Antarctic Petrel Thalassoica Antarctica Research Articles

Variation in Antarctic Petrel Foraging Ecology: Not All Individuals Specialize on Krill

Individual heterogeneity in foraging behaviour determines how individuals and populations respond to changes in the availability and distribution of resources. Antarctic krill Euphausia superba is a pivotal species in Southern Ocean food webs and an important target for Southern Ocean fisheries. Changes in its abundance could dramatically impact marine predators, with effects depending on the extent to which all individuals rely on krill as prey. The Antarctic petrel Thalassoica antarctica is a high latitude seabird thought to be dependent on krill in part of its breeding range. Here, by combining fine-scale GPS tracking of petrel foraging trips with diet data, we examined the level and consistency of inter-individual variation in foraging strategies in breeding Antarctic petrels in Dronning Maud Land, Antarctica, and assessed whether all individuals share a similar reliance on Antarctic krill. We found that Antarctic petrels showed high levels of repeatability in their diet and foraging movements at sea, indicating consistent individual differences in foraging strategies. During consecutive foraging trips, petrels tend to make trips of similar lengths and durations to reach similar terminal locations and to feed on similar prey. These individual differences in diet were spatially structured, with individuals travelling towards the west consuming a more fish-based diet. These different foraging tactics did not appear to be associated with different costs and/or benefits as adult body mass, chick survival and chick growth were unrelated to birds’ foraging movements and diet. Our results show that, even if a large part of the population may be dependent on krill, some individuals specialize on fish. Such inter-individual variation in foraging suggests that this population could be more resilient to changes in the marine environment, such as a decline in krill abundance or a shift in krill distributions.

The same pathway to the Weddell Sea birdlife, after 65 years: similarities in the species composition, richness and abundances

As part of a multi-year study of top predators in Antarctica, we conducted a seabird shipbased survey on board Almirante Irizar icebreaker in the Weddell Sea to the Filchner Ice Shelf in the austral summer 2020. We carried out 10-minute counts along 1843 km during 125 hours of observation. We analyzed the species distributions and the relationships with the ice cover. We registered 15 species of which four represented more than 85% of the total abundance: Antarctic petrel Thalassoica antarctica (43.9%), snow petrel Pagodroma nivea (16.3%), Arctic tern Sterna paradisaea (15.2%) and emperor penguin Aptenodytes forsteri (10.1%). Species distribution and its relationship with ice cover were analyzed statistically. The ice cover concentration was estimated by using satellite images. We compared our results with the first ship-based bird survey conducted up to the Filchner Ice Shelf in the austral summer 1955/56 to analyze possible changes in the bird community over time. Out of 13 recorded species in the 1955/56 cruise, 11 were present in this study with similar abundance proportions. In both cruises, the bird community consisted of a group of non-numerous species associated with icefree waters and another group of very numerous species associated with high concentrations on ice cover. The similarities between the two cruises, spaced 65 years apart, suggest a temporal persistence of the bird community of the central and the southern Weddell Sea that could be explained by the dynamics of the ice cover and the presence of reproductive colonies within the study site. The current environmental warming is alarming in this bird community because more than 85% of all its individuals belong to four species strongly dependent on ice cover.

Foraging tactics in dynamic sea‐ice habitats affect individual state in a long‐ranging seabird

Abstract Individual heterogeneity in diet and foraging behaviour is common in wild animal populations, and can be a strong determinant of how populations respond to environmental changes. Within populations, variation in foraging behaviour and the occurrence of individual tactics in relation to resources distribution can help explain differences in individual fitness, and ultimately identify important factors affecting population dynamics. We examined how foraging behaviour and habitat during the breeding period related to the physiological state of a long‐ranging seabird adapted to sea ice, the Antarctic petrel Thalassoica antarctica. Firstly, using GPS tracking and state‐switching movement modelling (hidden Markov models) on 124 individual birds, we tested for the occurrence of distinct foraging tactics within our study population. Our results highlight a large variation in the movement and foraging behaviour of a very mobile seabird, and delineate distinct foraging tactics along a gradient from foraging in dense pack ice to foraging in open water. Secondly, we investigated the effects of these foraging tactics on individual state at return from a foraging trip. We combined movement data with morphometric and physiological measurements of a suite of plasma metabolites that provided a general picture of a bird's individual state. Foraging in denser sea ice was associated with lower gain in body mass during brooding, as well as lower level of energy acquisition (plasma triacylglycerol) during both brooding and incubation. We found no clear relationship between the foraging tactic in relation to sea ice and the energetic stress (changes in plasma corticosterone), energetic balance (β‐hydroxybutyrate) or trophic level (δ15N). However, a shorter foraging range was related to both the energetic balance (positively) and the trophic level (negatively). Our results highlight a diverse range of foraging tactics in relation to sea ice in Antarctic petrels. While the various foraging tactics do not seem to strongly alter energetic balance, they may affect other aspects of Antarctic petrels' physiology. Future changes in sea‐ice habitats can thus be expected to have an impact on the individual state of seabirds such as Antarctic petrels, which could ultimately affect their population dynamics. Nonetheless, strong individual heterogeneity in the use of sea‐ice habitats by a typical pagophilic species might strengthen its resilience to environmental changes and in particular to forecasted sea‐ice loss. A free Plain Language Summary can be found within the Supporting Information of this article.

