Pelagic seabirds wander the open oceans then return accurately to their habitual nest-sites. 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. A recent experiment on Atlantic shearwaters (Cory’s shearwater, Calonectris borealis) breeding in the Azores indicated a crucial role of olfaction over the open ocean, but left open the question of whether birds might navigate by topographical landmark cues when available. Our 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.

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The role of environmental olfactory information in pigeon navigation has been extensively studied by analysing vanishing bearing distributions and homing performances of homing pigeons subjected to manipulation of their olfactory perception and/or the olfactory information they were exposed to during transportation and at the release site. However, their behaviour during the homing flight remains undocumented. In this experiment we report the analysis of tracks of birds made anosmic at the release site by washing their olfactory mucosa with zinc sulfate. We thus can assess the role of local odours at the release site as well as the role of environmental odours perceived on the way, far from the release site. We observed that pigeons transported and kept at the release site in purified air and made anosmic at the release site were unable to orient towards home and were impaired at homing. By contrast, pigeons allowed to smell environmental odours during transportation and at the release site, although made anosmic prior to release, displayed unimpaired homeward orientation, but nevertheless showed impaired homing performance. These results are consistent with the view that local odours at the release site are critical for determining the direction of displacement (olfactory map) and suggest that pigeons consult the olfactory map also during their homing flight in order to be able to find their way home.

The avian hippocampal formation (HF) is thought to regulate map-like memory representations of visual landmarks/landscape features and has more recently been suggested to be similarly important for the perceptual integration of landmarks/landscapes. Aspects of spatial memory and perception likely combine to support the now well-documented ability of homing pigeons to learn to retrace the same route when homing from familiar locations, leading to the prediction that damage to the HF would result in a diminished ability to repeatedly fly a similar route home. HF-lesioned homing pigeons were repeatedly released from three sites to assess the importance of the hippocampus as pigeons gradually learn a familiar route home guided by familiar landmark and landscape features. As expected, control pigeons displayed increasing fidelity to a familiar route home, and by inference, successful perceptual and memory processing of familiar landmarks/landscape features. By contrast, the impoverished route fidelity of the HF-lesioned pigeons indicated an impaired sensitivity to the same landmark/landscape features.

The identification of year-round geographical ranges and the quantification of the degree of migratory connectivity are fundamental to the successful conservation of migratory bird populations. The Stone-curlew Burhinus oedicnemus is a species of conservation concern in Europe, but its ecology and behaviour are relatively poorly investigated. In particular, its migratory behaviour and the\ud locations of the wintering ranges of most European populations are not known in detail because of a lack of specific studies and the scarcity of ringing recoveries. This study aimed to identify the wintering areas of a Stone-curlew population breeding in the Taro River Regional Park (Parma, northern Italy) by integrating the information obtained from ringing recoveries (n = 2), geolocators\ud (n = 7), and GPS data loggers (n = 2). Furthermore, we compared two approaches to inferring the location of an assumed stationary bird using geolocator data. The different sources were quite coherent, indicating that tagged Stone-curlews did not leave the Mediterranean basin throughout the year and passed the winter in Sardinia or in Tunisia. The recorded wintering sites coincided with areas where breeding (and possibly resident) populations are reported, further emphasising the importance of these areas for the conservation of the species throughout the annual cycle. To\ud our knowledge, our study represents the first thorough analysis performed to uncover the movements of a Mediterranean population of Stone-curlews. Furthermore, it proves the great potential of the tracking devices used in this work to provide information on the migration and non-breeding sites of elusive species, for which the application of mark–recapture/re-sighting techniques is hindered by\ud profound limitations

The importance of the vertebrate hippocampus in spatial cognition is often related to its broad role in memory. However, in birds, the hippocampus appears to be more specifically involved in spatial processes. 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. 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.

Studying a species under a range of conditions is essential for fully understanding its ecology and for predicting its response to human impacts on the environment. We investigated the spatial behaviour and the habitat characteristics of foraging areas of Eurasian Stone-curlews breeding in an important but poorly investigated habitat, gravel riverbed, throughout the full 24-h cycle. The data collected for 17 radiotagged birds nesting in the Taro River Regional Park (Parma, Italy) showed a clear split between diurnal and nocturnal spatial behaviour. Almost all diurnal fixes and about two-thirds of nocturnal ones were located in the gravel riverbed, which not only provided suitable breeding territories but probably part of the food resources needed for reproduction. Nocturnal excursions from breeding sites to feeding areas (mostly farmland), sometimes of a few kilometres, indicated that these resources do not cover all of the birds' needs. Night spotlight counts of foraging birds in the agricultural area indicated that Stone-curlews preferred recently harvested crops (mainly forage and wheat) and piles of farmyard manure. These habitat preferences are closely linked to the predominant agricultural activity of the study area, which is characterized by a high density of dairy farms for the production of Parmigiano Reggiano cheese. It seems likely that the proximity of gravel riverbed and farmland habitats is one of the main causes of the high breeding density recorded in the study area. We propose that the conservation of Stone-curlews at this site could potentially be achieved only by a synergistic management of both natural and agricultural habitats.

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