Bird's diet may reflect warming

PROVIDENCE -- A species of songbirds is avoiding insects that have ingested leaves with elevated carbon dioxide levels, a finding that may show how global warming affects the food chain, researchers say.

The researchers at the University of Rhode Island have been studying the eating habits of the black-capped chickadee, a common songbird in New England. In a recent study, they say the birds are not eating insects that have eaten leaves with high carbon dioxide levels.

Carbon dioxide, emitted into the atmosphere primarily by power plants and automobiles, is a major contributor to global warming.

The URI study sought to establish whether 30 chickadees caught around the school's campus in South Kingstown could detect the presence of the compounds tannins and phenolics in 30,000 caterpillars fed leaves from trees that produce the compounds when subjected to high amounts of carbon dioxide.

Lead researcher Scott WcWilliams, associate professor of wildlife physiology, said the idea for the study came after a discussion with University of Wisconsin entomologist Richard Lindroth about his study of the effect of carbon dioxide on gypsy moth caterpillars.

"He was trying to make the case for large effects that compounds have on insects," McWilliams told The Providence Journal.

McWilliams and a student conducted the study using the songbirds, known to be intelligent with good memories, as the subject. After three days, the scientists say the birds avoided caterpillars with high levels of the compounds. High tannin levels, for example, force the birds to eat more and expend more energy to detoxify themselves, the researchers said.

Jeff Price, director of climate change impact studies at the nonprofit American Bird Conservatory, said the study has value, but cautioned that it covers the behavior of only one species of songbird.