Mercury exposure and short-term consequences on physiology and reproduction in Antarctic petrels

Mercury (Hg) is a pervasive contaminant reaching Antarctic environments through atmospheric transport and deposition. Seabirds as meso to top predators can accumulate high quantities of Hg through diet. Reproduction is one of the most sensitive endpoints of Hg toxicity in marine birds. Yet, few studies have explored Hg exposure and effects in Antarctic seabirds, where increasing environmental perturbations challenge animal populations. This study focuses on the Antarctic petrel Thalassoica antarctica from Svarthamaren, Antarctica, where the world's largest breeding population is thought to be in decline. Hg and the stable isotopes of carbon (δ13C, proxy of feeding habitat) and nitrogen (δ15N, trophic position/diet) were measured in red blood cells from 266 individuals over two breeding years (2012–13, 2013–14). Our aims were to 1) quantify the influence of individual traits (size and sex) and feeding ecology (foraging location, δ13C and δ15N values) on Hg exposure, and 2) test the relationship between Hg concentrations with body condition and breeding output (hatching success and chick survival). Hg concentrations in Antarctic petrels (mean ± SD, 0.84 ± 0.25, min-max, 0.42–2.71 μg g−1 dw) were relatively low when compared to other Antarctic seabirds. Hg concentrations increased significantly with δ15N values, indicating that individuals with a higher trophic level (i.e. feeding more on fish) had higher Hg exposure. By contrast, Hg exposure was not driven by feeding habitat (inferred from both foraging location and δ13C values), suggesting that Hg transfer to predators in Antarctic waters is relatively homogeneous over a large geographical scale. Hg concentrations were not related to body condition, hatching date and short-term breeding output. At present, Hg exposure is likely not of concern for this population. Nevertheless, further studies on other fitness parameters and long-term breeding output are warranted because Hg can have long-term population-level effects without consequences on current breeding success.

Seabird hotspots on icebergs in the Amundsen Sea, Antarctica

Our long-term study on the quantitative at-sea distribution of the upper trophic levels—seabirds and marine mammals—in polar ecosystems aims at quantifying the factors influencing their distribution as well as detecting possible spatial and temporal evolutions, with special attention to hydrography and to global climate changes. During the PS75 (ANT-XXVI/3) expedition of icebreaking RV Polarstern in February–March 2010, 6660 seabirds belonging to 11 identified species were recorded in the Amundsen Sea Embayment and Pine Island Bay during 760 half-hour transect counts. The most numerous species were by far Antarctic petrel Thalassoica antarctica, Adelie penguin Pygoscelis adeliae and snow petrel Pagodroma nivea representing together more than 80% of the total for the whole expedition (n = 5475). Substantial seabird hotspots were concentrated on three icebergs, representing 44% of all observations: 85% of the Antarctic petrels and 40% of the snow petrels. Moreover, 35 Cape petrels Daption capense capense were noted in the immediate surrounding of another iceberg (33% of the total). The highest overall counts were tallied on two icebergs: 250 Antarctic petrels and 500 snow petrels on the first one, and 1000 Antarctic petrels on the second. These hotspots seem to be typical for autumn situations and thus probably reflect the existence of pre-migratory gatherings following the breeding season. The consequences of these high local concentrations and thus the heterogeneity and non-normal distribution of the data are discussed, calculating mean values, standard deviation and density have very questionable value.

At-Sea Distribution and Prey Selection of Antarctic Petrels and Commercial Krill Fisheries.

Commercial fisheries may impact marine ecosystems and affect populations of predators like seabirds. In the Southern Ocean, there is an extensive fishery for Antarctic krill Euphausia superba that is projected to increase further. Comparing distribution and prey selection of fishing operations versus predators is needed to predict fishery-related impacts on krill-dependent predators. In this context, it is important to consider not only predators breeding near the fishing grounds but also the ones breeding far away and that disperse during the non-breeding season where they may interact with fisheries. In this study, we first quantified the overlap between the distribution of the Antarctic krill fisheries and the distribution of a krill dependent seabird, the Antarctic petrel Thalassoica antarctica, during both the breeding and non-breeding season. We tracked birds from the world biggest Antarctic petrel colony (Svarthamaren, Dronning Maud Land), located >1000 km from the main fishing areas, during three consecutive seasons. The overall spatial overlap between krill fisheries and Antarctic petrels was limited but varied greatly among and within years, and was high in some periods during the non-breeding season. In a second step, we described the length frequency distribution of Antarctic krill consumed by Antarctic petrels, and compared this with results from fisheries, as well as from diet studies in other krill predators. Krill taken by Antarctic petrels did not differ in size from that taken by trawls or from krill taken by most Antarctic krill predators. Selectivity for specific Antarctic krill stages seems generally low in Antarctic predators. Overall, our results show that competition between Antarctic petrels and krill fisheries is currently likely negligible. However, if krill fisheries are to increase in the future, competition with the Antarctic petrel may occur, even with birds breeding thousands of kilometers away.

