AGE AND SEX DIFFERENCES IN THE SIZE OF PREY OF THE SHARP-SHINNED HAWK

Abstract

We trapped Sharp-shinned Hawks (Accipiter striatus) during fall migration, using House Sparrows (Passer domesticus), European Starlings (Sturnus vulgaris), and Ringed Turtle Doves (Streptopelia risoria) as lures. Adults and males initiated attacks on sparrows more frequently than juveniles and females. Adult females initiated attacks on starlings and doves more often than adult males, but there was no such difference between the sexes in juveniles. Females actually struck all three species of lure more frequently than males, and juvenile females struck lures more frequently than adult females. There was no age difference in the incidence of strikes by males. Larger (longer-winged) juvenile males and females attacked starlings more often than smaller juveniles, but there were no size differences in strikes on prey in any age and sex group of hawks, suggesting that sexual dimorphism in size is not a result of selection for differences in prey size. Females struck disproportionately larger lures than males, presumably because they are less efficient at capturing smaller prey. Juveniles attacked doves as frequently as starlings, and there was little age difference in the incidence of strikes, suggesting that inexperience in judging the size of prey is an inadequate explanation for the many attacks that fail to result in strikes.