Vocalizations of Cooper's Hawks during the Pre-Incubation Stage

Abstract

From 1986 to 1990 we studied the vocalizations of 10 mated pairs of Cooper's Hawks (Accipiter cooperii) during the pre-incubation stage. We heard four different vocalizations during nest-building, copulatory, and other pre-laying activities. There was a marked asymmetry in vocalizations between the sexes during the pre-incubation period. Compared to males, female Cooper's Hawks (1) had a larger repertoire of calls, (2) called more frequently, and (3) called during a wider array of activities. We suggest that the various calls signal presence, identity, location, dominance, and non-aggressive motivation. We attribute some of the intersexual differences in pre-incubation vocalizations to the pronounced degree of reversed sexual size dimorphism in this species.