Homing pigeons taken from their lofts and released as far away as 1,000 km in unfamiliar territory return home. Kramer (1953)
proposed the idea of dividing the homing process into two components, "map," the determination of the direction toward home, and "compass," the process of flying in that direction. Wiltschko and Wiltschko (2003)
have provided a superb review of the historical development of our understanding of how birds home. Yet as they point out in their review, the cues that pigeons use to determine the direction to the home loft (the "map") are still controversial. Olfactory cues play some role in determining the direction to home, but it seems unlikely that they are the only important cue. Once the direction to home is determined, either the sun, the earth's magnetic field or both together serve as directional or compass cues. Near the loft itself, it seems likely that familiar visual landmarks are important. Thus pigeon homing depends on a variety of cues; the question discussed in this paper is how does a pigeon choose which cue to use and are there interactions between the different sensory modalities?