Assortative mating in captive cowbirds is predicted by social experience

Experimental evidence has shown that brown-headed cowbirds, Molothrus ater, display pairing preferences for their native population. Here, the question of whether social experience affects such preferences was tested. Four groups of juvenile female and male cowbirds from a South Dakota population were housed either with adult birds from the same population or with adult birds from an Indiana population. The Indiana population is from a different subspecies from the South Dakota population, and adult Indiana cowbirds display communicative behaviours that are differe nt from adult South Dakota cowbirds; the communicative cultures of the two populations thus are distinct. The pairing and mating patterns of the juvenile females and males were assessed during their first two breeding seasons. In the first year, 71.4% of the pairings that occurred in a testing aviary were between unfamiliar birds of the same cultural background. In the second year of testing, after another winter of social experience with adults of their respective cultures, 86.2% of the pairings, and 77.3% of the copulations, that occurred were between birds of the same cultural background. These data demon­ strate the learning of population-speci fic courtship and mating patterns in cowbirds, and are amon g the strongest experimental data to date indicating assortative mating in birds based upon social experience.