Athletes aren't the only ones who improve their performance by doping. A new study suggests that migrating birds can also boost their fitness without exercise or effort--simply by eating.
Jean-Michel Weber, a biologist at the University of Ottawa in Canada, first became interested in natural doping when studying the semipalmated sandpiper. Like all migrating birds, the tiny sandpiper instinctively heads to warmer climates for the winter. The 3000-km trek from the birds' summer home in the Canadian Arctic to the South American coast includes 3 days of nonstop flight over open water. The journey is so arduous it can kill younger or weaker members of the flock. But the birds prepare for the effort. The cooling temperatures and shortening days cause hormonal changes that spur their diets to change and their guts to grow larger so they can consume more food. They even begin exercising, flying more frequently to build up their muscles for long and difficult journeys.
The doping comes in when the birds fatten up for their flight. Near the beginning of their journey, sandpipers stop at the Bay of Fundy on Canada's eastern coast to gorge on mud shrimp, 1-cm-long crustaceans loaded with omega-3 fatty acids. Over 2 weeks, the frantic feeding doubles each sandpiper's body mass. But 3 years ago, Weber noticed that the feast had another effect: It makes sandpipers' muscles use oxygen more efficiently, enhancing the birds' endurance. He began to suspect that the food itself--the omega-3 in particular--was somehow boosting the birds' fitness, but he couldn't tease out its effects from the hormonal changes and increased exercise leading up to migration.
To isolate diet's role, Weber and colleagues took exercise and migration out of the equation. They turned to the bobwhite quail, an unrelated sedentary bird that doesn't migrate and seldom flies. For 6 weeks, the scientists fed 40 couch-potato quails a combination of omega-3 fatty acids from fish oil. To the researchers' surprise, the quail's oxidative capacity--their muscles' efficiency at using fuel--shot up 58% to 90%.
"I thought I would find an increase," says Weber, whose team reports its findings today online in The Journal of Experimental Biology, "but I was very surprised to see such a large increase." The quail's transformation outpaces 10 weeks of endurance training for a horse and 7 weeks for a human, all without exercising. Although the study did not measure changes in the quail's actual performance--"teaching a quail to fly in a wind tunnel is probably impossible," says Weber--the rise in oxidative capacity in the birds mirrors the increase observed in sandpipers just before they migrate.
Weber's study is an important first, says Scott McWilliams, a physiological ecologist at the University of Rhode Island, Kingston, who also works on migratory birds. "The past evidence was all correlational," he says, "but this directly shows that by just changing diet, you can double your oxidative enzymes."
So can humans learn anything from these birds? Although omega-3 is known to ward off heart disease and alleviate depression in people, McWilliams cautions human couch potatoes against relying on fish oil to boost their fitness. Human endurance athletes metabolize less fat than do their feathered counterparts, he notes, so they might not enjoy the same natural doping effect. "You should get your omega-3," says McWilliams, "just not for the same reasons birds do."