Wilson's Storm Petrel Research Articles

Diet and foraging areas of Southern Ocean seabirds and their prey inferred from stable isotopes: review and case study of Wilson’s storm-petrel

Analysis of stable isotope ratios in animal tissues has emerged as a powerful tool for determining the trophic level and composition of prey and foraging location. We summarize here data on the stepwise trophic enrichment in δ 15 N and latitudinal gradient in δ 13 C in the Southern Ocean, and derive a regression equation to estimate latitudes from δ 13 C values. We analysed isotope ratios of feathers of the small, pelagic seabird Wilson's storm-petrel Oceanites oceanicus, in different breeding stages, in comparison to isotope ratios of 4 other seabird species breeding in close vicinity on King George Island, South Shetland Islands. δ 15 N analysis of feathers and albumen from Wilson's storm-petrels indicated a shift in diet from mainly crustaceans during egg formation to an increased proportion of fish during chick-feeding and moulting. δ 15 N values of Wilson's storm-petrels during the chick-rearing season were closer to the mainly piscivorous-carnivorous skuas than to krill-feed- ing penguins, confirming that fish is an important part of their diet. δ 13 C analysis of feathers identi- fied 4 distinct foraging areas: δ 13 C values in egg-white suggest that egg-forming females moved south to the sea ice edge. This coincides with the distribution of their main prey, Antarctic krill Euphausia superba, during this period. During the breeding season, Wilson's storm-petrels fed in the area around the colony, which is also used by penguins and skuas. δ 13 C of the feathers indicate that adults migrated to the Subtropical Front and beyond (north of 44°S) during the inter-breeding period. Feathers were also analysed from 10 Wilson's storm-petrels caught by mistnet and thought to be pre- breeders because they lacked foot markings; 8 of these had moulted in the same area as breeding birds, while 2 birds had moulted in an area further north (north of 30°S). Adelie penguins Pygoscelis adeliae and Gentoo penguins P. papua had significantly different δ 13 C, suggesting that the Adelie penguins foraged further south than the Gentoo penguins. The foraging areas of brown skuas Ster- corarius antarctica and south polar skuas S. maccormicki could not be separated by their isotope ratios.

Resource allocation in Wilson's storm-petrels Oceanites oceanicus determined by measurement of glucocorticoid excretion

When resources are limited, life-history theory predicts that long-lived animals should allocate available resources to body maintenance rather than to reproduction in order to maximise their lifetime reproductive success. In the present study, we estimated physiological stress in a small procellariiform seabird, the Wilson's storm-petrel Oceanites oceanicus, as a means of understanding how limited resources are partitioned between provisioning parents and their chicks. We analysed adrenocortical activity of Wilson's storm-petrels during the breeding season by measuring glucocorticoid (GC) excretion, using an enzyme immunoassay measuring tetrahydrocorticosterone concentrations in extracts of faeces and urine of chicks and adults. Faecal GC measures were negatively correlated with chick body condition, suggesting that measures of tetrahydrocorticosterone in faeces and urine can be used to assess adrenal activity characteristic for physiological stress in Wilson's storm-petrels. In the breeding season of 1999, the colony was subject to low food availability, and the faecal and urine GC levels of chicks were elevated during these months of chronic starvation. In contrast, adults did not show elevated GC levels. The data thus suggest that Wilson's storm-petrels respond to unfavourable conditions by maintaining their own body condition and reducing provisioning of food to their chicks.

Predicting seabirds at sea in the Southern Indian Ocean

Predictive models were constructed based on at-sea observations of 6 species of sea- birds within the Prydz Bay region of East Antarctica. A spatial logistic model was used, and predic- tions were based on physical environmental data. The hypothesis that these models could predict observations of the same species in the disjunct Vincennes Bay region of East Antarctica was tested. The best results were obtained for the 2 endemic Antarctic breeding species examined (Antarctic and snow petrels). The accuracies of the predictions for Wilson's storm petrels and Cape petrels (which breed both in the Antarctic and on subantarctic islands) were low due to their broad distributions at sea. The predictions for 2 species that breed in subantarctic and temperate localities (white-chinned petrels and prion spp.) were poorest, reflecting the limited seasonal use of Antarctic waters for foraging by these species. The approach is applicable for estimating the probability of observing seabird species in unsurveyed areas of the Southern Ocean, but is likely to be limited to those species breeding regionally, and not for species foraging in the area and breeding elsewhere.

