Researchers captured, tagged and released birds on the island several times a day during the study. They ended up sampling the blood of 96 birds two times each over the stopovers, which ranged from an hour in some cases to a little over two weeks.

Blood analysis revealed that during the birds’ breaks on the island, their immune systems’ ability to attack bacteria and disintegrate pathogens and potential harmful cells in the bloodstream increased.

Researchers say the gains weren’t connected to the birds’ fat levels. Rather, they believe the immune boosts were due to a much-needed break from the strains of marathon migrations.

Migrations are “truly extreme physical activity,” they write, and aside from the physical exertion required, birds’ travels take them into new habitats and expose them to a variety of pathogens.

In a news release, the researchers compare the stopovers to pit stops at service stations — rests that refuel cars and refresh their drivers.

“If you see a little bird in your garden or in the park during the autumn and you know that it is heading to southern Europe or Africa, it is fascinating to think about why it is taking a break,” Arne Hegemann, a biologist at Lund University in Sweden and a co-author of the study, said in the release. “If they do not get food or rest, their immune systems cannot recover — which is when they risk becoming ill.”