Feigning Health For A Bit Of Romance?
Most people can relate to the adage "beauty is pain," having suffered through a taxing diet or a grueling gym workout. But the male northwestern song sparrow takes things a step further.
According to a new study, he's willing to risk a prolonged illness just to look good for the ladies.
Noah Owen-Ashley, a wildlife biologist with the Alaska Department of Wildlife Management in Barrow, hit upon the theory while trying to learn more about how birds behave when they're sick. Scientists have made birds feel ill in the lab by injecting them with bacterial lipopolysaccharide (LPS) - a compound that induces "sickness behaviors" such as reduced appetite and less frequent interaction with other birds. Owen-Ashley was curious whether birds in the wild would respond in the same way.
Using nets and a caged bird decoy with prerecorded bird song, Owen-Ashley and his team captured 30 male song sparrows in western Washington State in the spring and fall of 2001. The team injected half of the birds with LPS and the other half with saline. The researchers then let the birds go and recaptured them 24 hours later (leg bands indicated which birds had received which injection).
In the winter, LPS had a clear impact. Birds injected with the compound lost 5% of their body weight, while those injected with saline maintained a healthy appetite. LPS also made the birds less aggressive than the controls.
But LPS had much less of an effect in the spring, causing just a 1% loss of weight. And the birds injected with LPS sang just as many territorial songs and made as many aggressive darts at the decoy as those that had received saline, the team reports in the current issue of the Journal of Experimental Biology. So there seems to be something about the springtime - the urge to breed, presumably - that made birds ignore the LPS, says Owen-Ashley.
One factor could be hormones. High levels of corticosterone or testosterone - shown to rise in the springtime - likely suppress the immune response that makes birds feel ill. Alternatively, the fat stores of wintering birds may make them less worried about shedding a few pounds. Or it may be that wild birds simply ignore their symptoms during the breeding season. Despite a poor appetite, males may try to maintain their weight so as not to appear malnourished to a female's critical eye, says Owen-Ashley.
"I think that it was a heroic study," says Randy Nelson, a behavioral biologist at Ohio State University in Columbus. "This is hard stuff to do." Next, he says, it would be interesting to see if breeding success correlates with the suppression of the sickness response.
"Even birds made to feel sick in the spring exhibit territorial behaviors, such as aggression towards this caged decoy. Credit: John C. Wingfield"
Source: Science Daily
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