Gaia Dell'Ariccia

Long flights and age affect oxidative status of homing pigeons (Columba livia)

SUMMARY Flying is an energy demanding activity that imposes several physiological challenges on birds, such as increase in energy expenditure. Evidence from sports medicine shows that exhausting exercise may cause oxidative stress. Studies on avian flight have so far considered several blood parameters, such as uric acid, corticosteroids, or circulating free fatty acids, but only one study has analysed markers of oxidative stress in flying birds. In this study, we evaluated, for the first time, how different flight efforts affect the oxidative status using homing pigeons (Columba livia) as a model species. Two groups of pigeons flew for around 60 and 200 km, respectively. Pigeons that flew for 200 km had a 54% increase in oxidative damage as measured by serum reactive oxygen metabolites (ROMs), a 19% drop in total serum antioxidant capacity (OXY) and an 86% increase of oxidative stress (ROMs/OXY×1000). Older pigeons depleted more serum antioxidants regardless of the release distance. Among pigeons that flew the longer distance, heavier ones depleted less serum antioxidants. The results of the study suggest that long flights may cause oxidative stress, and that older individuals may experience higher physiological demands.

EEG Responses to Visual Landmarks in Flying Pigeons

BACKGROUND GPS analysis of flight trajectories of pigeons can reveal that topographic features influence their flight paths. Recording electrical brain activity that reflects attentional processing could indicate objects of interest that do not cause changes in the flight path. Therefore, we investigated whether crossing particular visual landmarks when homing from a familiar release site is associated with changes in EEG. RESULTS Birds carried both data-loggers for recording GPS position and EEG during flight. First, we classified characteristic EEG frequencies of caged birds and found five main bands: A: 0-3, B: 3-12, C: 12-60, D: 60-130, and E: 130-200 Hz. We analyzed changes in these activity bands when pigeons were released over sea (a featureless environment) and over land. Passing over the coastline and other prominent landmarks produced a pattern of EEG alterations consisting of two phases: activation of EEG in the high-frequency bands (D and/or E), followed by activation of C. Overlaying the EEG activity with GPS tracks allowed us to identify topographical features of interest for the pigeons that were not recognizable by distinct changes of their flight path. CONCLUSIONS We provide evidence that EEG analysis can identify landmarks and objects of interest during homing. Middle-frequency activity (C) reflects visual perception of prominent landmarks, whereas activation of higher frequencies (D and E) is linked with information processing at a higher level. Activation of E bands is likely to reflect an initial process of orientation and is not necessarily linked with processing of visual information.

Flock flying improves pigeons' homing: GPS track analysis of individual flyers versus small groups

The effects of aggregation in navigating animals have generated growing interest in field and theoretical studies. The few studies on the effects of group flying on the performance of homing pigeons, Columba livia, have led to controversial conclusions, chiefly because of the lack of appropriate technology to follow pigeons during their entire homeward flight. Therefore, we used GPS data loggers on six highly trained pigeons from a familiar release site first by releasing them six times individually, then six times as a group from the same site, and, finally, again six times individually. Flight data showed that the homing performance of the birds flying as a flock was significantly better than that of the birds released individually. When flying in a flock, pigeons showed no resting episodes, shorter homing times, higher speed, and almost no circling around the start zone in comparison to individual flights. Moreover, flock-flying pigeons took a nearly direct, ‘beeline’ route to the loft, whereas individually flying birds preferred to follow roads and other longitudinal landmarks leading towards the loft, even when it caused a detour. Our results show that group cohesion facilitates a shift towards more efficient homing strategies: individuals prefer navigating by familiar landmarks, while flocks show a compass orientation.

Olfactory foraging in temperate waters: sensitivity to dimethylsulphide of shearwaters in the Atlantic Ocean and Mediterranean Sea

Many procellariiforms use olfactory cues to locate food patches over the seemingly featureless ocean surface. In particular, some of them are able to detect and are attracted by dimethylsulphide (DMS), a volatile compound naturally occurring over worldwide oceans in correspondence with productive feeding areas. However, current knowledge is restricted to sub-Antarctic species and to only one study realized under natural conditions at sea. Here, for the first time, we investigated the response to DMS in parallel in two different environments in temperate waters, the Atlantic Ocean and the Mediterranean Sea, employing Corys (Calonectris borealis) and Scopolis (Calonectris diomedea) shearwaters as models. To test whether these birds can detect and respond to DMS, we presented them with this substance in a Y-maze. Then, to determine whether they use this molecule in natural conditions, we tested the response to DMS at sea. The number of birds that chose DMS in the Y-maze and that were recruited at DMS-scented slicks at sea suggests that these shearwaters are attracted to DMS in both non-foraging and natural contexts. Our findings show that the use of DMS as a foraging cue may be a strategy adopted by procellariiforms across oceans but that regional differences may exist, giving a worldwide perspective to previous hypotheses concerning the use of DMS as a chemical cue.

