Brown-headed cowbirds are robin-sized black birds whose range covers most of North America. From a people's point of view cowbirds are what we might call deadbeat parents. Cowbirds lay their eggs in the nests of other bird species, and the cowbird nestlings are raised by the foster parents.
Since the cowbirds spend their formative months with birds of an entirely different species which has separate habits, songs, etc., "How does a cowbird know it's a cowbird?" A good question, since singing the right songs and making the right moves are essential to establishing territory and attracting mates, it's vital that one do these things right.
One would think that the cowbird's behavior would be "hardwired", that it would just know what it is. But work done by Meredith West and her colleagues has shown that this is not the case.
Before a group of young cowbirds had time to socialize much, West had them stay the winter with a group of canaries. In the spring they were turned loose in an aviary with a mixed group of birds. What happened was weird: the cowbirds sang like canaries, and tried to court canaries. They ignored the other cowbirds! And the canaries ignored their advances.
After the mating seasonwhich these birds were really unsuccessful in, by the waythe cowbirds spent the next winter with a group of their own kind. The following spring they were again turned loose with a mixed group of birds, and this time they behaved like cowbirds. They sang cowbird songs, made cowbird moves, and did those things that would increase the cowbird population.
What this means is that the cowbirds have to learn how to behave like cowbirdsit doesn't just come naturally.