How migratory birds find their way to their wintering grounds and back to their breeding sites has long been one of biology’s great mysteries. In a new study published in Science, researchers tracked pied flycatchers from eight populations, ranging from England in the west to Tomsk in Siberia in the east.
The results show that the birds winter in various parts of sub-Saharan Africa. What is remarkable is that almost all of the birds first fly via Gibraltar and then along the coast of West Africa before spreading out across the African continent. For birds from Tomsk, which winter furthest to the east in Africa, this means a journey of about 12,700 kilometers – more than 4,500 kilometers farther than the shortest route to their wintering grounds.
“The most surprising finding is that these small birds still follow migration patterns that appear to be inherited from their evolutionary history. Even though there are significantly shorter routes, they continue to take long detours,” says Jan-Åke Nilsson, a biology researcher at Lund University who worked on the study.
The researchers believe the explanation lies in the species’ history. During the last ice age, the pied flycatcher was confined to the Iberian Peninsula. When the species later spread across Europe and further east to Siberia, its genetically programmed migration routes remained.
“Even a bird hatched in Siberia appears to be initially programmed to fly toward Spain and then southward along the west coast of Africa before continuing on to its wintering grounds,” says Jan-Åke Nilsson.
But the study also shows that genes do not control everything. When the birds return to their breeding grounds in the spring, they choose significantly more direct routes. This suggests that the coordinates of the place where they were born are not genetically programmed but are learned early in life.
“The fall migration and the choice of wintering grounds appear to be inherited traits. The spring migration, on the other hand, is based on learning. This means that both genetics and the environment influence migration, but at different times of the year,” says Jan-Åke Nilsson.
This discovery may be significant for understanding how migratory birds are affected by climate change. Since returning to breeding grounds appears to be a learned behavior, birds that establish themselves farther north, to escape very hot weather, may return there in future years as well.
“Our findings suggest that migratory birds amay be better able to adapt their breeding ranges to a warmer climate than previously thought. If birds establish themselves farther north, there is strong evidence to suggest that they will also return there during future breeding seasons,” says Jan-Åke Nilsson.