Back home at night or out until morning? Nycthemeral variations in homing of anosmic Cory's shearwaters in a diurnal colony

SUMMARY Olfactory cues have been shown to be important to homing petrels at night, but apparently those procellariiform species that also come back to the colony during the day are not impaired by smell deprivation. However, the nycthemeral distribution of homing, i.e. whether displaced birds released at night return to their burrow by night or during daylight, has never been investigated. To explore this question, we studied the homing behaviour of Corys shearwater (Calonectris borealis) in the only known population where these birds are active at the colony both during the day and at night. Here, we compared the nocturnal versus diurnal homing schedule of birds treated with zinc sulphate (to induce a reversible but complete anosmia) with that of controls. Our results show that anosmic shearwaters were unable to home in the dark and were constrained to wait for the daylight to find their burrow again. Our results confirm that olfaction is the basic sensory input for homing by night even in a petrel species that is diurnally active at the colony.

Testing cognitive navigation in unknown territories: homing pigeons choose different targets

SUMMARY Homing pigeons (Columba livia) are believed to adopt a map-and-compass strategy to find their way home. Surprisingly, to date a clear demonstration of the use of a cognitive map in free-flight experiments is missing. In this study, we investigated whether homing pigeons use a mental map in which – at an unknown release site – their own position, the home loft and a food loft are represented simultaneously. In order to test this, homing pigeons were trained to fly to a 25–30 km distant food loft. A total of 131 hungry and satiated pigeons were then released from an unfamiliar site equidistant from the food loft and the home loft. Their vanishing bearings and homing times were assessed conventionally at four sites, and also their flight tracks from one release site by means of GPS loggers. The vanishing bearings of fed and hungry birds differed significantly at all release sites and a highly significant proportion of hungry birds flew to the food loft, while the fed birds headed home. The GPS experiment revealed a number of pigeons flying very precisely to the food loft, others correcting their flight direction after topography-induced detours. This implies that the pigeons knew their geographical position in relation to the targets, and chose a flight direction according to their locally manipulated needs – clearly the essence of a cognitive navigational map.

The influence of experience in orientation: GPS tracking of homing pigeons released over the sea after directional training.

SUMMARY Flight experience is one of the factors that influences initial orientation of displaced homing pigeons (Columba livia). Prior studies showed a systematic dependence of initial orientation on previously flown direction. Using GPS data loggers, this study sought to examine the effect of previous directional training of 40 homing pigeons when they were released over the sea, in the absence of proximal landmarks, in a direction almost perpendicular to that of previous training flights. Our results demonstrated that previous directional training evoked a systematic and predicted deviation from the beeline over the sea that appeared as a compromise between the direction of training and the direction to the loft. Pigeons were able to efficiently correct their flight direction only once over land, where they flew significantly slower and less directly than over the sea.

First GPS-tracking of Cory's shearwater in the Mediterranean Sea

Abstract The behaviour and ecology of seabirds such as albatrosses, petrels and shearwaters have been the subject of numerous studies, often employing the most recent technologies to track birds during their foraging trips. Until now, however, large oceanic species have been preferred for tracking studies because of the dimensions and weight of the devices available. New light-weight GPS (Global Positioning System) loggers (< 9 g) were used to track foraging trips of a medium-sized species, the Corys shearwater, for the first time in the Mediterranean Sea. The tracks obtained showed that Mediterranean Corys shearwaters alternatively used one of two different fishing areas. Various explanations could account for this difference; one of these could be that the two directions have a different relevance for the birds, being for chick- and self-provisioning. This study provides new hypotheses concerning the behaviour of Corys shearwaters in the Mediterranean Sea, a different environment compared to previously studied oceans.