Navigation map has to be learned by migration-naïve Eurasian reed warblers

It used to be thought that young migrating birds perform their first migration using an innate 'clock-and-compass' programme that specifies the timing of onset of movement and its direction and duration, but did not require information about the bird's current position¹. In classic displacement experiments, young birds continued to fly in their normal migratory direction, whereas adults were able to adjust their course after displacement². More recent evidence, however, suggests that young birds may estimate their position and adjust their behaviour when delayed or displaced, even during their maiden flight^3,4. Evidence for innate magnetic map responses in hatchling sea turtles and juvenile salmonids⁵ suggests that birds may also inherit magnetic positional information. We have investigated this hypothesis in the Eurasian reed warbler (Acrocephalus scirpaceus), a species in which compensation for physical and virtual magnetic displacement has been demonstrated in experienced migrants^6,7. We used migration-naïve birds trapped in early autumn as juveniles and kept in captivity over winter. In spring, the birds were tested first in the natural magnetic field at Rybachy in Russia, and then under a virtual magnetic displacement to Keele, UK. Under the virtual magnetic displacement, the birds did not change their orientation as expected if they possessed a magnetic map. We found no evidence that migration-naïve Eurasian reed warblers use a functional innate magnetic map under the conditions of our experiment. In this species, the first migration is guided primarily by an inherited compass programme, whereas a functional magnetic map develops through migratory experience.