Homing in pelagic birds: a pilot experiment with white-chinned petrels released in the open sea

During the breeding period white-chinned petrels (Procellaria aequinoctialis) repeatedly perform long foraging trips in the open ocean from their breeding island, and are able to home with an astonishing precision. The orientation mechanisms involved are not yet known. By analogy with those used by desert ants moving in a similarly "featureless" environment, one can hypothesise that petrels may home using path-integration. We displaced 11 white-chinned petrels 725-785km from their burrows to the open sea, preventing them from using visual and magnetic route-based information. Three birds carried satellite transmitters. Our results showed that they can home rather efficiently in such conditions.     

The role of geomagnetic cues in green turtle open sea navigation

Background

Laboratory and field experiments have provided evidence that sea turtles use geomagnetic cues to navigate in the open sea. For instance, green turtles (Chelonia mydas) displaced 100 km away from their nesting site were impaired in returning home when carrying a strong magnet glued on the head. However, the actual role of geomagnetic cues remains unclear, since magnetically treated green turtles can perform large scale (>2000 km) post-nesting migrations no differently from controls.

Methodology/Principal Findings

In the present homing experiment, 24 green turtles were displaced 200 km away from their nesting site on an oceanic island, and tracked, for the first time in this type of experiment, with Global Positioning System (GPS), which is able to provide much more frequent and accurate locations than previously used tracking methods. Eight turtles were magnetically treated for 24–48 h on the nesting beach prior to displacement, and another eight turtles had a magnet glued on the head at the release site. The last eight turtles were used as controls. Detailed analyses of water masses-related (i.e., current-corrected) homing paths showed that magnetically treated turtles were able to navigate toward their nesting site as efficiently as controls, but those carrying magnets were significantly impaired once they arrived within 50 km of home.

Conclusions/Significance

While green turtles do not seem to need geomagnetic cues to navigate far from the goal, these cues become necessary when turtles get closer to home. As the very last part of the homing trip (within a few kilometers of home) likely depends on non-magnetic cues, our results suggest that magnetic cues play a key role in sea turtle navigation at an intermediate scale by bridging the gap between large and small scale navigational processes, which both appear to depend on non-magnetic cues.     

Home‐site fidelity and homing behavior of the big‐headed turtle Platysternon megacephalum

Site fidelity refers to the restriction of dispersal distance of an animal and its tendency to return to a stationary site. To our knowledge, the homing ability of freshwater turtles and their fidelity is reportedly very low in Asia. We examined mark–recapture data spanning a 4‐year period in Diaoluoshan National Nature Reserve, Hainan Province, China, to investigate the site fidelity and homing behavior of big‐headed turtles Platysternon megacephalum. A total of 11 big‐headed turtles were captured, and all individuals were used in this mark–recapture study. The site fidelity results showed that the adult big‐headed turtles (n = 4) had a 71.43% recapture rate in the original site after their release at the same site, whereas the juveniles (n = 1) showed lower recapture rates (0%). Moreover, the homing behavior results showed that the adults (n = 5) had an 83.33% homing rate after displacement. Adult big‐headed turtles were able to return to their initial capture sites (home) from 150 to 2,400 m away and precisely to their home sites from either upstream or downstream of their capture sites or even from other streams. However, none of the juveniles (n = 4) returned home, despite only being displaced 25–150 m away. These results indicated that the adult big‐headed turtles showed high fidelity to their home site and strong homing ability. In contrast, the juvenile turtles may show an opposite trend but further research is needed.     

Do release-site biases reflect response to the Earth's magnetic field during position determination by homing pigeons?

How homing pigeons (Columba livia) return to their loft from distant, unfamiliar sites has long been a mystery. At many release sites, untreated birds consistently vanish from view in a direction different from the home direction, a phenomenon called the release-site bias. These deviations in flight direction have been implicated in the position determination (or map) step of navigation because they may reflect local distortions in information about location that the birds obtain from the geophysical environment at the release site. Here, we performed a post hoc analysis of the relationship between vanishing bearings and local variations in magnetic intensity using previously published datasets for pigeons homing to lofts in Germany. Vanishing bearings of both experienced and naïve birds were strongly associated with magnetic intensity variations at release sites, with 90 per cent of bearings lying within ±29° of the magnetic intensity slope or contour direction. Our results (i) demonstrate that pigeons respond in an orderly manner to the local structure of the magnetic field at release sites, (ii) provide a mechanism for the occurrence of release-site biases and (iii) suggest that pigeons may derive spatial information from the magnetic field at the release site that could be used to estimate their current position relative to their loft.     

