When migrating birds make their long flights in spring and fall, they must make regular stops to eat and sleep. When these birds are exhausted, they sleep in a more vulnerable way than when they are in better condition. Italian, German, Austrian and Swedish researchers describe this finding in the journal Cell Press .

Twice a year (among other things) small songbirds fly from their wintering places in Africa to their breeding grounds in Europe and vice versa. Up to 80 percent of these migration periods can consist of rest periods where the birds eat and sleep.

While the birds rest, they usually remain partly alert and stick their heads straight ahead. They are vulnerable to predators during sleep.

The birds made themselves even more vulnerable when they were really exhausted, the scientists discovered. Then they put their heads under the wings, so that they cannot watch out for possible danger.

On the other hand, the birds better retain the heat when they plug in and slow down their breathing and metabolism, reducing their energy consumption.

Garden whistlers make a stopover on an Italian island

The researchers observed the songbird gardeners, or the Sylvia borin , during their stops on the Italian island of Ponza, west of Naples. During their breeding periods, garden whistlers live in countries such as the Netherlands and Belgium.

Scientists believe that little is known about the behavior of migratory birds, except about how they navigate and which routes they take. Insight into the sleeping behavior of these birds provides more insight into how the flights are organized and what the interests of the stopovers are.