Seasonal changes in nest use of Japanese squirrels in a suburban forest in Morioka City

Abstract

We investigated the nest use of Japanese squirrels (Sciurus lis) via radio-tracking in a suburban forest of Morioka City, Iwate Prefecture, northeastern Japan, from April to December 2010, July to October 2012 and May 2013 to July 2014. Squirrels frequently used dreys on evergreen trees all year round. Dreys were widely used in green-leaved seasons, and cavities were comparably used in both seasons. In addition, home range and nest site movement distance (straight line distance between nest locations prior to and after nest changes) were larger for males than for females. Nest site movement distance (mean ± SD) for females was 68 ± 42 m in the green-leaved season, and 82 ± 42 m in the defoliated season. That of males was 115 ± 59 m in the green-leaved season, and 135 ± 71 m in the defoliated season. The average distance of the closest approach from a nest to a walnut tree was 37.4 ± 33.3 m for males, and 30.5 ± 22.2 m for females. Squirrel movement appeared to reduce predator risk while efficiently using food resources, suggesting seasonal food use adaptation.