White-throated sparrows.

Some of the birds have primarily white and black feathers in the median and lateral crown stripes of their heads. Others have primarily tan and brown crown stripes. The two forms are genetically determined. Individuals almost always mate with a bird of the opposite morph. Males of both color types prefer females with white stripes. Both types of females prefer tan-striped males. White-striped males blame their parents for this. White-striped birds are more aggressive than tan-striped ones. White-striped females may out-compete tan-striped females for tan-striped males. Male birds that insist on wearing hats are unlucky in love.