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

We used giving-up densities in food patches to measure the effectsof several direct (left by the predator) and indirect (environmentalcorrelates of risk) cues of predatory risk on the foraging behaviorof free-living fox squirrels (Sciurus niger) and thirteen-linedground squirrels (Spermophihis tridtctmlineatus). Increasesin giving-up density in response to stimuli allow quantitativecomparisons of the effects of different types of cues. We usedolfactory (urine of red fox) and visual (plastic models of owls)direct cues. As indirect cues, we used mkrohabitat (near orfar from a refuge), background coloration (white, green, andbrown tarpaulins), and escape substrate (canvas tarpaulins versusnatural surrounding substrates). Both squirrel species respondedmost strongly to microhabitat Fox squirrels increased theirgiving-up density by 97% when feeding 4–6 m from a treecompared to feeding at the tree base. Thirteen-lined groundsquirrels increased giving-up densities 84% when feeding 2 mfrom their burrows compared to feeding at the burrow entry.In response to an unfavorable escape substrate (canvas versusgrass), fox squirrel giving-up densities increased 61%. Foxsquirrels and ground squirrels increased giving-up densities26% and 35%, respectively, in response to a plastic owL Backgroundcoloration had no demonstrable effect on the giving-up densitiesof fox squirrels. In contrast to other work on nocturnal mammalianherbivores and granivores, the diurnal fox squirrels did notrespond to olfactory cues.