Landmark-based navigation in birds: learning and using topographical cues

This projects aims at understanding the role of visual cues in birds’ navigation and the involvement of the two brain hemispheres in processing familiar topographical landmarks by using GPS technology. The maturing of GPS-tracking technology has enabled a revolution in navigation research, including the expanded possibility of studying brain mechanisms that guide navigation in the field. The GPS technology allowing the reconstruction of birds’ flight paths across the landscape with remarkable precision has been enhanced the research on landmark-based navigation in the last decade. Although familiar landmark-based navigation has been extensively studied, the use of familiar topographical features in wild birds’ navigation is still poorly understood. A crucial role of olfaction in oceanic navigation has been recently indicated in Cory’s shearwaters (a pelagic seabird), but whether seabirds might navigate by relying on topographical cues is still an open question. In this project three investigations have been conducted: i) the role of the environmental stimuli on Mediterranean navigation of Scopoli's shearwaters; ii) functional asymmetries in the visual system of pigeons in landmark-based spatial learning during homing; iii) involvement of the hippocampal formation in processing and using landscape visual cues. As concerning seabirds navigation, we investigated the effects of sensory manipulation on oceanic navigation in Scopoli’s shearwaters (Calonectris diomedea) breeding at Pianosa island (Italy), by displacing them 400 km from their colony and tracking them. The experiment was conducted in the Mediterranean sea, where the availability of topographical cues may provide an alternative navigational mechanism for homing. Magnetically disturbed shearwaters and control birds oriented homeward even when the coast was not visible and rapidly homed. Anosmic shearwaters oriented in a direction significantly different from the home direction when in open sea. After having approached a coastline their flight path changed from convoluted to homeward oriented, so that most of them eventually reached home. Beside confirming that magnetic cues appear unimportant for oceanic navigation by seabirds, our results support the crucial role of olfactory cues for birds’ navigation and reveal that anosmic shearwaters are able to home eventually by following coastal features. Several studies in laboratory settings showed hemispheric specializations in visual tasks in birds. However, functional brain asymmetries in spatial behaviours in natural settings are still poorly investigated. We trained homing pigeons with a monocular occlusion (LH and RH with left eye and the right eye occluded and therefore processing the visual stimuli with the left and the right hemisphere, respectively) and unmanipulated control birds from two release sites. The monocular pigeons showed diminished tendency to fly in group in comparison to the control birds. However, the RH showed a stronger tendency to fly alone compared to the LH pigeons. In addition the RH birds displayed a higher fidelity to their most efficient route and were more efficient in localising home in the last phase of the homing process. After a clock-shift treatment when released in binocular condition, the birds of the three groups displayed a similar pattern of deviation from the last training track. However the RH birds showed a higher fidelity to the corridor identified by the tracks recorded during the last single training release in un-shifted condition. By contrast, the LH birds before re-orienting tended to fly for longer distances outside the previously visited area, compared to the RH birds. Our data suggest that there might be an advantage of the right hemisphere in memorising and using topographical cues in a re-orientation task during homing after clock-shift. Research in homing pigeons showed that the hippocampal formation (HF) is involved in familiar landmark-based navigation, while it seemed to play no role in navigation over unfamiliar space. By GPS-tracking homing pigeons released from distant, unfamiliar sites prior to and after hippocampal lesion, we observed, as has been reported previously, impaired navigational performance post-lesion over the familiar/memorized space near the home loft, where topographic features constitute an important source of navigational information. The GPS-tracking revealed that many of the lost pigeons, when lesioned, approached the home area, but nevertheless failed to locate their loft. Unexpectedly, when they were hippocampal-lesioned, the pigeons showed a notable change in their behaviour when navigating over the unfamiliar space distant from home; they actually flew straighter homeward-directed paths than they did pre-lesion. The data are consistent with the hypothesis that, following hippocampal lesion, homing pigeons respond less to unfamiliar visual, topographic features encountered during homing, and, as such, offer the first evidence for an unforeseen, perceptual neglect of environmental features following hippocampal damage.