Determination of the absolute visual threshold of a nocturnal seabird, the Common Diving Petrel Pelecanoides urinatrix

Many of the smaller burrowing petrels are active at their colonies during the night. How they find their nesting burrows in the open terrain of an oceanic island or in the even more visually-taxing gloom under a forest canopy (Grubb 1974 and references therein) is a feat which has long intrigued naturalists (Lockley 1942). There is experimental evidence that vision is important in burrow location by the Manx Shearwater Puffinus puffinus (Brooke 1978, James 1986), while olfactory homing by Leach's Petrel Oceanodroma leucorhoa has also been suggested by Grubb (1974).
Additionally it seems likely that a number of petrel species catch a significant fraction of their food at night (Imber 1973, Prince & Francis 1984). Many of the squid presumed to be caught then are not bioluminescent (Imber 1973, Clarke et al. 1981), so their detection presumably demands good night vision. In the context of these observations, the dearth of information on the visual abilities of petrels is remarkable.
The present study investigated the absolute visual threshold of the Common Diving Petrel Pelecanoides urinatrix. Probably because the species is small (c. 130 g) and so vulnerable to predators such as Sub-antarctic Skuas Catharacta antarctica , it is strictly nocturnal at breeding colonies (Thoresen 1969, Payne & Prince 1979). It nests in burrows that are often located under tussock grass Poa spp. Whether the birds catch their crustacean prey (Payne & Prince 1979) by day or night is not known.     

Diving behaviour of white-chinned petrels and its relevance for mitigating longline bycatch

The white-chinned petrel (Procellaria aequinoctialis) is the seabird species most commonly killed by Southern Hemisphere longline fisheries. Despite the importance of diving ability for mitigating longline bycatch, little is known of this species’ diving behaviour. We obtained data from temperature–depth recorders from nine white-chinned petrels breeding on Marion Island, southwestern Indian Ocean, during the late incubation and chick-rearing period. Maximum dive depth (16 m) was slightly deeper than the previous estimate (13 m), but varied considerably among individuals (range 2–16 m). Males dived deeper than females, and birds feeding chicks dived deeper than incubating birds, but dive rate did not differ between the sexes. Time of day had no significant effect on dive depth or rate. Our findings will help to improve the design and performance of mitigation measures aimed at reducing seabird bycatch in longline fisheries, such as the calculation of minimum line sink rates and optimum aerial coverage of bird-scaring lines.     

Mechanisms of visually mediated site recognition by the homing pigeon

The recognition of familiar areas by homing pigeons, Columba livia, is now known to depend at least in part on visual cues. Birds allowed a 5-min preview of the surrounding landscape prior to release home faster than those denied access to such cues, suggesting that recognition is visually mediated. We examined this phenomenon further by asking how memory generated through prior experience with a site is used in recognition. We provided a group of homing pigeons with training experience in which they viewed, through a single transparent vertical face of an otherwise opaque release box, an approximately 140° segment of the landscape for 5 min before release. Training previews were always given from consistent locations and orientations within a release site. Test releases that followed were used to ascertain whether subsequent site recognition necessitated previewing from this already familiar angle and distance, or whether the skill could be extended to novel, nonoverlapping lateral views of the landscape. The results suggested that homing performance was better after presentation of the view recapitulating that seen during training than after showing a novel alternative view. Pigeons may have been using a template of the arrangement of familiar landmarks around the release site as the cue for recognition. The effect, however, disappeared after repeated training, suggesting that repeated release from a site may allow for more extensive visual survey and the memorization of detailed features of the landscape or the extraction of site-specific general features that aid recognition even when a novel view is presented. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Exploitation of inland-breeding Antarctic petrels by south polar skuas

