A team of American scientists recently made a surprising discovery about the remarkable way migratory birds harness energy to endure transcontinental flights. With the help of a wind tunnel and a flock of birds, the team, led by researchers from the University of Massachusetts Amherst, found that migratory birds burn vast amounts of protein early in their journeys. This overturns the traditional theory, which assumed that migratory birds increase protein consumption toward the end of their flights.
The researchers also discovered that many of these birds undertake non-stop flights exceeding 1,000 miles twice a year to transition from breeding to wintering grounds, fueling themselves by burning fat at a steady rate during their journeys. They can burn up to twenty percent of their muscle mass and completely rebuild it within days.
Cory Eloy, the lead author of the paper and a postdoctoral researcher in biology at the University of Massachusetts Amherst, stated, "Birds are amazing animals. They are incredibly endurance athletes; a half-ounce bird can fly non-stop for 100 hours at a time, from Canada to South America. How is this possible? How do they fuel their journeys?"
He pointed out that "for a long time, biologists assumed that birds fuel such heroic feats by burning fat reserves. Indeed, fats are an important part of the secret mix of migratory birds. Our tests showed that birds burned fat at a steady rate throughout their flights. However, we also found they burn protein at a very high rate very early in their journeys, and the rate at which they burn protein diminishes as the trip lengthens."
Alexander Gerson, an associate professor of biology at the University of Massachusetts Amherst and a senior author of the research paper, explained, "This is a new insight. No one has been able to measure protein burning to this extent in birds before. We knew birds burned protein, but not at this rate, and not so early in their journeys. Moreover, these small songbirds can burn twenty percent of their muscle mass and then completely rebuild it within days."
To achieve this breakthrough, Eloy received help from bird banders at the Long Point Bird Observatory in Ontario, along the northern shore of Lake Erie. Each fall, millions of birds gather near the observatory on their journey to wintering areas, including the blackpoll warbler, a small songbird that travels thousands of miles during migration.
After capturing 20 blackpoll warblers and 44 yellow-rumped warblers—a type of songbird that migrates shorter distances—using mist nets, Eloy and his colleagues transported the birds to the advanced bird research facility at Western University, which features a specialized wind tunnel designed for observing birds in flight.
Eloy measured fat and lean body mass before the journey, then, at sunset—since the birds migrate at night—he released them into the wind tunnel. The scientists monitored the birds to determine when they chose to rest. At that point, the team collected the birds and measured their fat and lean body mass again, comparing the new data to pre-flight measurements.
Eloy remarked, "One of the biggest surprises was that each bird still had plenty of fat left when it chose to end its journey. But their muscles were lean. It seems that protein, not fats, is the limiting factor in determining how far birds can fly."
Scientists still do not fully understand why birds burn such a massive store of protein so early in their journeys, but potential answers open up a wide range of future research avenues.
