PrincetonUniversity
 

For migrating birds, seeking rest is more tiring than flying

by Steven Schultz
Highway travelers know the relief of finding a great place to stay after a long night on the road. Migrating birds are no different.

A study led by a Princeton researcher has shown that birds expend more energy seeking food and shelter between the legs of their journey than they do flying. "Flight itself is costly, but foraging and preparing for the flight is even more costly," said Martin Wikelski, a biologist and lead author of a study that involved tracking birds for hundreds of miles as they traversed the American Midwest.

One implication of the finding, published in the June 12 issue of Nature, is that urban and suburban homeowners play a critical role in preserving migratory routes. The birds followed in the study often stopped in the backyards of populated areas to look for food and prepare for the next flight.

"You really have to keep your garden in good shape so the birds can come through and make it up to Canada," Wikelski said. Migrating birds need bushes and some natural undergrowth, not just lawn and flower gardens, he said.

The researchers conducted the study by trapping migrating thrushes in Urbana, Ill., and injecting them with water that contained harmless heavy isotopes of hydrogen and oxygen. Working with one bird at a time, they attached a small radio transmitter between its wings and released it. They then drove through the night tracking the bird until it landed at dawn, covering an average of 170 miles over 4.6 hours.

In addition to the specific findings, said Wikelski, the study demonstrates the potential for rigorous, quantitative field research on birds. Previous research focused on studying bird migration in the lab or looking at general patterns of weather and migration, but did not track individual songbirds in the field. Although radio tracking is challenging, it offers a chance to pull together various areas of research in a real-life situation, he said.

Wikelski and colleagues are now conducting further studies in which they continuously monitor the heart rates of birds during migration and look more closely at the effects of weather and atmospheric dynamics.

The full story is available in a news release.

Princeton biologist Martin Wikelski led a team of researchers in studying how birds expend energy during migration. The researchers attached radio trasmitters to the birds and tracked their progress while driving hundreds of miles overnight to keep up.

photo: Ruth Stevens