Homing Pigeons Smell the Wind to Find Home

Homing pigeons use atmospheric conditions such as odor and wind to construct the mental "map" they rely on to find their way home, according to a new study published in the journal Biogeociences.

The birds navigate using the Sun and Earth's magnetic field, but atmospheric clues are used to fine-tune the pigeon's flight path, the new research suggests.

Hans Wallraff of the Max Planck Institute for Ornithology in Seewiesen, Germany, has been studying pigeons for years. In a previous study, Wallraff collected air samples at nearly 100 sites within a 200 kilometer radius of a former pigeon loft in southern Germany.

By analyzing the air samples, Wallraff learned that there are certain ratios among the odorous volatile organic compounds in the air that increase or decrease along specific directions.

A change of the compound ratios equates to a perceivable change in smell for the birds, Wallraff learned, concluding that the birds could navigate home based on the change in direction of the perceived smell. He went on to form a hypothesis:

"If the percentage of compound A increases with southerly winds, a pigeon living in a loft in Würzburg learns this wind-correlated increase. If released at a site some 100 km south of home, the bird smells that the ratio of compound A is above what it is on average at its loft and flies north," Wallraff explained.

To test his theory, Wallraff designed "virtual" pigeons, with knowledge of winds and odors only at their home nest. The virtual birds were able to find their way back home using atmospheric data, Wallraff found.

"My virtual pigeons served as tools to select those volatile compounds whose spatial distributions, combined with variations dependent on wind direction, were most suitable for homeward navigation," he said.

"Work with real pigeons was the beginning of the story. In this research, I wanted to find out whether and in what way the chemical atmosphere fulfills the demands for avian navigation. Eventually, to identify the chemical compounds birds actually use for home-finding, we will need real birds again. But this is far in the future."