Variation in the echolocation calls of the hoary bat (Lasiurus cinereus):: influence of body size, habitat structure, and geographic location

The echolocation calls of bats vary according to the task being undertaken by the individual. Within species, there is evidence for geographic, habitat, and individual variation, although it is often difficult to separate these factors and rule our variation in recording or analysis techniques. We studied the variation in echolocation call design of the hoary bat (Lasiurus cinereus) by analyzing calls, recorded in the same manner, from free-flying bats at one site in Manitoba and at four sites in the Hawaiian islands. Sites varied in terms of the proximity of the bats to vegetation. As predicted, individuals from the lager subspecies (Lasiurus cinereus cinereus; Manitoba) used lower frequency calls than did the smaller individuals in Hawai'i. Within the same habitat type (open or closed), there was evidence for differences in echolocation call design between populations on different islands. On the island of Hawai'i, bats at a single site used shorter higher frequency calls when foraging within the vegetation than when foraging in the open, again as predicted. However, bats foraging in different sites used calls with the opposite characteristics to those predicted on the basis of the openness of the site. Although there are several possible explanations for this, we suggest that prey encounter rate and the ability of bats to augment acoustic prey detection with visual information may be important.