Researchers once thought that when birds paused on long migratory routes, they stopped to build up their fat stores for the rest of their journey.
New research, however, suggests another reason: they refresh their immune system.
In a study published in Biology Letters, researchers found that migrating birds boost their immune systems during breaks from marathon flights. In the fall of 2021, they studied the common redstart, chaffinch and bird’s nest on Heligoland, an island off the German coast along the North Sea that is a popular stopover for birds on the move. every fall.
The researchers captured, tagged and released birds on the island several times a day during the study. They ended up drawing blood from 96 birds twice each during layovers, which ranged from an hour in some cases to just over two weeks.
Blood analysis revealed that during the birds’ breaks on the island, their immune system’s ability to attack bacteria and break down pathogens and potentially harmful cells in the blood increased.
The researchers say the gains were unrelated to the birds’ fat levels. Rather, they think the immune boosts were due to a much-needed break from the strains of the marathon migrations.
Migrations are “really extreme physical activity,” they write, and aside from the physical exertion required, the birds’ journeys take them to new habitats and expose them to a variety of pathogens.
In a press release, the researchers compare layovers to pit stops at gas stations — rest stops that refuel cars and refresh their drivers.
“If you see a little bird in your garden or in the park in the fall and you know it’s heading for southern Europe or Africa, it’s fascinating to wonder why it’s pausing,” Arne Hegemann, a biologist at Lund University in Sweden and co-author of the study, said in the statement. “If they don’t feed or rest, their immune system can’t recover – that’s when they’re at risk of getting sick.”
