External Sex Characters of Harris' Hawks in Winter
Abstract
From 585 individual Harris' Hawk (Parabuteo unicinctus harrisi) banded in winter in Texas, plus 3 recoveries and 4 found dead, we conclude that, although there are no apparent plumage differences between males and females, there are practicable sex criteria based on body size. Males take a U.S. Fish and Wildlife Service band size 7a, females 7b (discrepancy, 1.8%). Males fit into holding tubes of 106 mm inside diameter, females 128 mm (about 2% discrepancy). Sexing by weight and wing measurement is most accurate when birds are segregated according to age. There was no overlap in weights in the younger age classes and only 0.3% among adults. Wing chord overlapped by 0.5 to 2.0% and flattened wing by 0 to 1.3%, depending upon age. By combining several criteria, one can be virtually certain about sex diagnosis.
Nineteen P. u. harrisi from Tamaulipas agreed with the Texas material; 32 P. u. superior from Sonora showed no overlap in weight or in either wing measurement.
Ten birds from Texas, one from Tamaulipas, and two from Sonora showed possible anomalies in molt or pattern of the outer two primaries that confused aging. There was also a suggestion that fully adult primaries might not be attained until the second year.
