How Pigeons May Smell Their Way Home

Homing pigeons, like other birds, are extraordinary navigators, but how they manage to find their way back to their lofts is still debated. To navigate, birds require a ‘map’ (to tell them home is south, for example) and a ‘compass’ (to tell them where south is), with the sun and the Earth’s magnetic field being the preferred compass systems. A new paper provides evidence that the information pigeons use as a map is in fact available in the atmosphere: odors and winds allow them to find their way home. The results were published online on November 4, 2013 in Biogeosciences, an open-access journal of the European Geosciences Union (EGU). Experiments over the past 40 years have shown that homing pigeons get disoriented when their sense of smell is impaired or when they don’t have access to natural winds at their home site. But many researchers were not convinced that wind-borne odors could provide the map pigeons need to navigate. Now, Dr. Hans Wallraff of the Max Planck Institute for Ornithology in Seewiesen, Germany, has shown that the atmosphere does contain the necessary information to help pigeons find their way home. In previous research, Dr. Wallraff collected air samples at over 90 sites within a 200 km radius around a former pigeon loft near Würzburg in southern Germany. The samples revealed that the ratios among certain ‘volatile organic compounds’ (chemicals that can be a source of scents and odors) in the atmosphere increase or decrease along specific directions. “For instance, the percentage of compound A in the sum A+B or A+B+C+D increases the farther one moves from north to south,” Dr. Wallraff explains. These changes in compound ratios translate into changes in perceived smell. But a pigeon that has never left its loft does not know in what directions what changes occur – unless it has been exposed to winds at its home site.