Pachyptila Desolata Research Articles

Patterns of recovery in extant and extirpated seabirds after the world's largest multipredator eradication.

Eradicating invasive predators from islands can result in substantial recovery of seabirds, but the mechanisms that drive population changes remain poorly understood. Meta-analyses have recently revealed that immigration is surprisingly important to the recovery of philopatric seabirds, but it is not known whether dispersal and philopatry interact predictably to determine rates of population growth and changes of distribution. We used whole-island surveys and long-term monitoring plots to study the abundance, distribution, and trends of 4 burrowing seabird species on Macquarie Island, Australia, to examine the legacy impacts of invasive species and ongoing responses to the world's largest eradication of multiple species of vertebrates. Wekas (Gallirallus australis) were eradicated in 1988; cats (Felis catus) in 2001; and rabbits (Oryctolagus cuniculus), black rats (Rattus rattus), and mice (Mus mus) in 2011-2014. We compared surveys from 1976-1979 and 2017-2018 and monitoring from the 1990s and 2000s onward. Antarctic prions (Pachyptila desolata) and white-headed petrels (Pterodroma lessonii) increased ∼1% per year. Blue petrels (Halobaena caerulea) and gray petrels (Procellaria cinerea) recolonized following extirpation from the main island in the 1900s but remained spatially and numerically rare in 2018. However, they increased rapidly at 14% and 10% per year, respectively, since cat eradication in 2001. Blue and gray petrel recolonization occurred on steep, dry, west-facing slopes close to ridgelines at low elevation (i.e., high-quality petrel habitat). They overlapped <5% with the distribution of Antarctic prion and white-headed petrels whichoccurred in suboptimal shallow, wet, east-facing slopes at high elevation. We inferred that the speed of population growth of recolonizing species was related to their numerically smaller starting size compared with the established species and was driven by immigration and selection of ideal habitat.

Mitochondrial DNA structuring of Antarctic prions (Pachyptila desolata, Procellariidae)

Prions (Pachyptila) are small seabirds with a Southern Hemisphere breeding distribution. Antarctic prion (Pachyptila desolata) and Salvin’s prion (P. salvini) are two species that are regularly recorded in New Zealand as beach-wrecks but they are difficult to distinguish morphologically. Salvin’s prion is restricted to breeding on the Prince Edward Islands and Crozet Islands in the Indian Ocean but Antarctic prions have a circumpolar breeding distribution on numerous sub-Antarctic and Antarctic islands in the Southern, South Atlantic and Indian Oceans. Our aim was to examine the level of mitochondrial DNA (mtDNA) structuring within Antarctic prion and Salvin’s prion colonies, to test whether this technique can determine the provenance of beach-cast birds. The Auckland Islands Antarctic prion population exhibited distinct mtDNA haplotypes from all other populations, supporting the suggestion that these islands may have been an ice-free refugium during the Last Glacial Maximum. All other sampled breeding populations shared haplotypes, limiting the use of these sequences for determining the provenance of beach-cast birds. None of our museum specimens of Salvin’s prion collected from breeding colonies produced DNA sequences. This result indicates that the method by which these specimens, which were collected in the 1960s and 70s, were preserved, or subsequent treatments, has resulted in the loss of their DNA.

Variation Among Species and Populations, and Carry-Over Effects of Winter Exposure on Mercury Accumulation in Small Petrels

Even in areas as remote as the Southern Ocean, marine organisms are exposed to contaminants that arrive through long-range atmospheric transport, such as mercury (Hg), a highly toxic metal. In previous studies in the Southern Ocean, inter-specific differences in Hg contamination in seabirds was generally related to their distribution and trophic position. However, the Blue Petrel (Halobaena caerulea) was a notable exception among small seabirds, with higher Hg levels than expected. In this study, we compared the Hg contamination of Blue Petrels and Thin-billed Prions (Pachyptila belcheri), which both spend the non-breeding season in polar waters, with that of Antarctic Prions (Pachyptila desolata), which spend the winter in subtropical waters. We collected body feathers and blood samples, representing exposure during different time-frames. Hg concentrations in feathers, which reflect contamination throughout the annual cycle, were related to δ13C values, and varied with ocean basin and species. Blue Petrels from breeding colonies in the southeast Pacific Ocean had much higher feather Hg concentrations than expected after accounting for latitude and their low trophic positions. Both Hg concentrations and δ15N in blood samples of Blue Petrels were much lower at the end than at the start of the breeding period, indicating a marked decline in Hg contamination and trophic positions, and the carry-over of Hg burdens between the wintering and breeding periods. Elevated Hg levels may reflect greater reliance on myctophids or foraging in sea-ice environments. Our study underlines that carry-over of Hg concentrations in prey consumed in winter may determine body Hg burdens well into the breeding season.

