Muheim's experiments proved that seeing polarized light cues near the horizon was the critical factor. "Once the right hypothesis came along, it all fit," said Phillips.
The research provides support for an observation Phillips had published 20 years ago. In the mid 1980s, he was doing research to determine how homing pigeons navigated. There was a theory that wind-borne odors provide pigeons with information about the locations of odor sources, which could then be used to determine their position relative to the home loft when they were released at an unfamiliar site. The birds were housed in a loft with a "pinwheel" arrangement of deflector panels attached to the four screened walls of the loft to rotate direction of the wind. Pigeons housed in the so-called "deflector lofts" showed the predicted (clockwise or counterclockwise) deflection of homeward orientation when released at a distant site. It turned out, however, that the panels influenced the distribution of polarized light patterns at sunset and sunrise, and it was the altered polarization patterns, rather than olfactory cues, that produced the directional biases. Moreover, the effect appeared to result from recalibration of the sun compass. Phillips published the research in the Journal of Theoretical Biology (1988, volume 131). "I've felt every since that this was the key to understanding the integration of compass information in migratory birds" he said.