PARENT SESSION
Oral Session # 42: Mammal Ecology: From Mice to Elephants.
Presiding: H Howe
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 104.
Effects of seasonality on foraging in urban versus natural squirrel populations.
Burke, Anna1, van der Merwe, Marius1, Brown, Joel1, 1 University of Illinois at Chicago, Chicago, IL
ABSTRACT- In two populations of fox squirrels, Sciurus niger, we measured the effect of seasonality on foraging responses to microhabitat (near and away from cover) and cacheability of food (hazelnuts with or without shells). We chose our populations of squirrels to reflect an urban habitat (Oak Park, IL) and a more natural area (the Morton Arboretum in Lisle, IL). Urban squirrels seem to have two advantages over their natural counterparts; there is more food available and less predation. But these conditions lead to higher squirrel densities in urban areas; meaning urban squirrels should actually be more food limited. We measured giving-up densities (GUDs) of fox squirrels in the two populations of squirrels from Winter 2001 to Fall 2002 to test predictions about the effects of seasonality in the two different locations. We predicted GUDs would be the lowest in winter (when populations are food limited) and highest in the fall (when natural food resources are more abundant), and that urban squirrels would have lower GUDs. Overall, GUDs were approximately 10% higher in summer than in fall and winter. Interestingly, overall GUDs were lower in the Arboretum squirrel population than the urban population by 17% (about one nut per foraging bout), contrary to our predictions. Season had opposite effects on the urban and non-urban squirrels. Oak Park squirrels had their highest GUDs of the three seasons in the summer, while Arboretum squirrels had their lowest GUDs in the summer. We expected urban squirrels to show a stronger preference for cacheable nuts and weaker distinction between safe and risky microhabitats than non-urban squirrels. Urban squirrels did have a stronger preference for cacheable nuts, but they actually showed more of a distinction between microhabitats. Seasonality appears to influence foraging; however, it does not necessarily have similar effects on all squirrel populations.
Key words: squirrels, seasonality, foraging, diet