They say that the early bird catches the worm. The truth, of course, is a bit more complicated.
Garden songbirds have one task during the winter, which is to survive long enough to breed during the spring and summer. Small birds can lose up to 10 percent of their body weight in a single night, so they need to eat well every day. But if they pack on too much weight, they might slow down, leaving them vulnerable to predators such as the sparrow hawk.
Researchers at the University of Oxford attached microchips to more than 2,000 songbirds to track the birds' movements. By outfitting an array of feeding stations with microchip detectors and moving some of the feeders every day, the researchers were able to infer how the birds found their meals.
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Every morning the birds leave their nests and scout, assessing the quality and location of each food source without actually dining.* By fasting in the morning, they remain nimble enough to dodge predators during the daylight hours. As the afternoon wears on, armed with knowledge about where to find food, the birds return to eat, the researchers recently reported in Biology Letters.
The new experiment represents one of the first attempts to investigate how wild songbirds negotiate the competing challenges of feeding enough without becoming a tasty morsel themselves. “Almost all previous studies are either theoretical models or work done in captivity,” says Damien Farine, who led the experiment when he was a graduate student at Oxford.
Similar microchipping schemes will allow researchers to explore further questions about disease transmission among birds, as well as their social networks and cognitive abilities, says Ron Ydenberg, director of the Center for Wildlife Ecology at Simon Fraser University in British Columbia. “These kinds of analyses seemed impossibly complex when I was a graduate student 30 years ago,” he adds.
*Clarification (4/4/14): This sentence should have referred to songbirds leaving their roosts, rather than nests, to scout for food during winter. Songbirds stay in nests only when they raise their young.