ITHACA, N.Y. -- While ornithologists consider cowbirds the parasites of the bird world -- commandeering the nests of other birds, hoarding their food and causing starvation -- Cornell University behavioral researchers know these songbirds have a redeeming quality: They carry an important, evolutionary tune.
Like the Mick Jaggers of music, male cowbirds attract females by strutting their masculine feather colors or by their singing ability. But the Cornell scientists have found that both songs and mating rituals correlate with the size of the cowbird brain.
"The female cowbirds are looking only for your genes, so that if you're a male cowbird, you had better look darn good," says Mark E. Hauber, a Cornell doctoral student in neurobiology and behavior. "You had better advertise yourself."
Before this latest research, data that showed a connection between an animal's brain size and mating behavior relied mostly on guesswork, says Timothy J. DeVoogd, Cornell associate professor of psychology. "This is the first time this information has been correlated in a parasitic bird species. No one has ever done this before. Surprisingly there is a close correlation between brain size and a cowbird's abilities and behavior."
The research, "Sexual Dimorphism and Species Differences in HVC Volumes of Cowbirds," appeared in Behavioral Neuroscience, a journal of the American Psychological Association (Vol. 113, Number 5.)
Cowbirds, which are found in North, Central and South America, are medium-sized black birds, that, in some cases, such as shiny cowbirds, also have brown feathers. The birds' songs sweep a large range of frequencies, sounding "like a gargoyle, very bubbly, not very melodious -- like water dripping from a faucet," says Hauber.
The researchers note that the cowbird appears to have brought Darwinian theory clearly into focus. "We think that visual and sexual selection factors seem to go hand-in-hand," says