Better-Smelling Birds Produce More Offspring

A dark-eyed junco. Photo courtesy of Nicole Gerlach / MSU

With birds’ flashy feathers and melodic songs, we have long considered sight and sound to be important factors in avian females choosing a mate. Smell, on the other hand, has been all but ignored. But a new study suggests that odors may also be important when it comes to mating.

Danielle Whittaker, at the BEACON Center for the Study of Evolution in Action at Michigan State University, has been studying compounds in “preen oil.” Birds secrete the stuff from a gland near their tails and then use their beaks to spread it over their feathers. While preen oil is known to protect feathers from water, heat, and the sun, Whittaker says it also contains odor-causing chemicals in sex-specific ratios. That means males have more of certain chemicals, while in females, other chemicals predominate.

 “These odors are there primarily in the breeding season,” says Whittaker. “That seasonal difference really suggests to me that they would be important to reproductive behavior.”

Baby juncos. Photo courtesy of Nicole Gerlach / MSU

Though Whittaker and others have suspected for a while that these odor cues existed, “this is the first time anyone has connected it to reproductive success.”

Whittaker’s team studied dark-eyed juncos.  They found that males whose chemical profile more closely matched the typically “male-like” chemical ratio had more offspring; ditto for the females with the “female-like” ratio.

Whittaker says that the exact role of the compounds is still unclear. She and her colleagues suspect that rather than mere attractants, the chemicals indicate the quality of potential mates. “We still need a study showing how it’s actually employed in mate choice,” she says. Still, “this is a pretty good starting point.” Passing the sniff test, it seems, may be the key to scoring.


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