Orientation in “Featureless” Environments: the Extreme Case of Pelagic Birds

During the breeding period, pelagic birds such as petrels and penguins commute between their colony and distant foraging grounds. Like migrating birds, they are able to travel large distances to reach suitable environmental conditions and/or food supplies. To accomplish their astonishing foraging trips, they should dispose of similar navigation capacities. Pelagic birds present a particular interesting example of animals that are challenged by orientation in an apparently featureless environment. Individuals travel over vast stretches of open ocean without landmarks. Several mechanisms have been proposed to explain the orientation mechanism of pelagic birds, yet the problem remains far from solved. In the past decade, the development of microelectronics provided excellent opportunities to follow individual birds using data-loggers and, to a greater extent, satellite tracking. Although technological advances have considerably decreased the weight of tracking devices, the number of species tracked is still limited. For pelagic birds, core investigations have been conducted on larger species of penguins and petrels. To date, all studies employing satellite telemetry on these birds have investigated spontaneous movements, and, with few exceptions, their aim was to investigate feeding ecology with little or no attention to possible orientation mechanisms. The first detailed tracking study of a pelagic bird was made in the Southern Indian Ocean, on wandering albatrosses, Diomedea exulans (Jouventin and Weimerskirch 1990). This study initiated a large body of works that revealed the impressive journeys performed by pelagic birds during the breeding period. Foraging trips are of particular interest to formulate hypotheses on orientation mechanisms, because birds must pinpoint a small target after a long journey. For example wandering albatrosses leave their small breeding island to set out on flights that take them over distances of several thousands of kilometres over several weeks, foraging in all quadrants around the island both en route and at their destination (Weimerskirch et al. 1993, 1994). After such foraging trips over foggy and raging oceans, however, they are able to return to their home with surprising precision. White_____________ 1 CEFE-CNRS, Behavioural Ecology Group, 34293 Montpellier cedex 5, France, e-mail: francesco. [email protected].