Songbirds such as the great reed bird breed in Europe and winter in sub-Saharan Africa. It is amazing in itself that a bird about 30 grams lighter than a golf ball makes a trip of more than 7,000 kilometers twice a year. Swedish scientists have discovered that animals also climb to unexpected heights.
The researchers outfitted 63 large reed birds with data loggers that record when, where and how high the birds were. This is possible thanks to more compact technology with increasingly smaller species. They managed to recover data from fourteen birds.
As expected, the Reed Warblers mainly flew at night and rested during the day. When they had to cross the Mediterranean or the desert, they marched bravely at dawn. One bird continued to fly for up to 34 hours continuously. Instead of staying at an altitude of about 2000 meters, the birds climbed more than 5 kilometers and sometimes more than 6 kilometers. “We didn’t expect this,” explains author Sissel Sjöberg (Lund University). It’s been noted in the past, but was supposed to be an exception. Our research shows that birds do this systematically when they fly during the day. So there must be a reason for that.
It is not clear what this reason is. Birds may try to avoid the clutches of raptors or climb higher to see more. A possible explanation is that the animals are moving to higher altitudes to avoid overheating. The birds themselves produce a lot of heat during flight. When there is additional exposure to the sun during the day, they may need to look for cooler places.