Long perceived as a mere mysterious instinct, the first journey of migratory birds is actually the product of a complex mechanism. It blends an innate genetic heritage, early learning of the environment, and a surprising ability to correct its course mid-flight.
Encoded in the Genetic Code
The cuckoo’s experience perfectly illustrates the innate component of migration. Hatched and raised in the nest of other species, these chicks leave Europe on their own, never having followed their biological parents. Yet they can reach Africa, guided by an inherited migratory program that tells them, among other things, an initial direction.
To study this hereditary transmission, scientists observed two populations of blackcaps, one migrating southwest and the other southeast. The offspring born from crosses between these two groups chose an intermediate southern trajectory. These results show that migratory direction has a genetic component combining the traits of each parent.
Natural Compasses
Although endowed with an innate sense of direction, songbirds must also rely on external cues to stay on course. Among the remarkable abilities of migratory birds is the use of the Earth’s magnetic field. They can also orient themselves by the sun during the day, combined with their internal biological clock. Finally, some use the celestial map to guide their nocturnal movements.
However, reading the stars does not come naturally and requires a prior phase of learning. Experiments conducted on young birds under the dome of a planetarium revealed the importance of observing the night sky before migration. Birds deprived of this learning could not orient themselves correctly using the stars. They need to observe their surroundings during early life to identify the pivot point indicating north.
An Ability to Correct Deviations
The classic model pictured the first journey as a path guided by a programmed direction and duration. Yet some young migrants show a more elaborate navigational capacity. Moved about 1,800 kilometers east, young cuckoos bent their trajectory westward, toward their usual migratory corridor. These observations demonstrate a capacity to adjust before even reaching their destination.
All of these discoveries redefine the first flight of migratory birds as the culmination of progressive preparation. It blends the inherited heading from parents, the learning of celestial cues, and, in some species, the ability to correct deviations. The first migratory journey is thus prepared in the early weeks of life for a young bird.
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