Generating unbiased estimates of burrowing seabird populations

Maximising survey efficiency can help reduce the tradeoff between spending limited conservation resources on identifying population changes and responding to those changes through management. Burrow‐nesting seabirds are particularly challenging to survey because nests cannot be counted directly. We evaluated a stratified random survey design for generating unbiased population estimates simultaneously for four petrel species nesting on Macquarie Island, Australia, where the survey cue, burrow entrances, is similar for all species. We also compared the use of design‐based and model‐based analyses for minimising uncertainty in estimates. We recorded 2845 Antarctic prion burrows, 306 white‐headed petrel burrows and two blue petrel burrows while distance‐sampling along 154 km of transects. For blue petrels and grey petrels, we completed nocturnal searches along a further 71 km and searched 249 km of tracks during follow‐up ground searches. We failed to generate unbiased population estimates for two rare and localised species, blue and grey petrels, from our stratified random survey. Only for the most widespread and abundant species, Antarctic prion, did the estimate have reasonable power to detect a rapid population change. Model‐based analyses of the stratified random survey data did not improve upon traditional design‐based analyses in terms of uncertainty in population estimates, but they did provide useful spatial representation of current populations. Models that used the targeted survey data did not reflect current population sizes and distributions of the two rare and localised species. We found that when species ecologies, distributions and abundances vary, a multi‐method approach to surveys is needed. Species with low abundance that occur patchily across large islands are likely to be best estimated using targeted surveys, whereas widespread and abundant species can be accurately and precisely estimated from randomised surveys using informative model‐based analyses.

Variation among species and populations in bill shape and size in three planktivorous petrels

Morphological variation in biological structures may be driven by genetic and environmental factors, such as inter- and intraspecific competition for resources. In seabirds, although the bill is also involved in vocalization, olfaction, sexual selection and defence, the main drivers of high morphological plasticity in bill size and shape appear to relate primarily to diet and thus to niche differentiation. Here, we combined geometric morphometrics and comparisons of linear measurements as a precise tool for measuring shape variation in anatomical features, to investigate the differences among species and populations (island groups) in bill shape of three planktivorous petrels (Antarctic prion Pachyptila desolata, blue petrel Halobaena caerulea and thin-billed prion Pachyptila belcheri). Fieldwork was carried out in South Georgia (54° 0′ S, 38° 3′ W), Falkland (51° 42′ S, 57° 51′ W), Diego Ramírez (56° 31′ S, 68° 44′ W) and Kerguelen (49° 20′ S, 69° 20′ E) Islands, from 2010 to 2021. Results show that the bills of Antarctic prions were more robust and shorter, appropriate for filtering large amounts of small prey. Blue petrels and thin-billed prions had narrower and longer bills, effective for catching and tearing large single prey. Also, Antarctic prions and blue petrels from Kerguelen had longer and narrower bills than conspecifics from other colonies, which could potentially be explained by geographic variation in diet. In conclusion, prey availability and diversity appear to be important factors influencing variation in bill morphology. This study highlights the utility of geometric morphometrics for investigating bill shape variation in seabirds. Nevertheless, further studies are needed to better understand selective pressures leading to morphological variation of biological structures.