During the austral summer of 1996/1997 we studied south polar skuas at Svarthamaren, Dronning Maud Land, Antarctica, where the world's largest known colony of Antarctic petrels is found. Our censuses suggested approximately 250 full-grown skuas and 140,000 breeding pairs of petrels were present. During their breeding season, skuas did not visit the open sea at least 200 km from the site; they relied entirely on prey caught and scavenged from the petrel colony. Because the site is so isolated, we asked whether the prey (petrels) had swamped the predators (skuas), or whether there was evidence that predator numbers were limited by the size of the prey population. Particularly at the end of the petrel incubation period, we found a close correspondence between the energy required by adult skuas and their chicks, ascertained from time budget studies, and the rate at which petrel eggs disappeared from the colony. This suggests that, in this closed system, the predator population was limited by the prey population, and that predator swamping was not an advantage that petrels gained by nesting in this remote location. Received: 12 April 1999 / Accepted: 30 June 1999     

The white-chinned petrel (<Emphasis Type="Italic">Procellaria aequinoctialis</Emphasis>) on South Georgia: population size,distribution and global significance

More white-chinned petrels (Procellaria aequinoctialis) are accidentally killed in fisheries than probably any other seabird in the world, but the population impact of this mortality is poorly understood, partly because there have been no recent estimates of the species’ abundance. The breeding aggregation on the sub-Antarctic island of South Georgia is believed to be larger than all others combined. We estimated the size of this population by calculating the area of suitable habitat and the density of occupied burrows within it. Some 670,000 occupied nests were estimated for the island at mid-incubation, representing 0.9 million pairs of breeding-age birds associated with South Georgia in the survey seasons (2005/06 and 06/07). This is 40–45% of the previous estimate, but still represents well over half of the global population. If the population is declining due to fishery bycatch, as is likely, the scale of annual mortality in this population alone is at least in the high tens of thousands, and plausibly hundreds of thousands.     

Estimates of population size of white-chinned petrels and grey petrels at Kerguelen Islands and sensitivity to fisheries

White-chinned petrels Procellaria aequinoctialis and grey petrels Procellaria cinerea are among the most frequently killed seabird species by accidental bycatch, and both species have received strong conservation concern. Data on population size are required to evaluate the impact of bycatch and to establish management plans. We estimated the population size of both species at Kerguelen, Southern Indian Ocean, from 2004 to 2006 by explicitly taking into account detection probability of burrows using distance sampling and burrow occupancy. A total of 31 line-transects were distributed across the eastern part of Kerguelen, representing a total length of 566 km. Detectability was low (from 0.19 to 0.54 for white-chinned petrels, 0.58 for grey petrels). Burrow densities varied from 1.37±0.67 to 25.77±5.23 burrows ha⁻¹ for white-chinned petrels and was 2.78±0.79 burrows ha⁻¹ for grey petrels. For white-chinned petrels, these densities were extrapolated to the entire surface area of vegetation and there were 234 000 (186 000–297 000) active burrows on Kerguelen. For grey petrels, the number of active burrows for the eastern part of Kerguelen was 3400 (1900–5600). Based on these estimates, the potential biological removal method suggests that the additional mortality on birds caused by the fisheries operating around Kerguelen can be considered a serious threat for the species at least at the regional scale of the Southern Indian Ocean, especially for grey petrels.     

Chewing lice of Procellaria aequinoctialis Linnaeus, 1758 in Brazil with a new host record

The white-chinned petrel (Procellaria aequinoctialis) is a seabird widely distributed in the circumpolar sub-Antarctic islands and subtropical regions, including Brazilian waters. Among the parasites present on the white-chinned petrel are the chewing lice. This seabird is parasitized by 4 known lice species to date. In this study we evaluated the ectoparasites of 2 white-chinned petrels rescued by an animal rehabilitation center in Rio de Janeiro, Brazil and recorded 4 species of chewing lice, of which 3 are already known for this host. One of the species however, has never been recorded in Brazil and another one has never been recorded parasitizing P. aequinoctialis, making this a new host record.     

