Antarctic Prions Pachyptila Desolata Research Articles

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.

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.

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.

Mottled Petrel Pterodroma inexpectata in the Drake Passage, South Atlantic, March 2008

The ‘Atlantic Odyssey’ is the annual reposi- tioning trip of the Professor Molchanov, a small Expedition Cruise ship that spends the austral summer in Antarctic waters and the northern summer in the Arctic. For enthusiasts of seabirds, cetaceans, islands, and photography, the voyage from Ushuaia in Argentina south to the Antarctic Peninsula, and thence north to Cape Verde via South Georgia, the Tristan da Cunha group, St Helena, and Ascension Island provides a superb opportunity to view marine life across 70 degrees of latitude. On the morning of 11 March 2008, we were heading south on our second day in the Drake Passage, with a moderate northwest wind, two-metre swell, high thin overcast skies, and excellent visibility. At 11.20 hours (ship’s time, position 60o17’S 69o44’W) we were observing from the sun deck above the bridge when a medium-sized petrel flew close across the bow from east to west. Similar sized seabirds seen that morning were Cape Petrel Daption capense, Antarctic Prion Pachyptila desolata, Thin-billed Prion P. belcheri, and Soft- plumaged Petrel Pterodroma mollis.

Diet, individual specialisation and breeding of brown skuas (Catharacta antarctica lonnbergi): an investigation using stable isotopes

The diet of brown skuas (Catharacta antarctica lonnbergi) on Bird Island, South Georgia was assessed using a combination of stable isotope analysis (SIA) and mixing model techniques. We found evidence that individual specialisation in diet of adult brown skuas was related to timing of breeding, which may reflect differences in intrinsic quality. Adults with more enriched 13C values hatched chicks earlier than those with depleted 13C values. Individuals with enriched 13C fed predominantly on Antarctic fur seal (Arctocephalus gazella) carrion and placenta while those with lower ratios appeared to rely more on burrowing petrels (e.g. Antarctic prions Pachyptila desolata). Individual foraging differences clearly influenced timing of breeding and potentially the reproductive output of breeding pairs. We confirmed that the main components of the diet of brown skuas during incubation are, in decreasing order of importance, Antarctic fur seal placenta, burrowing petrels and fur seal muscle. In addition, we identified fur seal faeces in the diet during this stage, which had not been detected previously by traditional sampling methods. Finally we identified a correlation in δ13C values between pair members, attributable to the influence of courtship feeding of females by males, or assortative mating according to foraging preference or intrinsic quality.

Lipids from stomach oil of procellariiform seabirds document the importance of myctophid fish in the Southern Ocean

We investigated the relative importance of myctophid fish and Antarctic krill in the diet of adult flying seabirds of the Southern Ocean. The main prey of short‐tailed shearwaters Puffinus tenuirostris (P. ten.), white‐chinned petrels Procellaria aequinoctialis (P. aeq.), blue petrels Halobaena caerulea (H. cae.), thin‐billed prions Pachyptila belcheri (P. bel.), and Antarctic prions Pachyptila desolata (P. des.) were mostly deduced from the lipid analysis of adult stomach oils. More than 97% of the 125 analyzed oils mainly consisted of wax esters (WEs) and triacylglycerols (TAGs) (>70% of total lipids). WE fatty alcohol (FAlc), WE fatty acid (FA), and TAG‐FA profiles clearly segregated P. aeq. from P. ten., with smaller, but still significant, differences among the three other petrel species. P. aeq. and P. ten. therefore preyed on distinct prey species, whereas H. cae., P. bel., and P. des. had a more similar diet, but still with some prey differences. Comparisons between FAlc and FA patterns of oils with those of potential prey species showed that >93% of FAlc and FA patterns of oil WEs had a high probability of resemblance with the myctophid signatures, and similar results were obtained with the TAG fractions. Almost no stomach oil fit the lipid patterns of subantarctic and Antarctic euphausiids, including those of the WE‐rich Thysanoessa macrura and the TAG‐rich Antarctic krill Euphausia superba. This study thus demonstrates for the first time the importance of myctophids in the nutrition of adult flying seabirds breeding in subantarctic islands and foraging in Antarctic waters during the austral summer.