Independent evolution of intermediate bill widths in a seabird clade

Interspecific introgression can occur between species that evolve rapidly within an adaptive radiation. Pachyptila petrels differ in bill size and are characterised by incomplete reproductive isolation, leading to interspecific gene flow. Salvin’s prion (Pachyptila salvini), whose bill width is intermediate between broad-billed (P. vittata) and Antarctic (P. desolata) prions, evolved through homoploid hybrid speciation. MacGillivray’s prion (P. macgillivrayi), known from a single population on St Paul (Indian Ocean), has a bill width intermediate between salvini and vittata and could also be the product of interspecies introgression or hybrid speciation. Recently, another prion population phenotypically similar to macgillivrayi was discovered on Gough (Atlantic Ocean), where it breeds 3 months later than vittata. The similarity in bill width between the medium-billed birds on Gough and macgillivrayi suggest that they could be closely related. In this study, we used genetic and morphological data to infer the phylogenetic position and evolutionary history of P. macgillivrayi and the Gough medium-billed prion relative other Pachyptila taxa, to determine whether species with medium bill widths evolved through common ancestry or convergence. We found that Gough medium-billed prions belong to the same evolutionary lineage as macgillivrayi, representing a new population of MacGillivray’s prion that originated through a colonisation event from St Paul. We show that macgillivrayi’s medium bill width evolved through divergence (genetic drift) and independently from that of salvini, which evolved through hybridisation (gene flow). This represents the independent convergence towards a similarly medium-billed phenotype. The newly discovered MacGillivray’s prion population on Gough is of utmost conservation relevance, as the relict macgillivrayi population in the Indian Ocean is very small.

Contextual variations in calls of two nonoscine birds: the blue petrel Halobaena caerulea and the Antarctic prion Pachyptila desolata

Abstract Bird vocalizations are critical cues in social interactions as they convey temporary information varying with the social context, for example, the signaler motivation when facing a rival or a potential mate. To date, literature mainly focused on learning birds. Burrowing petrels (Procellariidae) are nonlearning birds with a limited vocal repertoire. Bachelor males communicate with conspecifics with a single call emitted in three situations: in the absence of a certain auditory (spontaneous calls), toward females (female-directed calls), and toward males (male-directed calls). We first hypothesized that, although the call structure is preserved, temporal and spectral parameters vary between the three call types of bachelor males, translating different motivations (Motivation Hypothesis). To go further, we hypothesized that acoustic variations in male-directed calls indicate the signaler’s aggressive motivation and, therefore, the variations are similar whether calls are produced by breeder or bachelor males (Breeding Status Hypothesis). We tested the two hypotheses performing field playback experiments on two petrel species: the blue petrel (Halobaena caerulea) and the Antarctic prion (Pachyptila desolata). Despite the obvious call stereotypy, we observed temporal variations and frequency shifts when males react to a female or a male, which may translate the sexual or aggressive motivation of the signaler. Furthermore, the similarity of variations in male-directed calls of both breeder and bachelor males suggests the aggressive motivation. So far, vocal plasticity in nonlearning birds has been greatly underestimated. Here, we highlighted the expression of different motivations through vocal variations and the ability to produce frequency variations in species with genetically coded vocalizations.

Mercury isotopes of key tissues document mercury metabolic processes in seabirds

Seabirds accumulate significant amounts of mercury (Hg) due to their long-life span together with their medium to high trophic position in marine food webs. Hg speciation and Hg isotopic analyses of total Hg in different tissues (pectoral muscles, liver, brain, kidneys, blood and feathers) were assessed to investigate their detoxification mechanisms. Three species with contrasted ecological characteristics were studied: the Antarctic prion (zooplankton feeder), the white-chinned petrel (pelagic generalist consumer) and the southern giant petrel (scavenger on seabirds and marine mammals). The difference of mass-dependent fractionation (MDF, δ202Hg) values between liver and muscles (up to 0.94 ‰) in all three seabirds strongly suggests hepatic demethylation of the isotopically lighter methylmercury (MeHg) and subsequent redistribution of the isotopically heavier fraction of MeHg towards the muscles. Similarly, higher δ202Hg values in feathers (up to 1.88 ‰) relative to muscles and higher proportion of MeHg in feathers (94–97%) than muscles (30–70%) likely indicate potential MeHg demethylation in muscle and preferential excretion of MeHg (isotopically heavier) in the growing feathers during moult. The extents of these key detoxification processes were strongly dependent on the species-specific detoxification strategies and levels of dietary MeHg exposure. We also found higher mass-independent fractionation (MIF, Δ199Hg) values in feathers relative to internal tissues, possibly due to different integration times of Hg exposure between permanently active organs and inert tissues as feathers. Hg isotope variations reported in this study show evidence of detoxification processes in seabirds and propose a powerful approach for deep investigation of the Hg metabolic processes in seabirds.

