New science research shows that birds kick off their non-stop intercontinental migration flights with a protein boost
A team of scientists led by researchers at the University of Massachusetts Amherst has recently made a surprising discovery, with the help of a wind tunnel and a flock of birds.
Songbirds, many of which make twice-yearly, non-stop flights of more than 1,000 miles to get from breeding range to wintering range, fuel themselves by burning lots of fat and a surprising amount of the protein making up lean body mass, including muscle, early in the flight.
This flips the conventional wisdom on its head, which had assumed that migrators only ramped up protein consumption at the very end of their journeys, because they would need to use every ounce of muscle for wing-flapping, not fuel.
Cory Elowe, the paper’s lead author and a postdoctoral researcher in biology at UMass Amherst, where he received his PhD, said: “Birds are amazing animals.
“They are extreme endurance athletes; a bird that weighs half an ounce can fly, non-stop, flapping for 100 hours at a time, from Canada to South America. How is this possible? How do they fuel their flight?”
For a very long time, biologists assumed that they fuelled such feats of endurance by burning fat reserves. And indeed, fat is an important part of a migrator’s secret mix.
Elowe said: “The birds in our tests burned fat at a consistent rate throughout their flights. But we also found that they burn protein at an extremely high rate very early in their flights, and that the rate at which they burn protein tapers off as the duration of the flight increases.”
Alexander Gerson, associate professor of biology at UMass Amherst and the paper’s senior author, added: “This is a new insight. No one has been able to measure protein burn to this extent in birds before.
“We knew that birds burned protein, but not at this rate, and not so early in their flights.”
“What’s more, these small songbirds can burn 20% of their muscle mass and then build it all back in a matter of days.”
Migrate at night
To make this breakthrough, Elowe had help from the banding operators at Long Point Bird Observatory, in Ontario, along the northern shore of Lake Erie.
Every autumn millions of birds gather near the observatory on their journey to their wintering grounds – including the blackpoll warbler, a small songbird that travels thousands of miles during its migration.
After capturing 20 blackpolls and 44 yellow-rumped warblers – a shorter distance migrant – using mist nets, Elowe and his colleagues then transported the birds to the Advanced Facility for Avian Research at Western University, which has a specialised wind tunnel built specifically for observing birds in flight.
Elowe measured the birds’ fat and lean body mass pre-flight, then, when the sun set, let the birds free in the wind tunnel.
Because the birds naturally migrate at night, Elowe and his colleagues would then stay awake – at one point for 28 hours – watching for when a bird would decide to rest.
At that point, the researchers would collect the bird and again measure its fat and lean body mass content, comparing them with the pre-flight measurements.
Elowe said: “One of the biggest surprises was that every bird still had plenty of fat left when it chose to end its flight, but their muscles were emaciated.
“Protein, not fat, seems to be a limiting factor in determining how far birds can fly.”
The researchers still don’t quite know why the birds are burning such vast stores of protein so early in their journeys, but the possible answers open up a wide range of future research avenues.
Garson said: “How exactly is it possible to burn up your muscles and internal organs, and then rebuild them as quickly as these birds do?”
“What insights into the evolution of metabolism might these birds yield?”
Shivering or migrating
Elowe is curious about shivering – non-migratory birds that overwinter in cold areas keep themselves warm by shivering.
He said: “This is also a feat of endurance. Do birds fuel their winter shivering spells the same way?
“And as the world warms, which method of coping with the cold – shivering or migrating – might be the better option for survival?”
The results appeared recently in the Proceedings of the National Academy of Sciences.
Image1 : The blackpoll warbler can fly for thousands of miles without taking a break. © Sherri and Brock Fenton (Western University, London, Ontario).
Image 2: A yellow-rumped warbler. © Rhododendrites (CC BY-SA 4.0) https://creativecommons.org/licenses/by-sa/4.0/legalcode