Magnetic Navigation

Recent evidence suggests that some amphibians, reptiles and birds may be capable of homing using information about geographic position (“map” information) derived from subtle geographic gradients in the earth's magnetic field. The “magnetic map” hypothesis faces numerous theoretical difficulties, however, due to the extremely high level of sensitivity that would be necessary to detect natural magnetic gradients, and to the presence of spatial irregularities and temporal variation in the geomagnetic field that might make map coordinates derived from magnetic gradients unreliable. To date, the majority of studies carried out to test the magnetic map hypothesis have involved field observations of the effects on homing orientation of naturally occurring spatial or temporal variation in the geomagnetic field. While providing an important first step, these studies are subject to the criticism that the observed changes in homing orientation could result from effects on a magnetic compass, or some other unidentified component of the navigational system, rather than from effects on a magnetic map. The recent development of experimental systems in which navigational ability can be studied under controlled or semi-controlled laboratory conditions has opened up the possibility of using new experimental approaches to more rigorously test the magnetic map hypothesis. After briefly reviewing the available evidence of the geomagnetic field's involvement in the map component of homing, a simple graphical model is presented which describes how the home direction derived from a bicoordinate map varies as a function of the value of one of the map coordinates when the value of the second map coordinate is held constant. In studies of homing orientation in which the value of a specific magnetic field parameter (e.g., total intensity, inclination, etc.) can be varied independently of other putative map parameters, the graphical model can be used to generate qualitative predictions about the changes in the direction of homing orientation that should be observed if the magnetic field parameter being manipulated serves as one coordinate of a bicoordinate map. The relationship between the direction of homing orientation and the value of a putative magnetic map parameter can also be used to generate quantitative predictions about characteristics of the local gradient of that magnetic field parameter in the vicinity of the home site (i.e., the alignment and “home value” of the local gradient) which can then be compared with actual measured values. Together, the qualitative and quantitative predictions of the graphical model permit rigorous tests of whether one or both coordinates of a bicoordinate navigational map are derived from the geomagnetic field.     

Shearwaters sometimes take long homing detours when denied natural outward journey information

The cognitive processes (learning and processing of information) underpinning the long-distance navigation of birds are poorly understood. Here, we used the homing motivation of the Manx shearwater to investigate navigational decision making in a wild bird by displacing them 294 km to the far side of a large island (the island of Ireland). Since shearwaters are reluctant to fly over land, the island blocked the direct route home, forcing a navigational decision. Further still, on the far side of the obstacle, we chose a release site where the use of local knowledge could facilitate a 20% improvement in route efficiency if shearwaters were able to anticipate and avoid a large inlet giving the appearance of open water in the home direction. We found that no shearwater took the most efficient initial route home, but instead oriented in the home direction (even once the obstacle became visible). Upon reaching the obstacle, four shearwaters subsequently circumnavigated the land mass via the long route, travelling a further 900 km as a result. Hence, despite readily orienting homewards immediately after displacement, shearwaters seem unaware of the scale of the obstacle formed by a large land mass despite this being a prominent feature of their regular foraging environment.     

An estimate of population sizes of burrowing seabirds at the Diego Ramirez archipelago, Chile, using distance sampling and burrow-scoping

The Diego Ramirez Islands lie 60 nautical miles southwest of Cape Horn and are the breeding site for three species of burrowing seabirds: blue petrels (Halobaena caerulea), common diving petrels (Pelecanoides urinatrix) and sooty shearwater (Puffinus griseus). Burrowing seabirds are highly vulnerable to predation by introduced vertebrate pests, and Diego Ramirez is an important breeding site because it is one of a few remaining subantarctic island groups with no introduced predators. Diego Ramirez is the only known breeding site for blue petrels in the southeast Pacific region, holding about 80% of the global population of that species, and with a population ten times larger than any other population in the world. We estimated the population size in 2002, using a novel application of the distance sampling technique to determine burrow density, and a burrow-scope with excavations to determine occupying species. We found that density was correlated with slope angle and soil wetness. Burrow densities in flatter terrain with drier soils were 2.03 burrows/m² (95% confidence intervals: 1.82–2.27) and 1.11 burrows/m² (0.84–1.48) in steeper terrain with wetter soils. The occupation rate of burrows were significantly different between habitat types (t=2.74, d.f. 11, P<0.05); in flatter drier habitats the proportion of burrows that led to a nest was 0.85 (0.74–0.96), in steeper wetter habitats this decreased to 0.64 (0.50–0.78). We used a digital elevation model to calculate true area rather than planar area for the two habitat types on the main island of Bartolome, and charts to calculate planar area for the remainder of the archipelago. There were 1.35 (1.15–1.54) million pairs of blue petrels and 99,000 (65,000–134,000) pairs of common diving petrels on the archipelago. These are similar figures to those from the only previous estimate, made in 1980. We found breeding sooty shearwaters for the first time, and estimated a population of several thousand pairs. We emphasise the facility of distance sampling as an unbiased technique with practical advantages over commonly used area search methods for monitoring populations of burrowing seabirds. These advantages include increased survey efficiency allowing a larger sample size for a given effort and a correspondingly tighter estimation of density.     