Begging in the absence of sibling competition in Wilson’s storm-petrels, Oceanites oceanicus

Begging displays of nestlings in multichick broods can signal both hunger and competitive ability. Studies of begging in species with single-chick broods exclude the influence of nestling competition and may provide especially useful models for the study of signalling during parent–offspring conflict. However, there is no evidence that chicks signal hunger by begging in the absence of sibling competition. I tested predictions of signalling models in a species with single-chick broods, the Wilson's storm-petrel. Chicks used two types of begging calls, ‘rhythmic’ calls and ‘long’ calls. I found that chicks conveyed information about their current body condition by begging. When their body condition was low, chicks increased the number and frequency of long begging calls, as well as the frequency of rhythmic calling. Parents responded to increased begging by regurgitating larger meals. The study thus demonstrates that the begging system can work in the absence of nestling competition. Chicks also called in the absence of their parents, but in this context they used only rhythmic calls and there was no correlation with current body condition. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Seasonal and annual variation in the diet of breeding and non-breeding Wilson's storm-petrels on King George Island, South Shetland Islands

The diet of breeding and non-breeding Wilson's storm-petrels (Oceanites oceanicus) was analysed over four breeding seasons on King George Island, South Shetland Islands, in order to test if there are changes in diet composition within and between seasons. Krill was the most important food item, followed by myctophid fish and amphipods. Breeding birds showed a clear seasonal pattern of diet, with krill decreasing and alternative prey increasing from the incubation to the chick-rearing period. Non-breeders were not found to change their diet composition. The data suggest that Wilson's storm-petrels selectively choose alternative prey to krill in order to meet the nutrient demands of their chicks. In years of low food availability, Wilson's storm-petrels may have a limited option of prey choice.

The importance of the Patagonian Shelf for top predator species breeding at South Georgia

1. The rich zooplankton, fish and squid resources on the Patagonian Shelf sustain substantial populations of largely resident seabirds and marine mammals. These habitats are also visited seasonally by similar species from elsewhere but few data exist on their status and origin. Recent studies, using satellite-tracking to determine foraging ranges and feeding areas of seabirds and marine mammals breeding at South Georgia, have shown that several species make substantial use of the waters of the Patagonian Shelf. 2. Wandering albatrosses use shelf-edge areas year-round with direct observations of both sexes of almost all age classes, including, breeding, pre-breeding and non-breeding individuals. White-chinned petrels and female Northern and Southern giant petrels mainly visit during incubation and post-breeding, particularly to the Falklands Current (White-chinned petrels) and to upwelling areas around the southern shelf-break from the Burdwood Bank in the east to Staten Island and Diego Ramirez in the west (giant petrels). Northern giant petrel males during incubation and Antarctic fur seals in winter reach inner shelf habitats in the northern sector. In contrast, South Georgia populations of black-browed and grey-headed albatrosses do not appear to use the Patagonian Shelf at any stage of their breeding cycle. 3. Although the use of the Patagonian Shelf by visiting species is now best documented for South Georgia species, recent observational data confirm that seabirds from Diego Ramirez, Tristan da Cunha and Gough visit the southern and northern sectors, during both breeding and non-breeding seasons respectively. Several Antarctic species (notably Antarctic fulmar and cape petrel) winter in the region as do at least two albatross species from New Zealand; other species (especially Wilson's storm petrels) use it as a staging ground on migration, as do several species of baleen whales and possibly other cetacean species. 4. Three of the seabird species which breed on the Patagonian Shelf are Globally Threatened; seven of the visiting species (and four baleen whale species) also have this status. The Patagonian Shelf is, therefore, not only of global importance for the diversity and abundance of its resident top predators but is just as critical for the survival of many visiting species, some of which are even more endangered. 5. Combining data from satellite-tracking with conventional mapping from direct observations offers the prospect of defining the foraging ranges (and the main feeding areas within these) of a range of key top predator species. Such data should be used, in conjunction with similar information of the distributions of fish, squid and zooplankton resources and of fishing effort, to identify critical marine habitats whose precautionary, multiple-use sustainable management will be vital to protect the interests of both commercial fishers and top predators. Copyright © 2002 John Wiley & Sons, Ltd.

Variation in breeding success in Wilson's storm petrels: influence of environmental factors

The climatic and sea ice conditions of the Southern Ocean are highly variable within and between years, and a better understanding of the influence of climatic conditions on the various parts of the marine food chain is needed. This paper summarizes data on breeding success of a krill-dependent predator, the Wilson's storm petrel Oceanites oceanicus, in a colony on King George Island, South Shetland Islands, Antarctica, over four breeding seasons from 1995/1996 to 1999/2000. The seasons differed greatly in environmental conditions and in the resulting food availability which was reflected in inter- and intra-annual variations in feeding frequency. The breeding success was consequently variable. Starvation, the main cause of chick mortality in three out of four breeding seasons was associated with reduced sea ice cover in winter, which is known to depress food availability in the following breeding season. Food delivery rates also depended on the prevailing winds, which drive the transport of zooplankton-rich water masses. Snowstorms caused additional chick mortality in two out of four seasons when nest burrows became blocked. Implications for the use of Wilson's storm petrels for monitoring of krill are considered.

