Aggressive Performance as a Behavioral Correlate of Plumage Polymorphism in the White-Throated Sparrow (Zonotrichia Albicollis)

Morph and sex-specific differences in aggressive performance were examined in the white-throated sparrow. Among the four morph/sex classes, white-striped males had the strongest response to white-striped models and were the most likely to approach and attend song playbacks independently. The slightly weaker responses of tan-striped males and white-striped females were similar to each other. Tan-striped females were the least aggressive. Aggression by white-striped females enabled tan-striped male x white-striped female pairs to perform as well, or better, than white-striped male x tan-striped female pairs. Tan-striped males paired earlier than white-striped males. An increased prevalence of territorial tan-striped males corresponded to the arrival of females on the breeding grounds. The data are consistent with the hypothesis that negative assortative mating benefits tan-striped males through the supplemental aggression of white-striped females. However, the apparent preference of white-striped females for tan-striped males suggests that there are benefits to negative asortative mating other than those that might arise from differences in aggressive performance.