Early Bird Gets the Worm, Then Saves it for Later, Study Finds

Several avian species are giving new meaning to the "early bird gets the worm" adage, after researchers documented them hunting for food early in the day but holding off on eating until afternoon to reduce chances of starvation overnight.

Ornithologists from Oxford University report that the birds -- which include great tits (Parus major), blue tits (Cyanistes caeruleus), marsh tits (Poecile palustris), coal tits (Periparus ater), and nuthatches (Sitta europaea) --- scout for food in the mornings, but only return to eat it in late afternoon to maximize their chances of evading predators. The late afternoon meal also ensures the birds will have enough nutrition and energy to survive the night.

"Birds have to store body-fat to avoid starving during the cold winter nights, but this can make them slower and less maneuverable so that they are more likely to be caught by predators," said Damien Farine of Oxford University's Department of Zoology, who led the research. "So there is a trade-off, where birds need to remain lean enough in order to 'outrun' their predators, or at least the next slowest bird, during the day but also store enough fat to survive each night."

Previous research had concluded that when faced with a predation risk, birds delay putting on fat until late in the day. For this study, the researchers were interested to see what the birds were up to in the hours between securing food and eating.

"We used new tracking technologies to investigate how great tits, blue tits, and other common garden birds, balance the competing risks of predation and starvation," said Farine. "Our results show that these birds display very different patterns of food discovery in the morning and afternoon; very few new food sources were found during the afternoon, whereas nearly every new food source that we put out during the morning was quickly discovered. It supports the idea of an 'early bird' strategy of scouting for food early on so that they can return to feast a couple of hours before dusk in preparation for a long winter's night."

Winter is a particularly tough time for small garden birds. There are fewer natural food sources around, and predator birds, such as the sparrowhawk, are actively hunting to secure their own fat stores. Small birds can lose up to 10 percent of their body weight overnight in winter, so failing to secure an adequate amount of food can spell the end for small birds.

"Because small birds can't reproduce without surviving the winter they have evolved a complex set of behaviors that enables them to maximize their chance of both surviving predators and avoiding starvation," Farine said. "It's a good example of how animals alter their behavior to respond to constantly changing environmental conditions. It also shows how new technologies, like tiny PIT tags, are enabling us to explore questions about animal survival strategies at an unprecedented scale."

PIT tags are the tiny radio transmitters that the researchers fitted to more than 2,000 birds in Wytham Woods near Oxford. To collect feeding data the researchers set up 101 feeders, which they moved to different locations throughout the woods each day. The PIT tags enabled the researchers to track the birds' movement across different feeding locations throughout the forest. 

The research is published in the Royal Society journal Biology Letters.