The use of acoustics to monitor burrow-nesting white-chinned petrels Procellaria aequinoctialis at Bird Island, South Georgia

Tape recordings of two types of vocalisations were used to assess burrow occupancy by white-chinned petrels (Procellaria aequinoctialis) at South Georgia. Birds responded to the rattle call on 74% of occasions and a wheezy call on 85%, with only 10% failing to respond to both calls played one after the other. Occupancy was determined throughout the pre-egg and incubation period and results confirmed what is known about patterns of occupancy by white-chinned petrels. Adults in burrows known to hatch a chick responded on average to 69% of recordings during incubation and less than 10% in only 4% of burrows. Significant inter-site and inter-annual variations in occupancy were recorded, suggesting that this method is sensitive to changes in the number of petrels returning to breed. A sampling protocol for providing population indices for monitoring purposes is recommended. Accepted: 6 March 2000     

Spatial heterogeneity in size and parasitism: How it arises in an estuarine snail population

Populations of Ilyanassa obsoleta, a snail abundant in estuaries along the Atlantic coast of North America, exhibit much unobvious spatial heterogeneity. Lifetime dispersal of snails stands to be great, as they live for decades and can make daily moves of tens of meters. They could distribute uniformly, but in many populations there are characteristic spatial distributions of differently sized and trematode-infected snails. This is the case where this work was done in the Savages Ditch habitat of Rehoboth Bay, Delaware, U.S.A.. The study was designed to explain how the spatial heterogeneity in that habitat arises as a consequence of snail movements. Individually marked snails were tested for trematode infections and released from five well-separated positions. Snails released from each position were in three groups: (1) natives, collected from the position area, and (2) large and (3) small “outlanders”, collected from a site in the habitat that was separated from all release positions, had enhanced tidal currents, and where both size classes were available. Locations of found, released snails were noted for up to four years. Depending on collection site, many native snails were parasitized. In any case, they always tended to disperse in the vicinity where initially collected. Large outlanders (∼ 21% infected) dispersed variably, moving back toward their source area from certain release positions, but not from others. Small outlanders (∼ 4% infected), almost regardless of where released, tended to disperse back toward their source area. Dispersals of these snail groups from the five release positions explains much about how the pattern of spatial heterogeneity seen in the habitat arises.     

Causes of homing behaviour in a group living reef fish

Homing is a common feature in fish, where for instance many freshwater species return to their place of birth to reproduce. Homing in marine species is, however, less understood. Such homing behaviour may be explained by fitness advantages from staying in a known physical environment as well as a known social environment. Cardinalfish of the family of Apogonidae are small, schooling fish, common in shallow waters in temperate and tropical seas. They form apparently stable group structures both in space and time and it has been shown that they may return to their home site after being experimentally removed up to several kilometres. In order to disentangle whether this homing behaviour in one such cardinalfish species, the Banggai cardinalfish, is driven by preference for the home locality or their original social group, I performed a two part field experiment. Firstly, individuals were allowed to choose between known individuals from their original group and unknown individuals from another group. Secondly, individuals were allowed to choose between their original location inhabited by unknown individuals from another group, and a new location inhabited by individuals from their original group. I discuss the evolution of homing behaviours in fish in light of these experiments.     

