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