A whiff of home

Abstract

Researchers have revealed numerous cues animals use for quite extraordinary migrations across land and sea from stellar, solar, magnetic and other environmental sources. But cues used by one animal to locate one tiny island in the middle of the Atlantic Ocean from thousands of kilometres away, a puzzle noted by Darwin, has remained unsolved. But new work by a team of researchers from the University of Wales Swansea, Lund University and the University of Pisa reported in the biology letters of the Proceedings of the Royal Society (published online), suggests that the island's smell may provide vital cues for homebound turtles. Green turtles (Chelonia mydas) migrate from their grazing grounds off the coast of Brazil in their thousands to the beaches of Ascension Island more than 2,000 kilometres away to mate and lay eggs. Efforts to determine how they achieve this navigational feat have been stymied by the sheer technical difficulties. Adults off Brazil do not come ashore so are hard to locate and individuals only return to Ascension Island once every three or four years. Also the population off Brazil includes individuals that breed at other locations so that captured and tagged individuals may not be those originating from the tiny Atlantic island. To try to overcome these problems the team captures six individuals who had just laid their first clutch of eggs on the island – they often lay multiple clutches so were likely to wish to return – and placed three 50 kms upwind of the island and three 50 kms downwind. Satellite transmitters were attached to the animals' carapace to study their movements. The team found that the individuals released downwind had no difficulty returning to the island within a few days but those upwind had much more difficulty, with two returning after 10 and 27 days and the third heading back to Brazil after failed efforts to relocate the island. The authors believe their results suggest that wind-borne smells may be crucial for the turtles' final ability to find home but that other cues may also be necessary for them to head off on the right track first. ‘Even if they routinely use wind-borne information… for the final approach to the target, it is unknown how they manage to reach this area,’ the authors report.