• olfactory information
• GPS
• landmark
• geomagnetic information
• pigeon navigation

This projects aims at investigating the nature of the stimuli used in homing pigeons’ navigation over both unfamiliar and familiar areas by using GPS technology. The novel approach of this research project consisted in the investigation of old open questions by means of the use of the satellite technology. While the classical methods of investigation consisted in recording the initial orientation of birds at the release site and their homing time and success, the use of GPS loggers enabled the collection of detailed information on the behaviour of the pigeon during the entire homing journey. The analysis of the whole homing flight of birds subjected to experimental manipulations has highlighted behaviours and phenomena otherwise undetectable with traditional experiments.
As concerning the true navigation behaviour, three investigations have been conducted: the olfactory lateralization in homing pigeons, the role of environmental odours on the navigational map and the role of geomagnetic information in a position finding mechanism.
As regarding the analysis of the homing flight path of experienced pigeons receiving a unilateral olfactory input, the use of GPS-technique has allowed to highlight some of the effects of the right nostril occlusion, which remained undetected when observing only the initial orientation of the birds at vanishing. We have analysed the tracks of birds released with the left or the right nostril occluded and we have highlighted an important functional asymmetry in favour of the right nostril. In fact the birds processing the environmental olfactory information with the left nostril only, displayed a higher level of tortuosity in their flight path and stopped more frequently than both the unmanipulated controls and the birds using the right nostril.
A further progress in the analysis of the birds navigational capabilities from unfamiliar places has been possible thanks to a newly developed GPS data loggers, that allows for a remote readout of the stored data, enabling therefore the acquisition of data of birds that do not home. With this specific technology we achieved a major advance in the understanding of the role of olfactory stimuli in pigeon navigation as we could test the performances of birds made anosmic by nasal anaesthesia. By using this kind of GPS we could test the olfactory activation hypothesis that predicts that olfactory stimuli prime the navigational capabilities of birds, and that the environmental odours are solely needed to activate a navigational system that, in turn, is based on non-olfactory cues. This hypothesis challenges the olfactory navigation hypothesis, which predicts that environmental odours constitute a specific component of the navigational map in homing pigeons. Therefore, we have analysed the GPS tracks of three groups of pigeons subjected to different olfactory conditions during transportation and at the release site and subjected to nasal anaesthesia prior release: controls birds exposed to environmental odours, birds transported in pure air and pigeons transported in pure air but stimulated with artificial odour of plant origin, before the release. The analysis of the tracks revealed that the birds exposed to the artificial odours displayed significantly poorer navigational performances than controls, suggesting a specific role of environmental olfactory information in pigeon navigation.
Anatomical studies and conditioning experiments provided evidence that pigeons detect geomagnetic field intensity through the ophthalmic branch of the trigeminal nerve. Despite the fact that magnetic treatments and trigeminal nerve section do not disrupt the abilities of pigeons to home back to the colony, it has been proposed that pigeons tend to fly parallel or perpendicular to the steepest magnetic slope. We have analysed tracks of both intact and trigeminal sectioned pigeons in order to test if the pattern of the local magnetic gradient affect the birds’ flight paths. The analysis did not reveal a consistent effect of the local geomagnetic field in the birds’ homing trajectories.
As concerning the navigation from familiar locations, we have conducted an investigation about the role of the topography in the landmark based navigation over familiar areas.
It is known that pigeons are able to memorise landscape features of the over-flown areas. These features can be associated to a specific compass direction leading the bird home (site specific compass orientation). Alternatively the bird can learn the spatial relationships among the single landmarks so to build a familiar landmark based map used in a piloting strategy. The two different strategies can be put in conflict by shifting the birds’ internal clock, in order to asses which of the two strategies is preferentially adopted by the subject. This protocol has been used to assess which factors are determining the strategy preferentially used by an individual pigeon and the kind of landscape feature which are likely to be memorised as landmarks during piloting. The analysis of the tracks suggested that the characteristic features of the release site affect the level of reorientation after clock shift, and, in particular, it emerged that the sea might represent an important topographical feature, probably due to its strong chromatic component, that facilitates the ability of the birds to re-orient after a phase shift treatment. Therefore, the vicinity of the sea seems to determine a preference for the piloting strategy.