AbstractTo see if genetic differences correlate with differences in agonistic behavior, 225 encounters within and between color morphs of the white‐throated sparrow (Zonotrichia albicollis) were observed in feeding groups of different sizes and morphic compositions. Tan morphs lack the M chromosome that replaces either of two chromosomes in the white morph. The data were analysed using quantitative models accounting for the proportions of morphs present, and the principal finding was that morphs are equally frequent recipients of aggression but the white morph was the aggressor more frequently than by chance expectation — regardless of the morph of the recipient, the size of the group or the morphic composition of the gr