Measurement of Chick Provisioning in Antarctic Prions Pachyptila desolata Using an Automated Weighing System

The frequency and mass of meals delivered to ten Antarctic Prion Pachyptila desolata chicks nesting at Bird Island, South Georgia were examined using automated weighing systems, placed in the nest chamber of the burrow. The weighing systems, which consisted of an artificial nest platform mounted on electronic load cells linked to a data logger, recorded the mass of the chick every 10 min. Meal delivery was concentrated in the first few hours after dark with a peak (45% of meals) in the second hour of darkness. The mean number of meals per night per chick ranged from 0.4 to 1.7 with 80% of chicks receiving at least one meal per night; there were no nights when none of the chicks was fed. Chick 9, which had the highest feeding frequency, received smaller meals (mean 18 g) than all of the other chicks (mean 37 g). The mass of first and second meals delivered in the same night was not different nor was there a relationship between meal mass and feeding frequency (except for chick 9). There was no relationship between meal mass and chick age between 5 and 50 days. Meals delivered following a night when a chick received no meal were larger than when a chick had been fed the previous night. The proportion of chicks receiving 0, 1 and 2 meals per night differed from the predicted binomial distribution, assuming the independence of feeding by both parents, with more chicks receiving one meal per night than expected. Comparison with periodic weighing methods indicates that the latter underestimates meal size and feeding frequency. The variation within the small sample of chicks studied indicates the need for large sample sizes to estimate population provisioning parameters. However, the weighing system was very successful in providing accurate data on chick provisioning and, with additional development, could provide data on the individual provisioning strategies of adult birds.

Natural and Experimental Changes in Chick Provisioning in a Long-Lived Seabird, the Antarctic Prion

The ability of Antarctic Prions Pachyptila desolata to regulate their provisioning effort was studied at Kerguelen Islands by comparing two seasons when food availability differed, and by experimental manipulation of foraging costs. Antarctic Prions provision their chick by a two-fold foraging strategy: on average, they alternate a long foraging trip 7-9 days long when they build up body reserves and then feed the chick, with 2 or 3 successive short trips lasting 1 or 2 days when they use previously stored body reserves to forage for provisioning the chick. Although hatching success and fledging success were similar for the two seasons examined, chicks produced in 1996 grew faster and were heavier at the end of the study than in 1995. The difference was due to a higher provisioning rate in 1996 resulting from long trips being 2 days shorter than in 1995, because the Antarctic waters where adults are believed to feed on Antarctic krill during these long trips were 330 km further away in 1995 than in 1996. While returning from long trips, and during short trips, prions mainly feed close to the colonies on the amphipod Themisto gaudichaudii. This prey was less available in 1995, but prions were able to switch to other prey. Cost of foraging was increased experimentally by adding mass to adults. Loaded parents differed from control parents only by increasing the duration of long foraging trips. The results of both the experiment and the study of the natural variation indicate that the ability of Antarctic Prions to increase provisioning is limited. Birds kept their body mass stable, provided food loads of similar mass and had short foraging trips of similar duration. During long trips they spent longer time foraging either to reach more distant feeding grounds or to cover higher foraging costs. The main constraint on chick provisioning is probably the necessity for birds to maintain a threshold body mass to limit the risk of increased mortality due to breeding effort; the higher yields during long foraging trips permit them to do so.

Interannual Variation in the Diet of the Antarctic Prion Pachyptila desolata at South Georgia

SummaryThe diet of the Antarctic Prion Pachyptila desolata was examined using food samples regurgitated by adult birds during five breeding seasons at Bird Island, South Georgia. In all years the diet was mainly crustaceans, with a small proportion of myctophid fish and trace amounts of cephalopods. Antarctic krill Euphausia superba was the dominant prey item in three years and was replaced by calanoid copepods, especially Rhincalanus gigas and Calanoides acutus, in two years of low krill abundance. Differences in the prey species taken and observations of foraging behaviour suggest that in years of low krill availability Antarctic Prions forage closer inshore, taking copepods by filtering surface water through their palatal lamellae. By switching to feeding on copepods Antarctic Prions are apparently able to maintain a comparable level of reproductive success, unlike most other krill feeding species which suffer much reduced reproductive performance in years of reduced krill availability.

Breeding, Distribution and Status of Barrow-nesting Petrels at Maqaurie Island

A survey of burrow-nesting petrels on Macquarie I. between 1975 and 1982 confirmed breeding of the white-headed petrel Pterodroma lessoni, blue petrel Halobaena caerulea, Antarctic prion Pachyptila desolata, fairy prion Pachyptila turtur, sooty sheanvater Pufinus griseus and common diving petrel Pelecanoides urinatriw. A further six species were recorded. The population size of all burrow-nesting petrels has been adversely modified by alien fauna introduced last century. Of the six species breeding, one is stable, two are diminishing and three are present in very low numbers. Current deterioration of their status is localized and with proper management there may be recovery, particularly of the three last species.