HOMEWARD BOUND

Abstract

Homing pigeons' uncanny ability to navigate home depends on a dazzling array of cues, including the sun, smells and familiar landmarks. Pigeons appear to use both a topographical map of familiar landmarks and an internal compass bearing to navigate across familiar terrain. To assess the relative importance of the map and compass, Anna Gagliardo and colleagues from the University of Pisa decided to see what would happen if the birds' map information conflicted with their compass bearing(p. 469).Pigeons use the sun as a compass, so to confuse the birds' orientation the team shifted pigeons' circadian rhythms by keeping the birds in an artificial light-dark cycle, resulting in clock-shifted pigeons. The birds' sun compass now indicated a wrong homeward direction but familiar landmarks could still indicate the true homeward direction. The team released normal and clock-shifted pigeons from familiar and unfamiliar sites and recorded the pigeons' orientation before they took off as well as the direction they disappeared in. At familiar release sites, the team saw that birds with normal circadian rhythms, which were able to use their sun compass, were homeward oriented even before take-off and flew off in the direction of home. But clock-shifted pigeons were randomly oriented before take-off and did not vanish in a homeward direction. Clearly, the sun compass strategy is important, but this was not the end of the story. Clock-shifted birds released from familiar sites showed a smaller deflection from the homeward orientation than clock-shifted birds released from unfamiliar sites. So while clock-shifting deflected the birds from the true direction of home,familiarity with the site reduced this deflection, presumably because the birds use familiar landmarks to ensure that they are homeward bound.