Niche switching and leapfrog foraging: movement ecology of sympatric petrels during the early breeding season

BackgroundThe timing of events in the early part of the breeding season is crucially important for successful reproduction. Long-lived animals that migrate large distances independently of each other meet at the breeding sites to re-establish their pair bonds and coordinate their breeding duties with their partners.MethodsUsing miniature light-geolocation and immersion data together with blood stable isotopes, we studied the early breeding season in Thin-billed prions Pachyptila belcheri, Antarctic prions P. desolata and Blue petrels Halobaena caerulea breeding at Kerguelen Islands in the Indian Ocean. These three species exhibit differences in their winter habitat and timing of migration, moult and breeding. We hypothesised that these differences would influence their behaviour during the early breeding season.ResultsIn line with our hypothesis, we found clear differences not only in the timing of colony attendance, but also in the time budgets while at sea and in habitat use. Both early breeding Blue petrels and late breeding Antarctic prions spent about 8 h per day in flight and 15 h foraging. In comparison, Thin-billed prions, which breed in mid-summer, spent less time (5 h daily) in flight and more time (18 h daily) foraging, thus maximizing the time spent foraging during the longest daylight days of the year. While the ecological habitat parameters (sea temperature, wind, productivity) of Thin-billed prions and Blue petrels were relatively stable throughout the year, Antarctic prions showed clear niche switching, caused by leapfrogging between the northernmost winter distribution to the southernmost distribution during the early breeding season. Blood stable isotopes confirmed the habitat switch between the inter-breeding and early breeding periods and highlighted trophic segregation with Blue petrels feeding more on fish and Antarctic petrels more on crustaceans during the early breeding period.ConclusionWe found that the three sympatric petrel species segregated in time and space, both in the winter and the early breeding season. The interplay of timing and distribution meant that the three species show the full range of migratory strategies, from niche-tracking Blue petrels to niche-switching Antarctic prions. The latitudinal distribution resembled the leapfrogging of terrestrial avian migrant species or populations.

Males’ calls carry information about individual identity and morphological characteristics of the caller in burrowing petrels

Acoustic communication in burrowing petrels has been poorly studied. However, as for many other bird species, acoustic communication seems to play an essential role in social interactions during the breeding season of these seabirds. Bachelor males call from their burrow, likely to attract females, but also when vocally challenged by other males. Calling in the breeding colony exposes petrels to high predation risks and thus it should provide an important benefit. The present study focuses on the informative content of males’ calls in the blue petrel Halobaena caerulea and the Antarctic prion Pachyptila desolata, two monogamous petrel species producing a single egg per year. We tested the hypotheses that acoustic parameters of a male's calls 1) reflect phenotypic characteristics, and 2) bear an individual vocal signature. To do so, we first tested on both species the relationships between seven morphometric measurements and 11 acoustic parameters using multivariate analyses. Second, we performed a between‐class analysis and calculated the potential of individuality coding (i.e. the ratio between intra‐ and inter‐individual variabilities) for acoustic parameters in both spectral and temporal domains. Results show acoustic parameters (especially energy quartiles, call duration, and syllable or phrase rate) reflect the caller's body size, bill morphology and wing morphology in both species. Considering the seeming pertinence of wing morphology, we suggest wing area may be a more relevant trait to consider than wing length when studying soaring birds. The results support the idea that energy quartiles, phrase rate and call duration also code for individual identity. Information carried by males’ calls might play a role in social interactions, such as burrow defence (e.g. male‐male competition, neighbour‐stranger discrimination) and/or female mate choice.

Additive Traits Lead to Feeding Advantage and Reproductive Isolation, Promoting Homoploid Hybrid Speciation.

