The Role of Visual Familiarity with the Landscape in Pigeon Homing

Abstract

AbstractIn an introductory discussion it is argued why a topographical ‘pattern map’ based on a familiar visual landscape should come into conflict with an angular shift of the sun compass, whereas a ‘point map’ based on atmospheric odours is expected to be freely rotatable by compass shifts. To test whether these predictions are met, releases were conducted in a familiar area with pigeons whose circadian clock was shifted 6 h forward. Half of the pigeons were prevented from smelling natural airborne odours by air filtration before release and nasal anaesthesia upon release. Analysis of initial bearings, also including earlier releases in unfamiliar areas, led to the following results. (1) Unfamiliar area, olfaction unimpaired (only assumed point map applicable): full deflection of bearings according to the amount of sun‐compass shift. (2) Familiar area, olfaction unimpaired (both point map and pattern map applicable): average deflection of bearings somewhat smaller than compass shift. (3) Familiar area, no olfactory access to natural air (only assumed pattern map applicable): average deflection of bearings only about half compass shift; increased variability. Corresponding non‐shifted controls were always homeward orientated.Results support the hypothesis that pigeons in a familiar area, if relying exclusively on non‐olfactory spatial information, utilize the visible landscape to find the way home. Certainly they also do so under normal conditions when additionally available airborne odours co‐determine behaviour, so that the investigator is unable to separate the roles of vision and olfaction. This most plausible and parsimonious hypothesis should be falsified before consideration of alternative hypotheses suggesting there are some mysterious unknown factors at work. How pigeons may view and evaluate the landscape for orientation over longer distances is briefly discussed.