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Selva, N., Cortés-Avizanda, A., Lemus, J. A., Blanco, G., Mueller, T., Heinrich, B., et al. Stress associated with group living in a long-lived bird. Biol Lett, .
Abstract: Many long-lived avian species adopt life strategies that involve a gregarious way of life at juvenile and sub-adult stages and territoriality during adulthood. However, the potential associated costs of these life styles, such as stress, are poorly understood. We examined the effects of group living, sex and parasite load on the baseline concentration of faecal stress hormone (corticosterone) metabolites in a wild population of common ravens (Corvus corax). Corticosterone concentrations were significantly higher in non-breeding gregarious ravens than in territorial adults. Among territorial birds, males showed higher stress levels than their mates. Parasite burdens did not affect hormone levels. Our results suggest a key role of the social context in the stress profiles of the two population fractions, and that group living may be more energetically demanding than maintaining a territory. These findings have implications for understanding hormonal mechanisms under different life styles and may inspire further research on the link between hormone levels and selective pressures modulating gregarious and territorial strategies in long-lived birds.
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Sibbald, A. M., Elston, D. A., Smith, D. J. F., & Erhard, H. W. (2005). A method for assessing the relative sociability of individuals within groups: an example with grazing sheep. Appl. Anim. Behav. Sci., 91(1-2), 57–73.
Abstract: We describe a method for quantifying relative sociability within a group of animals, which is defined as the tendency to be close to others within the group and based on the identification of nearest neighbours. The method is suitable for groups of animals in which all individuals are visible and identifiable and has application as a tool in other areas of behavioural research. A sociability index (SI) is calculated, which is equivalent to the relative proportion of time that an individual spends as the nearest neighbour of other animals in the group and is scaled to have an expectation of 1.0 under the null hypothesis of random mixing. Associated pairs, which are animals seen as nearest neighbours more often than would be expected by chance, are also identified. The method tests for consistency across a number of independent observation periods, by comparison with values obtained from simulations in which animal identities are randomised between observation periods. An experiment is described in which 8 groups of 7 grazing sheep were each observed for a total of 10, one-hour periods and the identities and distances away of the 3 nearest neighbours of each focal animal recorded at 5-min intervals. Significant within-group differences in SIs were found in four of the groups (P < 0.001). SIs calculated using the nearest neighbour, two nearest neighbours or three nearest neighbours, were generally highly correlated within all groups, with little change in the ranking of animals. There were significant negative correlations between SIs and nearest neighbour distances in five of the groups. It was concluded that there was no advantage in recording more than one neighbour to calculate the SI. Advantages of the SI over other methods for measuring sociability and pair-wise associations are discussed.
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Traversa, D., Otranto, D., Iorio, R., & Giangaspero, A. (2005). Molecular characterization of Thelazia lacrymalis (Nematoda, Spirurida) affecting equids: a tool for vector identification. Mol Cell Probes, 19(4), 245–249.
Abstract: Equine thelaziosis caused by the eyeworm Thelazia lacrymalis is a parasitic disease transmitted by muscid flies. Although equine thelaziosis is known to have worldwide distribution, information on the epidemiology and presence of the intermediate hosts of T. lacrymalis is lacking. In the present work, a PCR-RFLP based assay on the first and/or second internal transcribed spacer (ITS1 and ITS2) of ribosomal DNA was developed for the detection of T. lacrymalis DNA in its putative vector(s). The sensitivity of the technique was also assessed. The restriction patterns obtained readily differentiated T. lacrymalis from four species of Musca (Diptera, Muscidae) (i.e. Musca autumnalis, Musca domestica, Musca larvipara and Musca osiris), which are potential vectors of equine eyeworms. The molecular assay presented herein is a useful tool to identify the intermediate host(s) of T. lacrymalis in natural conditions and to study its/their ecology and epidemiology.
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Vitale, V., Balocchi, R., Varanini, M., Sgorbini, M., Macerata, A., Sighieri, C., et al. (2013). The effects of restriction of movement on the reliability of heart rate variability measurements in the horse (Equus caballus). J. Vet. Behav., 8(5), 400–403.
Abstract: Analysis of heart rate variability (HRV) is a noninvasive approach for investigating the sympathovagal balance of the autonomic nervous system. In recent years, HRV has been increasingly evaluated in animal research. In horses, it has been suggested that basal resting conditions can be achieved by restraining them. The aim of this study was to verify how restriction of movement influences HRV i2n horses. Ten healthy standardbred mares were used to measure the electrocardiographic signal under 2 conditions: free to move in the stall and restrained in the stock. Results indicate that the restriction of movement is associated with increased nervous system sympathetic activity not consistent with resting conditions.
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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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Zenzinger, S. (2010). Experimentelle Untersuchungen zur optischen Kommunikation bei im Zoo gehaltenen Schabracken- und Flachlandtapiren (Tapirus indicus und Tapirus terrestris). Der Zoologische Garten, 79(4-5), 162–174.
Abstract: Until now, unlike their relatives, rhinos and horses tapirs have received considerably less attention in studies about communication. Therefore, it was the aim of this study to test which stimuli contain optical information for tapirs. For this purpose, the reactions of tapirs on optical stimuli (posters with edited tapir silhouettes) were examined. Research visits took place at the zoos of Berlin, Dortmund, Heidelberg, Munich, Nuremberg and Osnabrück during the year 2006. A total of 23 individuals, thereof 8 (5.3) Malayan tapirs (Tapirus indicus) and 15 (5.10) Lowland tapirs (Tapirus terrestris) attended the experiment. The results of the optical test with variously intense edited tapir silhouettes speak for the importance of the white ear rims as a family specific key stimulus. But that effect could not be amplified by adding a greater extent of white to the silhouette. Tapirs of both species reacted most strongly to the normal tapir silhouette followed by a silhouette without proboscis.
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