Northern range boundary dynamics of southern flying squirrels: evidence of an energetic bottleneck

Abstract

We undertook a large-scale survey of the distribution of northern, Glaucomys sabrinus (Shaw, 1801), and southern, Glaucomys volans (L., 1758), flying squirrels in Ontario, Canada. Livetrapping was conducted along a north–south transect spanning about 500 km, from 42.5°N to 47.2°N. During 2002–2004, we conducted 42 971 trap-nights at 26 sites and captured 232 northern and 538 southern flying squirrels. During 2002 and 2003, southern flying squirrels occurred >200 km farther north than we expected. However, the range of this species appeared to contract to the south by about 240 km after the winter of 2004. Weather and food data suggested that cold temperatures during January and February 2004 combined with a failed mast crop in the autumn of 2003 resulted in an energetic bottleneck and subsequent population crash. We speculate that prior to 2004 southern flying squirrels had expanded their geographic range in response to recent climate warming. In particular, the nine winters between 1994 and 2004 were relatively warm. By measuring the range expansion over this warm interval, we were able to estimate a rate of spread of 22 km per year, and a diffusion coefficient of 6.9 × 107 m2 per generation.