targets? After all, every bird flies on its own and then mostly at night. Moreover, the older birds generally leave the breeding grounds before the young birds. This means that the young birds probably cannot benefit from the experience of the veterans nor orientate themselves with the help of conspicuous features of the countryside.
Instead, they presumably follow an inborn flight program which specifies the direction and the distance for them. However, such a built-in navigation system alone is not sufficient, as calculations on the computer show. The researchers simulated on a computer how the flight routes would look if the birds followed a compass-clock navigation system exclusively, or if they additionally orientated themselves via topographical features. “In the simulations, even with shorter stretches, the stopovers were further apart than those observed in nature. Even when the simulations took into account that deviations from the correct flight route end fatally for young birds at particular barriers such as mountains or large bodies of water, the calculated flight corridors were still broader”, explains Wikelski.
A pure compass-clock navigation system cannot therefore explain the narrow flight corridors of the cuckoos. “Cuckoos apparently take into account additional information from their environment such as winds, odours or structures in the landscape. They do not just follow such indications, but always know beyond this exactly where they are and head directly for intermediate targets - perhaps with the help of the odour of the landscape, which they know from earlier journeys", according to Wikelski.
However, the researchers do not yet know just how the young cuckoos find their way for the first time and how they later stick so precisely to their flight plan. For this, they must catch cuckoos, transport them to new locations without the animals being able to orientate themselves on the way, and release them again. The route taken can then provide clues on the orientation behaviour. In addition, the ICARUS research program, planned for 2015 on the International Space Station, should enable the tracking of more and smaller birds – and that with a thousand times greater precision.
In any case, the narrow flight corridors of the cuckoos are of great importance to the survival of the animals. Destruction of the habitats in the narrowly circumscribed intermediate stops, flight obstacles or intensive hunting can be a threat to the existence of entire populations. The protection of these corridors is similarly important to the preservation of the resting and breeding grounds of such prominent species as coastal birds, geese and cranes.