Speciation through homoploid hybridization (HHS) is considered extremely rare in animals. This is mainly because the establishment of reproductive isolation as a product of hybridization is uncommon. Additionally, many traits are underpinned by polygeny and/or incomplete dominance, where the hybrid phenotype is an additive blend of parental characteristics. Phenotypically intermediate hybrids are usually at a fitness disadvantage compared with parental species and tend to vanish through backcrossing with parental population(s). It is therefore unknown whether the additive nature of hybrid traits in itself could lead successfully to HHS. Using a multi-marker genetic data set and a meta-analysis of diet and morphology, we investigated a potential case of HHS in the prions (Pachyptila spp.), seabirds distinguished by their bills, prey choice, and timing of breeding. Using approximate Bayesian computation, we show that the medium-billed Salvin’s prion (Pachyptila salvini) could be a hybrid between the narrow-billed Antarctic prion (Pachyptila desolata) and broad-billed prion (Pachyptila vittata). Remarkably, P. salvini’s intermediate bill width has given it a feeding advantage with respect to the other Pachyptila species, allowing it to consume a broader range of prey, potentially increasing its fitness. Available metadata showed that P. salvini is also intermediate in breeding phenology and, with no overlap in breeding times, it is effectively reproductively isolated from either parental species through allochrony. These results provide evidence for a case of HHS in nature, and show for the first time that additivity of divergent parental traits alone can lead directly to increased hybrid fitness and reproductive isolation.

Geometric morphometrics reveal interspecific and sexual differences in bill morphology in four sympatric planktivorous petrels

AbstractVariation in morphological structures may indicate the existence of ecological differences between species or sexes. In birds, the bill is one of the structures most affected by selection pressures because it is directly involved with several biological functions, particularly the acquisition of food. In this study, we combined geometric morphometrics and comparisons of linear measurements to assess the presence of sexual dimorphism and differences in bill shape and size of four species of abundant zooplanktivorous seabirds that coexist during their breeding season in Southern Ocean ecosystems [blue petrel (Halobaena caerulea), Antarctic prion (Pachyptila desolata), common diving petrel (Pelecanoides urinatrix) and South Georgia diving petrel (P. georgicus)]. The results showed that bills of Antarctic prion and blue petrel differed noticeably in size and shape from those of the two diving petrels, whereas those of common diving and South Georgian diving petrels overlapped in bill shape. These differences may be due to diet segregation or factors such as diving strategy, vocalizations or olfactory development. In addition, there was sexual dimorphism in bill shape or size in all four species. However, we could not directly attribute these differences to selection pressures because of the lack of studies comparing feeding ecology between sexes in these seabirds. These results reveal relationships between the bill shape and key factors of the ecology of these species, and demonstrate the usefulness of geometric morphometrics for detecting interspecific and sexual differences in species of otherwise sexually monomorphic petrels.

Does genetic structure reflect differences in non-breeding movements? A case study in small, highly mobile seabirds

BackgroundIn seabirds, the extent of population genetic and phylogeographic structure varies extensively among species. Genetic structure is lacking in some species, but present in others despite the absence of obvious physical barriers (landmarks), suggesting that other mechanisms restrict gene flow. It has been proposed that the extent of genetic structure in seabirds is best explained by relative overlap in non-breeding distributions of birds from different populations. We used results from the analysis of microsatellite DNA variation and geolocation (tracking) data to test this hypothesis. We studied three small (130–200 g), very abundant, zooplanktivorous petrels (Procellariiformes, Aves), each sampled at two breeding populations that were widely separated (Atlantic and Indian Ocean sectors of the Southern Ocean) but differed in the degree of overlap in non-breeding distributions; the wintering areas of the two Antarctic prion (Pachyptila desolata) populations are separated by over 5000 km, whereas those of the blue petrels (Halobaena caerulea) and thin-billed prions (P. belcheri) show considerable overlap. Therefore, we expected the breeding populations of blue petrels and thin-billed prions to show high connectivity despite their geographical distance, and those of Antarctic prions to be genetically differentiated.ResultsMicrosatellite (at 18 loci) and cytochrome b sequence data suggested a lack of genetic structure in all three species. We thus found no relationship between genetic and spatial structure (relative overlap in non-breeding distributions) in these pelagic seabirds.ConclusionsIn line with other Southern Ocean taxa, geographic distance did not lead to genetic differences between widely spaced populations of Southern Ocean petrel species.

