Abstract
BackgroundQuantifying vigilance and exploring the underlying mechanisms has been the subject of numerous studies. Less attention has focused on the complex interplay between contributing factors such as reproductive status, social rank, sex and group size. Reproductive status and social rank are of particular interest due to their association with mating behavior. Mating activities in rutting season may interfere with typical patterns of vigilance and possibly interact with social rank. In addition, balancing the tradeoff between vigilance and life maintenance may represent a challenge for gregarious ungulate species rutting under harsh winter conditions. We studied vigilance patterns in the endangered Przewalski's gazelle (Procapra przewalskii) during both the rutting and non-rutting seasons to examine these issues.Methodology/Principal FindingsField observations were carried out with focal sampling during rutting and non-rutting season in 2008–2009. Results indicated a complex interplay between reproductive status, social rank, sex and group size in determining vigilance in this species. Vigilance decreased with group size in female but not in male gazelles. Males scanned more frequently and thus spent more time vigilant than females. Compared to non-rutting season, gazelles increased time spent scanning at the expense of bedding in rutting season. During the rutting season, territorial males spent a large proportion of time on rutting activities and were less vigilant than non-territorial males. Although territorial males may share collective risk detection with harem females, we suggest that they are probably more vulnerable to predation because they seemed reluctant to leave rut stands under threats.Conclusions/SignificanceVigilance behavior in Przewalski's gazelle was significantly affected by reproductive status, social rank, sex, group size and their complex interactions. These findings shed light on the mechanisms underlying vigilance patterns and the tradeoff between vigilance and other crucial activities.
Highlights
Vigilance in animals may reduce the likelihood of being attacked and increase fitness by improving the ability to survive, obtain resources, reproduce and protect offspring [1,2]
The final model without social rank revealed a significant effect of sex, reproductive status, group size and an interaction between sex and group size
The independent model to test the effect of social rank indicated that non-territorial males (7.0%60.9%) spent more time scanning than territorial males (1.6%60.2%) during the rutting season (Table S1)
Summary
Vigilance in animals may reduce the likelihood of being attacked and increase fitness by improving the ability to survive, obtain resources, reproduce and protect offspring [1,2]. Vigilance behavior is often performed at the expense of other fitness-enhancing activities crucial for life maintenance and reproduction, such as foraging, resting and mating [3,4]. Quantifying vigilance patterns and exploring underlying influencing factors help us to understand how animals respond to potential threats and balance the tradeoff between vigilance and other crucial activities [5]. While not universal [12], many studies have detected a decrease in individual vigilance in larger groups, which is usually explained by the many-eyes effect, risk dilution or scramble competition [13,14,15]. Mating activities in rutting season may interfere with typical patterns of vigilance and possibly interact with social rank. We studied vigilance patterns in the endangered Przewalski’s gazelle (Procapra przewalskii) during both the rutting and non-rutting seasons to examine these issues
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