Assortative mating has been described in the dimorphic Lesser Snow Goose. Evidence is provided which shows that most birds select a mate of a colour similar to that of the family in which they were raised. The pre-pairing experience influences mate choice and thus influences the genetic structure of the population. These results provide the first evidence to our knowledge that mate selection based on familial appearance operates intraspecifically in the wild.
It was found that approximately 10 % of the birds choose mates opposite to the familial colour. These exceptions account for the frequency of mixed matings in the population. Several theories to explain the exceptions are considered.