Elk (Cervus elaphus) vigilance levels in response to predation risk from wolves (Canis lupus)
Liley, Stewart Grayson
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Many studies have shown that levels of antipredator vigilance are sensitive to variation in prey attributes, such as age, sex and group size. It is also well established that vigilance is sensitive to environmental effects, such as the presence of cover. In contrast, little is known about the sensitivity of vigilance to variation in factors associated with the predator itself, such as proximity, the size of the threatening group, and cues about motivation to hunt. Finally, little is known about the relative importance of these three classes of variables (predator, prey, and environment), or about the information content of simple versus complex models of vigilance. We quantified the vigilance levels of elk (Cervus elaphus) preyed upon by wolves (Canis lupus) in Yellowstone National Park, between January and May in 2005 and 2006, and compared a set of 38 regression models for vigilance levels, using Akaike's Information Criterion.Complex models incorporating the characteristics of the wolf pack, the structure of the elk herd, and the environmental conditions performed better than simple models. While univariate models of vigilance detect significant relationships, they have low information content relative to multivariate models. These results show that elk assess factors of several types when assessing risk and deciding how much time to allocate to vigilance. In particular, we found that all well-supported models of vigilance included several 'prey' variables and several 'predator' variables. This result highlights the need to consider information about predators when trying to explain vigilance levels in prey.