Avian orientation: effects of cue-conflict experiments with young migratory songbirds in the high Arctic

The migratory orientation of juvenile white-crowned sparrows, Zonotrichia leucophrys gambelli, was investigated by orientation cage experiments in manipulated magnetic fields performed during the evening twilight period in northwestern Canada in autumn. We did the experiments under natural clear skies in three magnetic treatments: (1) in the local geomagnetic field; (2) in a deflected magnetic field (mN shifted −90°); and (3) after exposure to a deflected magnetic field (mN −90°) for 1 h before the cage experiment performed in the local geomagnetic field at dusk. Subjects showed a mean orientation towards geographical east in the local geomagnetic field, north of the expected migratory direction towards southeast. The sparrows responded consistently to the shifted magnetic field, demonstrating the use of a magnetic compass during their first autumn migration. Birds exposed to a cue conflict for 1 h on the same day before the experiment, and tested in the local geomagnetic field at sunset, showed the same northerly orientation as birds exposed to a shifted magnetic field during the experiment. This result indicates that information transfer occurred between magnetic and celestial cues. Thus, the birds' orientation shifted relative to available sunset and geomagnetic cues during the experimental hour. The mean orientation of birds exposed to deflected magnetic fields prior to and during testing was recorded up to two more times in the local geomagnetic field under natural clear and overcast skies before release, resulting in scattered mean orientations.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

Homing by path integration in a new environment

Path integration was tested in golden hamsters, Mesocricetus auratus, within a new environment and in darkness. From the exit of its home cage, the subject was lured over a certain distance into the experimental arena, and then startled by a sudden noise to induce instantaneous homing. The subjects in experiment 1 had previously been tested within an identical arena in another building; they started the outward journey from a peripheral nest. Upon hearing the sound, all subjects returned in the correct direction to the arena border. In experiments 2 and 3, experimentally na?ve subjects started the outward trip from a central nest exit. Both groups initially oriented correctly, but only a few of subjects returned to the nest. According to computational considerations, experiment 1 required mainly the calculation of the homing direction, while experiments 2 and 3 required a homing vector. Furthermore, the experienced subjects may have been helped by their homing experience in the same type of arena, while the na?ve subjects may not have ‘trusted’ self-generated vector information sufficiently to follow it to the goal in an uncharted environment. Thus, the performance, but not the computation of self-generated vector information, may depend on the animal's experience. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Factors affecting the number and mortality of seabirds attending trawlers and long-liners in the Kerguelen area

The factors affecting the number and the mortality rates of seabirds attending long-liners and trawlers fishing in the Kerguelen area were studied during four successive seasons (1994–1997), based on observations carried out onboard by dedicated observers. Twenty-four species of seabirds were observed attending fishing vessels, representing an average of 591 birds/census. The total numbers attending varied mainly according to the year, the cloud cover and the presence of offal from long-liners. The dumping of offal increased the numbers of birds attending the vessel, especially when the offal could be easily handled by birds. The activity of the vessels also affected the numbers attending, birds being more abundant during line setting and trawl hauling. White-chinned petrels were the most abundant ship-following seabirds, followed by black-browed albatrosses, giant petrels and cape petrels. The number of white-chinned petrels, black-browed and grey-headed albatrosses attending fishing vessels increased in the time between spring and autumn, whereas it was the reverse situation for giant petrels and cape petrels. Four species of seabirds were caught by fishing gear, mainly by long-lines: white-chinned petrels, and black-browed, grey-headed and wandering albatrosses. Taking into account the number of birds from each species attending long-liners and known to be potential by-catch, some species appear to be more susceptible to being caught than others. White-chinned and grey-headed albatrosses are caught in much higher proportions than the numbers present, whereas black-browed albatrosses are caught in lower numbers. Giant petrels are abundant around long-liners but were never caught. In long-liners, most birds were killed when the lines were set during the day or when the deployment of the scaring device was not successful, with an overall figure of 0.47 birds/1000 hooks. Only one albatross was caught when the lines were set during the night. White-chinned petrels represented 92.2% of all birds killed by long-liners. The number of birds caught varied significantly among months and among years. The type of bait used also affected the catch rate. The catch rate was related to the number of birds attending the long-liner only for black-browed albatrosses. Most birds killed by trawlers were entangled by the netsonde cable. The efficiency of mitigation measures in order to reduce seabird mortality is discussed and it is stressed that night setting is the most efficient way to reduce mortality and should be enforced everywhere when possible. However, further methods should be developed to reduce the mortality of species active at night, especially white-chinned petrels whose populations in the Indian Ocean may by threatened by long-line fisheries. Accepted: 15 October 1999