A bird's scent may indicate how many offspring it will produce.


Danielle Whittaker of Michigan State University in East Lansing and her colleagues analysed compounds that evaporate from the oily secretions that birds spread over their feathers when preening. The team collected oil from 12 female and 22 male dark-eyed juncos (Junco hyemalis; pictured) and found that the oil's chemical profile differed between the sexes.

Birds that released more chemicals characteristic of their sex produced more offspring. And males with more 'female' odours fledged more hatchlings fathered by other birds from their nests. Overall, the smell of a bird was a better predictor of reproductive success than either size or plumage.

Anim. Behav. http://doi.org/nr3 (2013)