Anosmia impairs homing orientation but not foraging behaviour in free-ranging shearwaters.

Shearwaters deprived of their olfactory sense before being displaced to distant sites have impaired homing ability but it is unknown what the role of olfaction is when birds navigate freely without their sense of smell. Furthermore, treatments used to induce anosmia and to disrupt magneto-reception in displacement experiments might influence non-specific factors not directly related to navigation and, as a consequence, the results of displacement experiments can have multiple interpretations. To address this, we GPS-tracked the free-ranging foraging trips of incubating Scopoli's shearwaters within the Mediterranean Sea. As in previous experiments, shearwaters were either made anosmic with 4% zinc sulphate solution, magnetically impaired by attachment of a strong neodymium magnet or were controls. We found that birds from all three treatments embarked on foraging trips, had indistinguishable at-sea schedules of behaviour and returned to the colony having gained mass. However, we found that in the pelagic return stage of their foraging trips, anosmic birds were not oriented towards the colony though coastal navigation was unaffected. These results support the case for zinc sulphate having a specific effect on the navigational ability of shearwaters and thus the view that seabirds consult an olfactory map to guide them across seascapes.

Testing cognitive navigation in unknown territories: homing pigeons choose different targets.

Homing pigeons (Columba livia) are believed to adopt a map-and-compass strategy to find their way home. Surprisingly, to date a clear demonstration of the use of a cognitive map in free-flight experiments is missing. In this study, we investigated whether homing pigeons use a mental map in which - at an unknown release site - their own position, the home loft and a food loft are represented simultaneously. In order to test this, homing pigeons were trained to fly to a 25-30 km distant food loft. A total of 131 hungry and satiated pigeons were then released from an unfamiliar site equidistant from the food loft and the home loft. Their vanishing bearings and homing times were assessed conventionally at four sites, and also their flight tracks from one release site by means of GPS loggers. The vanishing bearings of fed and hungry birds differed significantly at all release sites and a highly significant proportion of hungry birds flew to the food loft, while the fed birds headed home. The GPS experiment revealed a number of pigeons flying very precisely to the food loft, others correcting their flight direction after topography-induced detours. This implies that the pigeons knew their geographical position in relation to the targets, and chose a flight direction according to their locally manipulated needs - clearly the essence of a cognitive navigational map.