Genetic Monogamy in Wilson's Storm-Petrel

Genetic Monogamy in Wilson's Storm-Petrel

Genetic Monogamy in Wilson's Storm-Petrel

Genetic Monogamy in Wilson's Storm-Petrel

Genetic Monogamy in Wilson's Storm-Petrel

Genetic Monogamy in Wilson's Storm-Petrel

Provisioning and growth in chicks of Wilson's storm-petrels ( Oceanites oceanicus ) on King George Island, South Shetland Islands

We present data on chick growth and chick feeding in Wilson's storm-petrel (Oceanites oceanicus) in a colony on King George Island, South Shetland Islands. Chicks were repeatedly weighed and the weight differences over 24 h were corrected for metabolic loss in order to obtain an estimation of meal sizes. Chicks were fed on 93% of the nights (n=688 nights). The average meal size for a single feeding was 8.5 g. Chicks received on average 1.2 feedings per night. These results are compared with data for this species from other locations. There was a trend for increased meal sizes from northern to southern populations, parallel to an increase in the adult mass, indicating that Wilson's storm-petrels carry optimal meal sizes according to their body size and may take advantage of increased food abundance by increasing feeding frequencies. We describe chick growth and discuss the influence of egg size, hatching date and feeding frequency on chick growth. The egg size had a positive influence on tarsus growth and body mass of chicks. Later-hatched chicks started wing growth and finished mass growth at a younger age and reached lower peak masses, indicating that late chicks may adapt to the restricted breeding season in their Antarctic breeding grounds by a more rapid development, but will fledge with a lower degree of development and less resources.

The use of foot web coloration for the estimation of prebreeder numbers in Wilson's storm-petrels, Oceanites oceanicus

The aim of this study was to develop a method to estimate the proportion of prebreeders in Wilson's storm-petrels (Oceanites oceanicus) in mist-net catches. A comparison of morphological parameters between birds captured on the nest and by mist-net revealed significant differences in two seasonally changeable parameters, body mass and brood patch size, as well as in a parameter independent of the time of the season, the presence of black spots in the yellow areas of the webbed feet. The difference in the occurrence of black markings between birds caught by mist-net and at the nest was highly statistically significant and was used to estimate the proportion of prebreeders, which was 86.6% in a sample of 336 mist-netted birds, compared with 85.3% for the same sample using cloacal measurements. The latter method is only applicable during the time window of the days after egg laying, while the absence of black pigment patches serves as an indicator for the classification of prebreeders throughout the season. This provides the basis for further studies on the behaviour of prebreeding petrels.

A Theoretical Analysis of Sea-anchor Soaring

This study presents a concise mathematical model that accounts for sea-anchor soaring, a special flight technique used by sea birds, in particular storm petrels. Conventional wing theory is used to reveal the mechanics of sea-anchor soaring. The feasibility and existence of an equilibrium are summarized by formulae giving the wind velocity criteria. The stability of the equilibrium is also revealed: among two possible equilibria, the equilibrium at the very low velocity to water is shown to be stable. Numerical examples show the following: sea-anchor soaring is almost always stable; Wilson's storm petrel can soar at 0.256 ms−1in wind with 4.79 ms−1under the best conditions. Larger sea-birds like albatrosses need gusty winds to soar, but such strong winds make the sea choppy and hence prevent soaring. Foot-web size regulates the size of a bird utilizing sea-anchor soaring at low velocities to water.

Coprophagy by Wilson's Storm-petrels, Oceanites oceanicus, on North Atlantic Right Whiale, Eubalaena glacialis, faeces

Coprophagy by Wilson's Storm-petrels, Oceanites oceanicus, on North Atlantic Right Whiale, Eubalaena glacialis, faeces

Stomach Oil and the Energy Budget of Wilson's Storm-Petrel Nestlings

Stomach Oil and the Energy Budget of Wilson's Storm-Petrel Nestlings

Ventilatory Oxygen Extraction in Relation to Ambient Temperature in Four Antarctic Seabirds

