Social rank, mating and egg fertilization in willow ptarmigan (Lagopus lagopus lagopus).

When captive ptarmigan were allowed to choose their mates freely, the social rank of the male and female correlated significantly. When mates were allocated by the experimenter, without regard to similarity in social rank, fertility was low. When birds of similar social rank were paired, the fertility was high. It is suggested that fertility in captive ptarmigan may be increased if the relative social rank of mating birds is considered.