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A team of scientists led by researchers from the University of Massachusetts Amherst recently made a startling discovery, using a wind tunnel and a flock of birds. The songbirds, many of which make twice-yearly non-stop flights of more than 1,000 miles to get from the breeding grounds to the wintering grounds, feed by burning lots of fat and a surprising amount of proteins that make up lean body mass, including muscle. , at the beginning of the flight.
This overturns conventional wisdom, which assumed that migratory birds only increased their protein intake at the very end of their journey because they would need to use every ounce of muscle to flap their wings, not fuel. The results were recently published in the Proceedings of the National Academy of Sciences.
“Birds are amazing animals,” says Cory Elowe, the paper’s lead author and a postdoctoral research fellow in biology at UMass Amherst, where he earned his Ph.D. “They are extreme endurance athletes; a bird that weighs half an ounce can fly, nonstop, flapping for 100 hours straight, from Canada to South America. How is it possible? How do they fuel their flight? »
For a very long time, biologists assumed that birds fueled such feats of endurance by burning up fat stores. And indeed, fat is an important part of the secret mix of migratory birds. “The birds in our tests burned fat at a consistent rate throughout their flights,” says Elowe. “But we also found that they burn protein at an extremely high rate very early in their flights, and the rate at which they burn protein decreases as flight duration increases.”
“This is a new idea,” says Alexander Gerson, associate professor of biology at UMass Amherst and lead author of the paper. “No one has been able to measure protein burning to this extent in birds before.”
“We knew birds were burning protein, but not at this rate, and not this early in their flights,” Gerson continues. “Plus, these little songbirds can burn off 20% of their muscle mass and then rebuild it in a matter of days.”
To make this breakthrough, Elowe had the help of bird banding operators at the Long Point Bird Observatory, Ontario, along the north shore of Lake Erie. Every fall, millions of birds congregate near the observatory on their journey to their wintering grounds, including the Black-capped Warbler, a small songbird that travels thousands of miles on its migration. After capturing 20 Blackpolls and 44 Yellow-rumped Warblers – a shorter-range migrant – using mist nets, Elowe and his colleagues then transported the birds to Western University’s Advanced Facility for Avian Research, which has a specialized wind tunnel specially designed for bird watching. in flight.
Elowe measured the fat and lean body mass of the birds before the flight, then, when the sun went down, let the birds free in the wind tunnel. Because birds naturally migrate at night, Elowe and his colleagues would then stay awake — at one time, for 28 hours — watching when a bird decides to rest. At this point, the researchers would retrieve the bird and again measure its fat and lean body mass content, comparing them to the measurements taken before the flight.
“One of the biggest surprises was that each bird still had a lot of fat when they chose to end their flight,” says Elowe. “But their muscles were emaciated. Protein, not fat, appears to be a limiting factor in determining how far birds can fly.
Researchers still don’t know why birds burn up such vast stores of protein so early in their journeys, but the possible answers open up a wide range of avenues for future research.
“How exactly is it possible to burn your muscles and internal organs and then rebuild them as quickly as these birds do,” Gerson wonders. “What information on the evolution of metabolism could these birds provide? »
Elowe is curious about shivering – non-migratory birds that overwinter in cold areas keep themselves warm by shivering. “It’s also a feat of endurance,” says Elowe. “Do birds feed their winter chills the same way? And as the world heats up, which method of coping with the cold – shivering or migrating – might be the best option for surviving? »
Thanks to the University of Massachusetts Amherst for providing this news.
The far-flying black warbler crosses the continent before crossing the ocean