Contrasting migratory responses of two closely related seabirds to long-term climate change

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 559:231-242 (2016) - DOI: https://doi.org/10.3354/meps11875 Contrasting migratory responses of two closely related seabirds to long-term climate change W. James Grecian1,*, Graeme A. Taylor2, Graeme Loh3, Rona A. R. McGill4, Colin M. Miskelly5, Richard A. Phillips6, David R. Thompson7, Robert W. Furness1 1Institute of Biodiversity, Animal Health & Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK 2Department of Conservation, PO Box 10420, Wellington 6143, New Zealand 3Department of Conservation, PO Box 5244, Dunedin 9058, New Zealand 4NERC Life Sciences Mass Spectrometry Facility, Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride G75 0QF, UK 5Museum of New Zealand Te Papa Tongarewa, PO Box 467, Wellington 6140, New Zealand 6British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK 7National Institute of Water and Atmospheric Research Ltd, Kilbirnie, Wellington 6021, New Zealand *Corresponding author: james.grecian@glasgow.ac.uk ABSTRACT: Many marine predators migrate between breeding and non-breeding areas to target resources that are seasonal but spatio-temporally predictable, and so are vulnerable to climate-induced changes in prey phenology and abundance. In the Southern Ocean, small petrels are major consumers, but perturbations in the ecosystem through ocean warming are altering food-web structure and have been linked to poleward shifts in the distribution of their cold-water zooplankton prey. In this study, we focused on 2 small congeneric petrels: the broad-billed prion Pachyptila vittata and the Antarctic prion P. desolata. Both are planktivorous, but the broad-billed prion specialises in feeding on large copepods. We investigated historical trends in non-breeding distribution by analysing feather stable isotope ratios from a time-series dating back to 1926, and examined contemporary non-breeding distributions of broad-billed prions tracked using miniaturised geolocation-immersion loggers. After controlling temporally for the Suess effect, we found that the δ13C signatures of Antarctic prions, but not broad-billed prions, declined during the study period. This suggests a southward shift in Antarctic prion non-breeding distribution over the last century. Both species exhibited significant declines in δ15N during the same period, indicative of long-term decreases in marine productivity in their moulting areas, or changes in the trophic structure of prey communities. Tracked broad-billed prions migrated ca. 1000 km to an area east of the breeding colony where the Louisville seamount chain bisects the subtropical front. Topographically driven upwellings are stable and predictable features and may be crucial in aggregating plankton. Targeting seamounts could therefore mitigate the impact of climate-induced prey shifts by providing refugia for the broad-billed prion. KEY WORDS: Biologging · Conservation · Migration · Moult · Movement · Non-breeding behaviour · Seamounts · Stable isotopes · Upwelling zones Full text in pdf format PreviousNextCite this article as: Grecian WJ, Taylor GA, Loh G, McGill RAR and others (2016) Contrasting migratory responses of two closely related seabirds to long-term climate change. Mar Ecol Prog Ser 559:231-242. https://doi.org/10.3354/meps11875 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 559. Online publication date: November 09, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Combination of At-Sea Activity, Geolocation and Feather Stable Isotopes Documents Where and When Seabirds Molt

