Evidence for a critical role of olfactory cues for homing after displacement in open ocean.
Procellariiformes are pelagic birds which wander in the open sea most of the year and often nest in remote oceanic islands. These birds are able to pinpoint their breeding sites following straight routes even if their nesting island is located within a homogeneous environment such as the open ocean.
Previous studies have shown that magnetic cues are irrelevant during foraging trips of albatrosses flying to feeding grounds and back to the colony, for oceanic navigation after displacement in white chinned petrels (Procellaria aeqiuinoctialis) and for the homing journeys of Cory’s shearwaters (Calonectris diomedea diomedea) after a displacement in the Mediterranean sea, where the use of visual topographical features cannot be excluded.
On the other hand the use of olfactory cues in locating the burrow within the colony, therefore in a short range navigation task, has been demonstrated in several species. Therefore the nature of the cues used to perform a true oceanic navigation task still remains unknown.
The present study aims to investigate the role of geomagnetic and olfactory information in the oceanic navigation of the Atlantic Cory’s shearwater (Calonectris diomedea borealis) after passive displacement in open ocean, where visual landmarks cannot be used for navigation. During the incubation period 12 birds nesting in the colony of Capelinhos, at Faial Island in the Azores archipelago (North Atlantic Ocean) were captured, embarked on a cargo ship travelling from Faial to Lisbon and displaced 500-600 km East in open ocean.
Prior to transportation the experimental manipulation took place: four birds were subjected to magnetic disturbance by gluing on their head a small box containing a mobile magnet; four birds were made anosmic by washing their olfactory mucosa with a 4% zinc sulphate solution; the last four birds were unmanipulated controls.
The control and the magnetically disturbed shearwaters were equipped with GPS data loggers, while the anosmic petrels were provided with satellite transmitters with GPS receiver. Both the unmanipulated birds and those subjected to magnetic disturbance oriented westward soon after release and, moving within a quite narrow and straight corridor, reached the archipelago in less than one week after the displacement. On the contrary, none of the anosmic birds was able to home. Soon after release, their tracks were oriented in a different direction than the Azores. Although two tags stopped transmitting the data, the tracks of the two other birds have documented an impressive journey of thousands of kilometres wandering over large oceanic areas distant from the Azores archipelago. Our data provide a preliminary evidence for a critical role of olfactory cues in long-distance oceanic navigation in Cory’s shearwaters and confirm that magnetic disturbance does not impair procellariiformes’ navigational abilities.
P Lambardi1, F Bonnadonna2, P Luschi3, J Bried1, P M Wikelski4, A Gagliardo3 1University of the Azores, Portugal, 2CNRS – CEFE, France3 University of Pisa, Italy, 4Max Planck Institute for Ornithology, Germany