Singing behavior, mating associations and reproductive success in a population of hybridizing Lazuli and Indigo Buntings

Populations of Lazuli Buntings (Passerina amoena) and Indigo Buntings (P. cyanea) overlap in their distribution and hybridize in the Great Plains of North America. We conducted a 4-year field study of color-banded Indigo, Lazuli, and hybrid Buntings to address questions about mating behavior, male song and plumage traits, and reproductive success. From previous studies, we knew that males of these two taxa can learn one another's song traits and that song is important in eliciting sexual behavior in females. Here, we explore the possible role of intersexual vocal communication in explaining hybrid matings. We classified males and females as lazuli, indigo, or hybrid on the basis of plumage, and recorded male songs and described their acoustic features. We tested for associations between song traits and plumage phenotypes of the males, and between plumage phenotypes of females and the plumage and song traits of their mates. We found positive assortative mating between male and female plumage types, and between male song phrases and female plumage. Data on reproductive success of the different mating associations suggest lower fitness of pairings involving hybrids, especially those in which the female was hybrid. We conclude that there is selection against hybrids, but that between-species crosses are relatively common because, at least to some degree, females use learned song traits of males in mate choice.