A young bird that goes hungry too often isn't likely to grow up to be an avian Caruso, a new study finds. Later in life, these males warble meager repertoires, potentially compromising chances with the opposite sex.
Female birds often look for extravagant plumage or brightly colored beaks when selecting a mate. That's because these features can hint at a male's overall vigor (ScienceNOW, 3 April ). Females also prefer males with virtuoso singing, but researchers haven't understood how musical ability might reflect health. One possible explanation, the so-called nutritional stress hypothesis, is that males that go hungry at key times early in life, when the brain structures associated with singing are developing, end up with lame songs. Females looking for the best mate, the theory goes, would do well to avoid males who have fallen on such hard times.
To test this idea, Kate Buchanan, a biologist at Cardiff University in Wales, and her colleagues reared 48 male and female European starlings. Half of the birds were fed around the clock as much as they could eat. The other half was fed at irregular intervals for 80 days, beginning approximately 1 month after they hatched. Nine months later, males that experienced nutritional stress spent less time singing and they produced shorter song bouts.
The team also found preliminary evidence that poor nutrition affects other aspects of the animal's fitness. Stressed animals produced fewer antibodies to fight off injected alien blood cells. But another important feature of the immune response was normal, and hormonal levels differed little between the birds, Buchanan reports online this week in the Proceedings of the Royal Society. Although tentative at the moment, the findings nevertheless suggest “that [hunger-stressed] birds are not doing quite that well,” says Buchanan.
The study “helps confirm that there can be lasting consequences of developmental stress [on singing],” says Steve Nowicki, a neurobiologist at Duke University in Durham, North Carolina. A lot of work remains to be done, he adds. How nutritional stress affects brain development and how it is ultimately linked to male fitness is not yet known. But the present findings “open the door to begin to ask what females are getting out of this,” says Nowicki.