After foraging out in the open ocean, seabirds like albatrosses and shearwaters are able to find the way back to their colonies with astounding accuracy. Exactly how do they pinpoint their tiny, remote island homes across vast expanses of featureless seascapes? Researchers have proposed ideas ranging from magnetic cues to landmarks based on local odors. Now, a team studying the movements of GPS-tagged seabirds reveal that it’s all in the nose: They rely on olfactory maps. The work was published in Proceedings of the Royal Society B last week.
Previous homing studies have suggested that shearwaters navigate by assembling cognitive maps of wind-borne odors, but this has never been properly tested. Experiments with wild birds involving invasive sensory manipulation sort of defeats the purpose.
For a non-invasive approach, Rothamsted Research’s Andrew Reynolds and colleagues attached little, high-resolution GPS loggers to 210 shearwaters from three species: Cory's shearwaters (Calonectris borealis) in the North Atlantic Ocean, Scopoli's shearwaters (C. diomedea) in the Mediterranean Sea, and Cape Verde shearwaters (C. edwardsii) in the Central Atlantic Ocean. These adult birds were tagged during incubation or chick rearing, and the data loggers were removed after one foraging trip.
The team found that the flight patterns of 69% of the shearwaters are consistent with what they’d expect if the birds were indeed using olfactory-cued navigation when there’s turbulence in the atmosphere. In other words, the shearwaters aren’t making a beeline toward their colony: They change directions as they’re guided by scents, resulting in a cluster of movements.
You can see how olfactory navigation works in the sketch to the right. The black arrows represent displacements. Since they associate smells to wind directions, a bird knows that when it’s on the colony, blue and yellow odors emanate from the east and the north, respectively. The darker colors aren’t islands, by the way. These represent areas where the bird is able to orientate. So, if a bird at Point S wants to head home, it will fly westward. But because of atmospheric turbulence, blue odor isn’t always present at detectable concentrations, so the bird changes orientation in order to relocate the cue. And when it does, it resumes flying westward. If it arrives in an area where yellow odor dominates, it knows to head southward. Once it’s close, the bird might start using landmarks, other birds, or unique colony odors to guide itself home.
Middle Image: A.M. Reynolds et al./Proc. R. Soc. B 2015 .