Some birds prefer mates with good voices rather than looks

Looks can be deceiving when it comes to finding the right mate. But certain bird species have figured out that a voice can help them make the right decision, say researchers.

A study, conducted by Andrew DeWoody, a Purdue University associate professor of forestry and natural resources, revealed that the higher the pitch of a male bird's song, the more genetic diversity that bird has, making him a better mate for breeding.

"If you have a diverse set of genes, that can translate into physiology and morphology diversity as well. Animals that are heterozygous, or have genetic diversity, are often bigger, stronger or can run faster," DeWoody said.

DeWoody along with former Purdue graduate student Johel Chaves-Campos studied ocellated antbirds in the tropical forests of Central America.

The antbirds survive by tracking army ants, which hunt in large swarms and are capable of killing just about anything in their paths. The birds flit ahead of the swarms and collect arthropods that flee for their lives.

"They wait at the front for the ants to flush out a grasshopper, for example," DeWoody said.

The antbirds have several calls, some to let fellow antbirds know where the army ants are heading, others to attract mates and still others that are defensive or aggressive to protect turf.

The new study involved recording those calls and matching them to DNA samples of the birds. The results suggest that genetic diversity in antbirds affects their physical abilities to produce certain sounds.

"Our results are consistent with the idea that some sound frequencies are biomechanically difficult to produce. Males that are genetically diverse, and therefore expected to be in better physical condition, are able to produce sound frequencies that males with less genetic variation are unable to reach," Chaves-Campos said.

DeWoody said females can pick up on the pitch of the males' songs to decide which birds will make the best mates.

"Females may prefer to mate with males that hit the highest notes because their offspring will have more genetic diversity. Male calls could be honest indicators of their genetic diversity," DeWoody said.

The study was published in the early online edition of PLoS Biology.