The Role of Visual Familiarity with the Landscape in Pigeon Homing

Abstract

In 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.

Orientation and Navigation in Vertebrates

“…Indeed, in many trials clock-shifted pigeons did not deviate as expected based on the clock shifts, but instead made "corrections" of their homeward routes. These corrections varied by degree, showing compromising directions in some cases, and no deflection in other (Wallraff et al 1994(Wallraff et al , 1999Gagliardo et al 1999Gagliardo et al , 2002Gagliardo et al , 2005. However, the majority of the clock-shift setups by these and some other authors have involved occlusion of the olfactory sense.…”

“…These definitions were primarily aimed at determining how exactly landmarks may be used for short-range navigation, and Lohmann and Lohmann 1996b) there has been much debate over the topic. Today, the most widely accepted understanding of piloting (see Wallraff and Neumann 1989;Wallraff et al 1994;Holland 2003) is related to the concept of mosaic maps (spatial representation of familiar terrains with irregularly distributed prominent objects). The simplest explanation of the notion is that piloting is the use of local landmarks, the spatial relationships among which are remembered by an animal and employed to deduce the location of a remote goal within a familiar area.…”

Songbirds use scent cues to relocate to feeding sites after displacement: An experiment in great tits (Parus major)

“…Great tits display strong site fidelity and were shown to return to their winter feeding grounds even after displacement of up to 7.8 km (Krištín and Kaňuch, 2017). Therefore, although given the predominant visual competences of birds and their familiarity with the local environment (Wallraff et al, 1994), we expect resident great tits to relocate to the feeders, independently of their olfactory capacities. This is also based on previous findings in starlings, demonstrating no differences in the return rates between control and olfaction-deprived individuals released in vicinity to their nesting grounds (Wallraff et al, 1995).…”