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1 July 2010 Survival, Mortality, and Predators of Red Tree Voles (Arborimus longicaudus)
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Although estimations of vital rates are important to understand population dynamics of small mammals, there is little information on survival rates and causes of mortality for many species. In 2002–2003, we estimated monthly and annual survival of 50 radiocollared red tree voles (Arborimus longicaudus) during a study of movements and diel activity patterns in western Oregon. Estimated annual survival for both sexes combined was 0.15 (95% CI = 0.06 to 0.31) and was influenced little by mass at initial capture. In the analysis of explanatory variables, we did not find strong effects of gender, vole age, or forest age on survival. We suspect this may have been due to small sample size and low power to detect effects, because some of the point estimates were suggestive of large differences among groups. Most mortality was due to predation, with 15 of 25 deaths attributed to weasels (Mustela spp.). Weasels preyed upon significantly more females than males (14:1, respectively). Other confirmed or suspected predators were owls (n = 3), a gopher snake (Pituophis catenifer), and a domestic dog (Canis familiaris). Although our results did not support the hypothesis that survival of tree voles was higher in old forests than in young forests, we caution that our sample for this comparison was small and recommend that more definitive studies with larger samples be conducted to better elucidate relationships between vital rates of tree voles and forest age and structure.
James K. Swingle, Eric D. Forsman and Robert G. Anthony "Survival, Mortality, and Predators of Red Tree Voles (Arborimus longicaudus)," Northwest Science 84(3), (1 July 2010).
Received: 6 November 2009; Accepted: 1 May 2010; Published: 1 July 2010

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