Quantifying animal’s vigilance and exploring the underlying mechanism can help us to understand how animals respond to potential threats and how to balance the tradeoff with other important behaviors. But, as pointed out by Gilbert Roberts: The ‘group-size effect’, a reduction in individual vigilance as group size increases, is one of the most widely reported findings in animal behaviour. However, there was concern expressed that studies had failed to take into account various confounding effects.

Przewalski’s gazelle, Procapra przewalskii, endemic to the Qinghai-Tibetan Plateau, China, is the most endangered antelope species in the grasslands of Asia. In the winter 2008-2009 and the summer 2009, researchers of the Wildlife and Behavioral Ecology group carried out field studies to quantify the vigilance pattern of Przewalski’s gazelle and examine the effects of reproductive status, social rank, sex and group size. We found complex interplay between these factors in determining the vigilance pattern in this species. Individual 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. Together with one of our previous studies (Li et al. 2009), we quantified the vigilance pattern of Przewalski’s gazelle and the underlying influencing factors including sex, group size, predation pressure, reproductive status and social rank.

The finding was published in recent in recent issue of PLoS One（Li C, Jiang Z, Li L, Li Z, Fang H, Li C & Beauchamp G. 2012. Effects of Reproductive Status, Social Rank, Sex and Group Size on Vigilance Patterns in Przewalski's Gazelle. PLoS ONE 7(2): e32607. doi:10.1371/journal.pone.0032607）