We tested the hypothesis that at low ambient temperatures (Ta) birds reduce ventilatory heat loss by increasing ventilatory oxygen extraction (Eo2). We examined relationships between Ta, body temperature, oxygen consumption (V̇o2), carbon dioxide production (V̇co2), evaporative water loss (ṁH2O), respiratory frequency, tidal volume (VT), minute volume, and Eo2, in four species of Antarctic marine birds ranging in body mass from 33-4,915 g The factorial increases in V̇o2 ranged from 1.8 to 5.2 between the lower critical temperature (Tlc; 10° -30° C, depending on species) and a Ta of -23°C. The respiratory exchange ratio (V̇co2/V̇o2) did not change with Ta. The ṁH2O was independent of Ta between 10° and 30° C in kelp gulls and giant petrels but was positively correlated with Ta between 10° and 35° C in Wilson's storm-petrels and between 10° and 30° C in South Polar skuas. Thermal conductance (C) was minimal at Ta's of 10° or 20° C depending on the species and was constant and low at Ta's below this minimum. In all four species C increased significantly at high Ta's. In storm-petrels, gulls, and skuas, the increase in V̇o2, resulting from a change in Ta from Tlc down to -23°C was accommodated mainly by increasing VT. In contrast, in giant petrels the increase in V̇o2 resulting from a change in Ta from Tlc down to -23°C was accommodated mainly by increasing Eo2, and the increase in VT was of secondary importance. Our data suggest that increasing Eo2, as a means of reducing ventilatory heat loss is not a general phenomenon in cold-adapted birds.

A further contribution on the biology of the Antarctic flea, Glaciopsyllus antarcticus (Siphonaptera: Ceratophyllidae)

Experiments showed that adult Antarctic Fleas Gladopsyllus antarcticus preferred dark over light conditions, dry over wet conditions, and fine substrate over coarse substrate. Examination of seabird chicks and collections of nest material indicated that the Southern Fulmar Fulmarus glacialoides, is the major host species of the Antarctic Flea, while Snow Petrels Pagodroma nivea, Cape Petrels Daption capense, Antarctic Petrels Thalassoica antarctica, and Wilson's Storm-Petrels Oceanites oceanicus are minor hosts. This is the first report of Antarctic Fleas occuring on either Antarctic Petrels or Wilson's Storm-Petrels. No fleas were found associated with Southern Giant Petrels Macronectes giganteus, Antarctic Skuas Catharacta maccormicki, or Adelie Penguins Pygoscelis adeliae. No live fleas were found in Southern Fulmar nest material during their period of dispersal over the winter months, supporting the hypothesis that Antarctic Fleas survive the winter period by remaining on their seabird host.

Species-specific recognition in birds: an experimental investigation of Wilson's storm-petrel (Procellariiformes, Hydrobatidae) by means of digitalized signals

Most acoustic studies on birds dealing with species specificity have concerned the territorial function of the song in passerines. We studied species specificity in a non-passerine bird, Wilson's storm-petrel (Oceanites oceanicus). Males of this species attract females by uttering a chattering call, which acts as a premating isolating mechanism. We analysed the encoding of species specificity in the call by measuring the variation in its physical features. We then experimented in the field with played-back computer-synthesized signals and identified the relevant cues that elicited species recognition, namely the modal frequency and the durations of both syllable and silence. We relate our results to species specificity in passerines, and emphasize differences in the responses with respect to sex and status of responding birds, the differences being due to the meaning of the species-specific signal for the receiver.

Calls of Wilson's Storm Petrel: Functions, Individual and Sexual Recognitions, and Geographic Variation

The vocalizations of the Wilson's storm petrel (Class Aves) are described briefly. The functions of these calls was determined by experimental playback. The grating call was highly stereotyped individually, and was used in sexual contexts (short version) or agonistic situations (long version). In contrast, the chattering call, displayed only by males, was used for self-advertisement and species recognition. The geographic variation of calls exhibited between two different populations is discussed.

The diets of five summer breeding seabirds in Ad�lie Land, Antarctica

The diets of five breeding seabird species were investigated on Adelie Land in January–February 1982. Stomach contents of Adelie penguins, Pygoscelis adeliae, were sampled by a water off-loading method and of Procellariiformes by spontaneous regurgitation. Diet compositions by mass were: Adelie penguin (79% euphausiid, 18% fish, 3% squid); Cape pigeon, Daption capense, (64% euphausiid, 29% fish, 7% carrion); Antarctic fulmar, Fulmarus glacialoides, (64% euphausiid, 20% carrion, 16% fish); snow petrel, Pagodroma nivea, (95% fish, 2% euphausiid, 1% carrion) and Wilson's stormpetrel, Oceanites oceanicus, (39% fish, 37% euphausiid, 13% carrion, 12% various crustaceans). The present Adelie penguin diet is consistent with those reported in other studies, given our knowledge of geographical variation in food availability. Differences in the diets of fulmarine petrels appear to relate to differences in foraging areas. The snow petrel is a fish-eating bird associated with pack-ice. Cape pigeon and Antarctic fulmar are mainly krill-eaters and we infer segregation along a neritic/oceanic gradient because of the importance of the neritic Euphausia crystallorophias in the former and the oceanic E. superba in the latter.