Key facets of the foraging ecology of seabirds during the inter-breeding period still remain poorly understood because of the difficulty of studying them at sea, including during the energy-demanding moulting stage. Here, the extent to which three sympatric petrels (Antarctic and thin-billed prions, and blue petrel) from the subantarctic Kerguelen Islands modify their foraging ecology during moult was investigated using a combination of complementary tools, namely miniaturized saltwater immersion geolocators (GLS) and the isotopic method. Firstly, moulting behaviour was first characterized in the blue petrel, a reference species that is known to renew its plumage in autumn. GLS and feather stable isotopes (13C as a proxy of the birds’ foraging habitat) indicated that the post-breeding moult of blue petrel occurred in Antarctic waters. Importantly, activity recorders showed that moult was marked by a strong peak in time spent daily sitting on water, which thereafter declined to lower values during the remaining winter months. Secondly, the peak in time spent sitting on water was used as a proxy to characterize the contrasted moult strategies of the two prion species. As blue petrels demonstrated, thin-billed prions moulted during the post-breeding period in cold Antarctic waters where they fed primarily on low trophic level prey, most likely Antarctic krill (15N as a proxy of the birds’ diet). By contrast, Antarctic prions presented an unexpected pre-breeding moult of longer duration that took place further north, in warm subtropical waters. Interestingly, the two Antarctic moulting species, the blue petrel and thin-billed prion, renewed their plumage at the same time and within the same oceanic zone that is likely to be a previously undescribed hot spot of seabird diversity during the Austral autumn. The study contributes to a growing body of evidence that closely-related species exhibit various foraging strategies allowing ecological segregation and sheds new light on the poorly known critical moulting stage of seabirds.

Wide range of metallic and organic contaminants in various tissues of the Antarctic prion, a planktonophagous seabird from the Southern Ocean

Trace elements (n=14) and persistent organic pollutants (POPs, n=30) were measured in blood, liver, kidney, muscle and feathers of 10 Antarctic prions (Pachyptila desolata) from Kerguelen Islands, southern Indian Ocean, in order to assess their concentrations, tissue distribution, and inter-tissue and inter-contaminant relationships. Liver, kidney and feathers presented the highest burdens of arsenic, cadmium and mercury, respectively. Concentrations of cadmium, copper, iron, and zinc correlated in liver and muscle, suggesting that uptake and pathways of metabolism and storage were similar for these elements. The major POPs were 4,4'-DDE, mirex, PCB-153 and PCB-138. The concentrations and tissue distribution patterns of environmental contaminants were overall in accordance with previous results in other seabirds. Conversely, some Antarctic prions showed surprisingly high concentrations of BDE-209. This compound has been rarely observed in seabirds before, and its presence in Antarctic prions could be due to the species feeding habits or to the ingestion of plastic debris. Overall, the study shows that relatively lower trophic level seabirds (zooplankton-eaters) breeding in the remote southern Indian Ocean are exposed to a wide range of environmental contaminants, in particular cadmium, selenium and some emerging-POPs, which merits further toxicological investigations.

Cool, cold or colder? Spatial segregation of prions and blue petrels is explained by differences in preferred sea surface temperatures.

The Southern Ocean provides one of the largest environmental gradients on Earth that lacks geographical barriers, and small but highly mobile petrels living there may offer fine models of evolution of diversity along environmental gradients. Using geolocation devices, we investigated the winter distribution of closely related petrel species breeding sympatrically in the southern Indian Ocean, and applied ecological niche models to compare environmental conditions in the habitat used. We show that thin-billed prions (Pachyptila belcheri), Antarctic prions (Pachyptila desolata) and blue petrels (Halobaena caerulea) from the Kerguelen archipelago in the southern Indian Ocean segregate latitudinally, sea surface temperature being the most important variable separating the distribution of the species. Antarctic prions spent the winter north of the Polar Front in temperate waters, whereas blue petrels were found south of the Polar Front in Antarctic waters. Thin-billed prions preferred intermediate latitudes and temperatures. Stable isotope values of feathers reflected this near complete niche separation across an ecological gradient that spans large scales, and suggest evolutionary isolation by environment. In pelagic seabirds that exploit large areas of ocean, spatial niche partitioning may not only facilitate coexistence among ecologically similar species, but may also have driven their evolution in the absence of geographical barriers.

Quantifying variation in δ 13C and δ 15N isotopes within and between feathers and individuals: Is one sample enough?

