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Migratory birds take breaks to boost their immune system

Scientists have long known that, after a period of intense physical exertion, vertebrates (including humans) need a period of recovery to lower their heart rates and allow the organism to repair injured muscles. However, more recent studies have shown that intensive physical activity can also affect immune defenses, and that rest is crucial for boosting the immune system too. Now, a team of researchers led by Lund University in Sweden has found that this is also true in the case of migratory birds.

When they migrate, birds regularly stop in one place for a few days to eat and rest – a behavior previously thought necessary to build up new fat reserves which provide fuel for the rest of the migration process. However, scientists have now shown that, during such “pitstops,” they also boost their immune systems.

“This is the first time that this has been demonstrated in wild migratory birds. Our study shows that migratory birds’ stops serve other purposes, besides just ‘refueling.’ They also need other physiological systems to recover. You could compare it to pulling off the motorway into a service station. That is not just for the purpose of refueling, you might also need to recover,” said study senior author Arne Hegemann, a biologist at Lund.

Together with his team, Hegemann examined a variety of small migratory birds such as chaffinches, dunnocks, and common redstarts to assess how their immune systems change when they take breaks during migration. By collecting and comparing data from different individuals and species, they discovered that free-flying migratory birds usually restore several parameters of immune function during their stopovers.

“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. If they do not get food or rest, their immune systems cannot recover – which is when they risk becoming ill. This provides an important part of the puzzle of how migratory birds cope with the physiological challenges they are faced with on their long journeys,” Hegemann concluded.

The study is published in the journal Biology Letters.

By Andrei Ionescu, Staff Writer

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