Influences of Mating Group Composition on the Behavioral Time-Budget of Male and Female Alpine Ibex (Capra ibex) during the Rut

Viblanc VA (2014) Influences of Mating Group Composition on the Behavioral Time-Budget of Male and Female Alpine Ibex (Capra ibex) during the Rut. PLoS ONE 9(1): e86004. doi:10.1371/journal.pone.0086004 Influences of Mating Group Composition on the Behavioral Time-Budget of Male and Female Alpine Ibex (Capra ibex ) during the Rut Federico Tettamanti 0 Vincent A. Viblanc 0 Marco Festa-Bianchet, Universite de Sherbrooke, Canada 0 1 Department of Science for Nature and Environmental Resources, University of Sassari , Sassari , Italy , 2 Centre d'Ecologie Fonctionnelle et Evolutive , Equipe Ecologie Comportementale , Unite Mixte de Recherche 5175, Centre National de la Recherche Scientifique, Universite Montpellier 2 , Montpellier , France During the rut, polygynous ungulates gather in mixed groups of individuals of different sex and age. Group social composition, which may vary on a daily basis, is likely to have strong influences on individual's time-budget, with emerging properties at the group-level. To date, few studies have considered the influence of group composition on male and female behavioral time budget in mating groups. Focusing on a wild population of Alpine ibex, we investigated the influence of group composition (adult sex ratio, the proportion of dominant to subordinate males, and group size) on three behavioral axes obtained by Principal Components Analysis, describing male and female group time-budget. For both sexes, the first behavioral axis discerned a trade-off between grazing and standing/vigilance behavior. In females, group vigilance behavior increased with increasingly male-biased sex ratio, whereas in males, the effect of adult sex ratio on standing/vigilance behavior depended on the relative proportion of dominant males in the mating group. The second axis characterized courtship and male-male agonistic behavior in males, and moving and male-directed agonistic behavior in females. Mating group composition did not substantially influence this axis in males. However, moving and male-directed agonistic behavior increased at highly biased sex ratios (quadratic effect) in females. Finally, the third axis highlighted a trade-off between moving and lying behavior in males, and distinguished moving and female-female agonistic behavior from lying behavior in females. For males, those behaviors were influenced by a complex interaction between group size and adult sex ratio, whereas in females, moving and female-female agonistic behaviors increased in a quadratic fashion at highly biased sex ratios, and also increased with increasing group size. Our results reveal complex behavioral trade-offs depending on group composition in the Alpine ibex, and emphasize the importance of social factors in influencing behavioral time-budgets of wild ungulates during the rut. - Funding: Field accommodation was provided by the Swiss National Park (Forschungskommission des Schweizerisches Nationalparks). FT was the recipient of a PhD scholarship from the University of Sassari. VAV was supported by a post-doctoral fellowship from the AXA Research Fund during the time of writing. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Many vertebrate species, such as polygynous ungulates, exhibit strict sexual segregation during a large part of the year, gathering only for mating [13]. During the reproductive season however, the formation of mixed groups (hereafter mating groups) enables individuals of different sex, age, experience and behavior to cooccur [28]. Because individuals may only allocate a finite amount of time to their daily activities, behavioral trade-offs brought about by social factors, such as mating group composition, may have significant consequences on individual fitness [5,7]. In mating groups, important social factors that affect male and female behavioral time budgets and fitness include group size, adult sex ratio, and group member experience or age [5,711]. For instance, biases in the sex ratio of mature adults (the operational sex ratio [11,12]) may affect competition for available mates, with strong consequences on individual and group behavior [78,11]. Similarly, individuals of different age are likely to differ in their body size and social rank [1317], which in males is often strongly associated with fighting abilities and reproductive success [78,10,13,16]. Thus, the age structure of males within mating groups, and especially the relative proportion of males of high vs. low social rank, is likely to have strong consequences on overall group behavior. Ultimately, by affecting the behavior of males and females, social factors may shape group stability and affect individual fitness [8,18]. Hence, there is a need to refine our understanding of the proximate effects social factors have on ungulate behavior in mating groups, and how variability in the social composition of mating groups influences individual behavior, with emergent properties at the group level [19]. As most ungulates, Alpine ibex (Capra ibex) show strong sexual segregation during a large part of the year, but form mixed sex/ age groups during the rut [4,2021]. Over the course of the reproductive season, ibex exhibit a fission-fusion social system allowing individuals to freely join or leave any given mating group [22]. During the rut, male ibex significantly reduce the amount of time spent foraging and lying to the benefit of mating-related activities, whereas females typically decrease the amount of time Intra-sexual agonistic behavior Inter-sexual agonistic behavior NA Time budgets are calculated within the 45 different mating groups and averaged (see Methods). Columns not sharing the same superscript are different for P,0.05 (Wilcoxon tests). doi:10.1371/journal.pone.0086004.t001 spent lying to the benefit of moving, standing and social activities [23]. Although the rut is generally considered highly energydemanding for male ungulates [2324], male-male agonistic behavior is surprisingly low in the Alpine ibex, owing to a prerut establishment of dominance hierarchies and the use of alternative mating tactics in dominant and subordinate individuals [13,15,22,25]. Thus, in addition to adult sex ratio (and mate availability), the proportion of old to young males that differ in dominance rank in mating groups [13] is likely to strongly influence individual behavior, with emergent properties on male and female group behavior. Further, trade-offs between different activities (e.g. maintenance vs. agonistic behavior) are also likely to vary depending on group member composition. For instance one might expect subordinate males to invest more time into courtship behavior when group sex ratio is biased towards females, and/or when the ratio of dominant to subordinate individuals in a group is low. The aim of this study w (...truncated)