The auditory perception of eight species of raptors was examined to test th
e hypothesis of Marler (1955) that these avian predators are unable to loca
te certain songbird alarm calls. In particular, Marler proposed that mobbin
g calls have characteristics that enhance their locatability and that these
characteristics are absent in the high-frequency 'seet' calls given by ind
ividual songbirds. To test this hypothesis, the behavioral responses of fou
r species of owls and four species of hawks, housed at two different raptor
rehabilitation sites, to tape recorded alarm calls were examined. Each rap
tor was exposed to a random order of 10 trials of mobbing calls and 10 tria
ls of a seet call. Responses were scored based upon head angle orientations
. Hawks and owls responded more often and more accurately to mobbing calls
than to sect calls. In general, owls responded to significantly more calls
than hawks. The results are consistent with Marler's hypothesis that raptor
s have difficulty locating passerine sect calls. Nevertheless, future studi
es should test mobbing calls that vary in their frequency and duration (Fic
ken & Popp 1996) to determine whether some mobbing calls are more difficult
to locate than others.