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Flauger, B., & Krueger, K. (2012). Social feeding decisions in horses (Equus caballus). In Proceedings of the 2. International Equine Science Meeting (Vol. in press). Wald: Xenophon Publishing.
Abstract: Like many other herbivores equids feed on rather evenly distributed resources. Especially in ruminants several studies have proved the influence of social organisations, rank, sex and the depletion of feeding sites on the feeding behaviour of individuals. However, it is not yet understood whether social aspects affect horses´ feeding decisions. Horses roam on vast habitats with constantly changing vegetation. In non-competitive situations domestic horses tend to return to the same feeding site until it is overgrazed. Whereas, for competition over limited food the social status of the individuals appears to be important. Curiosity about the influence of social rank and different social feeding conditions on the horses´ feeding decisions between two buckets, equally filled with high-quality surplus food, led us to create the test situation described here. The observer horses were alternately tested with a dominant and a subordinate demonstrator placed in one of three different positions. We conclude that domestic horses use cognitive strategic decision making in order to decide where to feed in a social feeding situation. When possible they tend to return to the same, continuously supplied feeding site and switch to an “avoidance tendency” when another horse is already feeding from it or in the presence of a dominant horse. Thus the position and the social rank of conspecifics affect the feeding strategy of horses.
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Wolter, R., & Krueger, K. (2015). The analysis of social bonds in feral horses. In Proceedings of the 3. International Equine Science Meeting.
Abstract: In many social mammals, individuals preferentially affiliate with a small subset of available partners instead of distributing their social behaviors equally among all group members. The resulting social bonds have been investigated in several mammalian taxa, especially in primate societies, but also in other taxa such as birds, dolphins, rodents and ungulates. In feral horses, a great number of studies on social bonds can be found, but with a huge variety between methods for the analysis. There seems to be a lack of a clear and common definition of social bonds in horses and of comparable analyses. For example, there are irregularities between the studies regarding the research designs, the selection of recording methods and the interpretation of the measurements. Mutual grooming is used most often for the analysis of social relationships in many species. As mutual grooming is rare in horses, especially measurements of spatial proximity are commonly used for the analysis of social bonds in addition to other behavioral patterns. However, the combination of mutual grooming and nearest neighborhood analyses for the analysis of social bond is debatable, as in contrast to mutual grooming, which must occur deliberately by both grooming partners, the spatial distribution can be influenced by one partner alone, which may even force the other horse to keep a certain distance or to stay in close proximity.
In this study, we investigated the comparability of mutual grooming and nearest neighborhood data for social bond analyses in feral horses. Therefore, we observed five groups of semi-wild living Przewalski’s horses and six groups of feral horses.
We analysed the horses’ social ranks by applying an Average Dominance Index, we recorded the distances between the animals and observed the number of mutual grooming events as well as friendly approaches.
Our results show that there was only a weak correlation between the frequency of staying in nearest neighborhood and mutual grooming in all observed horse groups. In contrast to this, the correlation between the number of friendly approaches and mutual grooming events was higher in most groups.
Hierarchies did not affect social bonds, as mutual grooming was similarly induced by higher and lower ranking animals and the social rank did not affect the choice of the grooming partner. Similarly, likelihoods of staying in the neighborhood of particular animals were not affected by the animals’ social rank.
The grooming frequencies differed between the different horse groups and between the individual horses living in the particular groups. They seem to be effected by individual predisposition.
Altogether we suggest that the ratio of mutual grooming seems to be a better indicator for social bonds in feral horses than the frequency of staying in the nearest neighborhood. Mutual grooming occurs deliberately and is bidirectional, whereas nearest neighborhoods could be enforced and unidirectional. For the calculation of social bonds in horses, we consider it to be more reliable to combine the frequency of mutual grooming with the frequency of friendly approaches.
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Creel, S. (2001). Social dominance and stress hormones. Trends. Ecol. Evol, 16(9), 491–497.
Abstract: In most cooperatively breeding birds and mammals, reproductive rates are lower for social subordinates than for dominants, and it is common for reproduction in subordinates to be completely suppressed. Early research conducted in captivity showed that losing fights can increase glucocorticoid (GC) secretion, a general response to stress. Because GCs can suppress reproduction, it has been widely argued that chronic stress might underlie reproductive suppression of social subordinates in cooperative breeders. Contradicting this hypothesis, recent studies of cooperative breeders in the wild show that dominant individuals have elevated GCs more often than do subordinates. The findings that elevated GCs can be a consequence of subordination or a cost of dominance complicate the conventional view of social stress, with broad ramifications for the evolution of dominance and reproductive suppression.
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Keil, N. M., Sambraus, H.H. (1998). “Intervenors” in agonistic interactions amongst domesticated goats. Z. Säugetierk., 63(5), 266–272.
Abstract: Social behaviour was observed in individually marked goats in two herds. The goats from one herd (n = 98) were horned, those of the other herd (n = 83) were polled. By recording agonistic interactions within the herds, a dominance index was determined for each animal. In both herds, intervention took place. Intervention is defined as one animal pushing in between two fighters, and thus ending the fight. More cases of intervention took place per individual animal amongst the horned goats than amongst the polled ones. Goats which intervened in fights on several occasions usually had a high dominance index. Members of the herd which were observed intervening only once had an average dominance index in both herds of almost 0.5. In some cases, goats very low in the rank order intervened a fight. Only rarely did the intervenors have a lower dominance index than the two fighters. In 103 cases, the direct dominance relationship between a fighting animal and the intervenor was known. In 95 cases (92.2%), the intervenor was dominant to the herd member in this fight and in just eight cases (7.8%), it was subordinate. It could not be determined what advantage the intervenor gained from its activity. It is possible that, at least in certain cases, a particularly relationship existed between the intervenor and one of the fighters.
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