Studies of avian migration increasingly use stable isotope analysis to provide vital trophic and spatial markers. However, when interpreting differences in stable isotope values of feathers, many studies are forced to make assumptions about the timing of moult. A fundamental question remains about the consistency of these values within and between feathers from the same individual. In this study, we examine variation in carbon and nitrogen isotopes by sub-sampling feathers collected from the wings of adults of two small congeneric petrel species, the broad-billed Pachyptila vittata and Antarctic prion P. desolata. Broad-billed prion feather vane material was enriched in 15N compared to feather rachis material, but there was no detectable difference in δ 13C. Comparison of multiple samples taken from Antarctic prion feathers indicated subtle difference in isotopes; rachis material was enriched in 13C compared to vane material, and there were differences along the length of the feather, with samples from the middle and tip of the feather depleted in 15N compared to those from the base. While the greatest proportion of model variance was explained by differences between feathers and individuals, the magnitude of these within-feather differences was up to 0.5 ‰ in δ 15N and 0.8 ‰ in δ 13C. We discuss the potential drivers of these differences, linking isotopic variation to individual-level dietary differences, movement patterns and temporal dietary shifts. A novel result is that within-feather differences in δ 13C may be attributed to differences in keratin structure within feathers, suggesting further work is required to understand the role of different amino acids. Our results highlight the importance of multiple sampling regimes that consider both within- and between-feather variation in studies using stable isotopes. Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-015-2618-8) contains supplementary material, which is available to authorized users.

Moulting patterns drive within-individual variations of stable isotopes and mercury in seabird body feathers: implications for monitoring of the marine environment

One major limitation in the use of body feathers of seabirds as a monitoring tool of the trophic structure and contamination levels of marine ecosystems is the degree of heterogeneity in feather chemical composition within individuals. Here, we tested the hypothesis that moulting patterns drive body feather heterogeneity, with synchronous moult minimizing within-individual variations, in contrast to asynchronous feather growth. Chicks of white-chinned petrels Procellaria aequinoctialis (representative of bird chicks) and adults of king penguins Aptenodytes patagonicus (representative of adult penguins) that moult their body feathers synchronously showed very low within-individual variations in their feather δ13C and δ15N values and mercury (Hg) concentrations. By contrast, body feathers of adults of Antarctic prions Pachyptila desolata (representative of adult seabirds with asynchronous feather growth during a protracted moult) presented much higher within-individual variances for the three parameters. These findings have three important implications for birds presenting a synchronous body moult. (1) They suggest that all body feathers from the same individual have identical δ13C and δ15N values and Hg content. (2) They predict negligible within-individual variations in the body feather values of other useful stable isotopes, such as δ2H and δ34S, as well as in the concentrations of other compounds that are deposited in the keratin structure. (3) Analysis of one or any number of pooled body feathers is equally representative of the individual. In conclusion, we recommend that long-term routine monitoring investigations focus on birds presenting synchronous rather than asynchronous moult of body feathers both in marine and terrestrial environments. This means targeting chicks rather than adults and, for seabirds, penguins rather than adults of flying species.

Ecological Segregation in Space, Time and Trophic Niche of Sympatric Planktivorous Petrels

The principle of competitive exclusion postulates that ecologically-similar species are expected to partition their use of resources, leading to niche divergence. The most likely mechanisms allowing such coexistence are considered to be segregation in a horizontal, vertical or temporal dimension, or, where these overlap, a difference in trophic niche. Here, by combining information obtained from tracking devices (geolocator-immersion and time depth recorders), stable isotope analyses of blood, and conventional morphometry, we provide a detailed investigation of the ecological mechanisms that explain the coexistence of four species of abundant, zooplanktivorous seabirds in Southern Ocean ecosystems (blue petrel Halobaena caerulea, Antarctic prion Pachyptila desolata, common diving petrel Pelecanoides urinatrix and South Georgian diving petrel P. georgicus). The results revealed a combination of horizontal, vertical and temporal foraging segregation during the breeding season. The stable isotope and morphological analyses reinforced this conclusion, indicating that each species occupied a distinct trophic space, and that this appears to reflect adaptations in terms of flight performance. In conclusion, the present study indicated that although there was a degree of overlap in some measures of foraging behaviour, overall the four taxa operated in very different ecological space despite breeding in close proximity. We therefore provide important insight into the mechanisms allowing these very large populations of ecologically-similar predators to coexist.