Assortative mating in lesser snow geese (Anser caerulescens).

Assortative mating occurs in the dimorphic lesser snow geese in the wild. Mixed matings between the blue and white phases are much less frequent than would be expected by chance. Evidence from marked birds in field conditions indicated that mate choice was correlated with familial color. Birds from white families usually chose white mates, birds from blue families usually chose blue mates, and birds from mixed families chose mates of either color. Similar results were obtained under captive conditions when offspring from foster families with particular parental and offspring color combinations were allowed to choose mates. Both parental color and sibling color appeared to influence mate choice. The bird's own color did not appear to be important in mate choice in either field or experimental conditions, and in those cases where male and female parents differed in color neither parental color was more influential than the other in determining offspring mate choice. The results provide the first evidence, to our knowledge, that mate selection based on familial appearance operates intraspecifically in the wild.