Gender determination and lack of sex-specific West Nile virus mortality in American crows

With a set of external measurements from a sample of known-sex American crows (Corvus brachyrhynchos) in central Illinois, we determined whether a published discriminant function for sex determination was applicable to crows in a different geographic location than the reference sample. Low classification success with this equation, likely due to geographic size differences in crows between regions, led to the creation of new age-specific discriminant functions, which correctly classified the sex of 100%, 100%, and 89% of hatch-year, subadult, and adult crows, respectively. This technique for gender determination is of timely importance as the American crow is a sentinel for West Nile virus transmission, and ecological studies of this species are important in understanding transmission dynamics. Gender determination by discriminant function of these Midwestern crows indicated that the 2002 West Nile virus epizootic did not cause sex-biased mortality.