Direct and indirect cues of predatory risk and patch use by fox squirrels and thirteen-lined ground squirrels

Abstract

We used giving-up densities in food patches to measure the effects of several direct (left by the predator) and indirect (environmental correlates of risk) cues of predatory risk on the foraging behavior of free-living fox squirrels (Saurus nigrt) and thirteen-lined ground squirrels (Spermophihis tridtctm&neatus). Increases in giving-up density in response to stimuli allow quantitative comparisons of the effects of different types of cues. We used olfactory (urine of red fox) and visual (plastic models of owls) direct cues. As indirect cues, we used mkrohabitat (near or far from a refuge), background coloration (white, green, and brown tarpaulins), and escape substrate (canvas tarpaulins versus natural surrounding substrates). Both squirrel species responded most strongly to microhabitat Fox squirrels increased their giving-up density by 97% when feeding 4-6 m from a tree compared to feeding at the tree base. Thirteen-lined ground squirrels increased giving-up densities 84% when feeding 2 m from their burrows compared to feeding at the burrow entry. In response to an unfavorable escape substrate (canvas versus grass), fox squirrel giving-up densities increased 61%. Fox squirrels and ground squirrels increased giving-up densities 26% and 35%, respectively, in response to a plastic owL Background coloration had no demonstrable effect on the giving-up densities of fox squirrels. In contrast to other work on nocturnal mammalian herbivores and granivores, the diurnal fox squirrels did not respond to olfactory cues.