Within minutes of breaking out of their shells, newly hatched loggerhead turtles embark on what is possibly the longest known migration. Spanning entire ocean basins, crossing barren dead zones and verdant ocean frontal systems, the young voyagers must rapidly identify and fill up in lush foraging grounds in preparation for leaner times ahead. So how do these turtles identify fertile foraging grounds? Explaining that loggerheads dine on jellyfish – which congregate to feast on colossal photyplankton blooms – Courtney Endres and Ken Lohmann from the University of North Carolina at Chapel Hill, USA, add that the photoplankton release a distinctive odour, dimethyl sulphide (DMS), into the air when consumed. As other oceanic foragers are known to home in on this scent when pursuing prey, the duo decided to test whether loggerhead turtles can also pick up the odour of DMS (p. 3535).
Allowing 5-month-old juveniles to swim in an open arena, Endres and Lohmann flooded the airspace above the water with odours ranging from jasmine, cinnamon and lemon to DMS, as well as unscented water, and filmed the youngsters' responses to find out whether they responded to novel odours or specifically to DMS.
Having invited Stacy Zhang and Julie Gassmann to count how long each turtle poked its nose above the surface, it was clear that the turtles spent significantly more time sniffing the DMS odour than the novel odours wafting over them. ‘The failure of turtles to respond to cinnamon, jasmine and lemon odours implies that the response elicited by DMS is not a generalized response to all novel airborne odorants’, the duo says.
Suggesting that DMS odour could help the turtles to identify foraging areas and remain within them, the duo is keen to find out whether the reptiles actively exploit the cue and whether they use other odours to keep them on track during their vast odyssey.