Olfactory navigation
Papi's mosaic model proposes that pigeons construct a map from the distribution of environmental odours, within a radius of 70–100 kilometres.
[4] In 1972, however, Papi and his contemporaries reported that anosmic pigeons (Columbia livia) were severely impaired in orientation and homing performance.
Therefore, homing is viable only if the release sites are within a proximity that can provide reliable wind-borne cues,[8] although Papi (1990),[5] argues the utilisation of olfactory information obtained during the outward journey.
Odour gradient differs along dissimilar directional axes and, therefore, the pigeon can compare the intensity of the scent at a particular location to its concentration at the home loft.
The olfactory navigation hypothesis states that pigeons learn an odour map by associating smells perceived at the home loft with the directions from which they are carried by winds.
However, it is important to note that there has been a failure to replicate these results in other countries, such as Germany, Italy and the United States, even when considerable effort has been made to employ identical procedures.
The wind reversed experiments, too, exhibited results that favoured the olfactory hypothesis, with experimentals on average flying in the opposing direction of home, while the controls took the correct flight path, when released from the same site.
In replication of the deflector loft experiments, similar findings were produced,[14][15] though when anosmic pigeons where employed, they displayed the same degree of error in orientation as had previously been observed.
[3][11] Researchers support these suggestions[16] by noting the lack of highly developed nasal apparatus and associated brain functions in seed-eating birds such as pigeons.
This first indication for magnetic compass orientation in homing was later supported by other studies,[20][21] which reversed the field around the head of the pigeon using battery operated coils.
Another observation consistent with the idea of a geomagnetic map is the shift in the initial bearings of pigeons that occurs when the field increases during magnetic storms.
[8] Experiments to test this hypothesis, using the migratory European starling, indicated that the direction of migration could be manipulated by reflecting the angle of the Sun.
[citation needed] Odour may still, however, be one of many navigational factors playing a highly variable role, though physical limitations and inconsistent findings render the olfactory hypothesis questionable.
