2023-04-17 19:00:00
It is a well-known fact that migratory birds can fly incredibly long distances effortlessly and spend correspondingly long periods of time in the air without a break. A new study with birds flying in a wind tunnel in the journal PNAS shows that they rely heavily on proteins, especially in the first few hours.
The researchers conclude that how far the birds can travel depends less than previously thought on their fat reserves.
As a rule, science assumes that it is the fat reserves of migratory birds that determine how far the animals make it in one leg of their journeys, which can sometimes be several thousand kilometers, writes the team led by lead author Cory Elowe from the University of Massachusetts (USA), which also included Julia Slezacek from the Konrad Lorenz Institute for Comparative Ethology at the University of Veterinary Medicine, Vienna. It has long been assumed that proteins are also used as a side effect, but it was previously assumed that only a small but continuous proportion came from this “fuel source”.
The team checked whether this makes sense using several specimens of the North American striped warbler (Setophaga striata) and its close relatives, the crowned warbler (Setophaga coronata). To do this, the researchers let the animals fly non-stop in a wind tunnel for up to 28 hours. While the striped warbler, which is up to 15 centimeters long, is a long-distance migrant among birds, the similarly small crowned warbler is more of a short-distance migrant.
After the flights, the scientists checked how representatives of both species react to the exertion of flight in an artificial environment by measuring the fat content and energy consumption of the animals. Three striped warblers completed the entire 28-hour flight – and, according to the researchers, set a new record for a continuous flight in the wind tunnel.
The three marathon fliers then landed with relatively little reduced fat reserves but reduced flight muscles, indicating greater protein breakdown, the paper says. A surprisingly similar picture emerged across both bird species, with fairly continuous fat consumption and “high rates of protein loss” especially at the beginning of the flights, which decreased sharply over time.
According to the team, the mechanisms behind animal long-distance flights should be thought differently in the future. Apparently, not only are the fat reserves the main source of fuel for the birds, but protein breakdown is also likely to be a limiting factor for the duration of the flight.
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