Large‐scale oceanographic fluctuations drive Antarctic petrel survival and reproduction

Polar Regions are experiencing environmental changes at unprecedented rates. These changes can spread throughout entire food webs from lower trophic levels to apex predators. As many top predators forage over large areas, these indirect effects may be associated with large‐scale patterns of climate variability. Using global climate indices that are known to impact the Southern Ocean ecosystem (the El Niño Southern Oscillation and Antarctic Oscillation Indices) we assessed their efficacy to predict variation in the demographic parameters of Antarctic seabirds. First, we used a long‐term dataset on adult survival (estimated from capture–mark–recapture data) and reproduction of Antarctic petrel Thalassoica antarctica, from the largest known breeding colony (Svarthamaren, Dronning Maud Land) and examined whether large‐scale oceanographic fluctuations impact survival and reproduction. Second, we conducted an exhaustive literature review to determine whether the effects of large‐scale environmental variability on Antarctic seabirds have a coherent fingerprint across the Antarctic continent and nearby islands. We found that most of the variation in both reproductive success, timing of hatching, and survival of Antarctic petrels can be accurately modeled using the two modes of large‐scale climate variability in Antarctica. The literature review, combined with the results from our field study, suggests that while the anticipated trends in the global patterns of climatic variability will generally have detrimental effects on populations of top predators in the Southwest Atlantic, these conclusions cannot be extrapolated to all seabird populations in Antarctica without additional data.

Breeding strategies of Antarctic PetrelsThalassoica antarcticaand Southern FulmarsFulmarus glacialoidesin the high Antarctic and implications for reproductive success

Breeding strategies of two closely related fulmarine petrels were studied on Ardery Island, on the continental coast of East Antarctica, where short summers are expected to narrow the time‐window for reproduction. Both species had a similar breeding period (97 days from laying to fledging) but Antarctic PetrelsThalassoica antarcticabred up to 16 days earlier than Southern Fulmars. During the pre‐laying exodus, all Antarctic Petrels deserted the colony, whereas some Southern FulmarsFulmarus glacialoidesremained. Antarctic Petrels exhibited stronger synchronization in breeding, made longer foraging trips and spent less time guarding their chicks than Southern Fulmars. Overall breeding success of both species was similar but failures of Antarctic Petrels were concentrated in the early egg‐phase and after hatching, when parents ceased guarding. Southern Fulmars lost eggs and chicks later in the breeding cycle and so wasted more parental investment in failed breeding attempts. Different breeding strategies may be imposed by flight characteristics; Southern Fulmars are less capable of crossing large expanses of pack ice and need to delay breeding until the sea ice retreats and breaks up. However, due to the short summer they risk chick failure when weather conditions deteriorate late in the season.

Stable isotope ratios of Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) bone collagen

This study investigated the trophic hierarchy status of the Antarctic petrel (Thalassoica antarctica) and snow petrel (Pagodroma nivea) within the Southern Ocean food-web off Dronning Maud Land, Antarctica. During 1991/92 ten Antarctic petrel and ten snow petrel carcasses were collected from Jekselen (71°59′S, 02°35′W) and Robertskollen (71°28′S, 03°15′W) respectively, in the northern Ahlmannryggen, Dronning Maud Land. Collagen from the dense bone of the humeri of these carcasses was extracted and the stable carbon and nitrogen isotope ratios of these samples determined. The snow petrel bone collagen samples displayed a mean δ13C value of −23.9±0.7 (range: −24.7 to −22.9; n=9) and a mean δ15N value of 15.2±1.6 (range: 12.9 to 18.4; n=10). The corresponding values for Antarctic petrel bone collagen were −24.8±1.0 (range: −26.2 to −22.8; n=9) and 13.2±0.6 (range: 12.5 to 13.9; n=8) respectively. The difference between the species’ δ13C values may indicate differences in their foraging habitat. It has previously been suggested that the snow petrel has a higher wing loading than other Procellariiforme species, making the snow petrel less adapted to pelagic foraging than related species and more likely to forage close to the sea ice edge. Algae growing under sea ice apparently can have comparatively high δ13C values, possibly due to growing under carbon dioxide limited conditions. If so, animals foraging close to the sea ice edge might be expected to show higher δ13C values in their body tissues than animals foraging farther out over the open ocean. However, the high δ13C of snow petrel collagen is possibly more likely to be related to the correspondingly high δ15N values found in this tissue, and hence caused by snow petrels including offal from high trophic level Antarctic mammals and birds in their diet.

Breeding biology of high‐latitude Antarctic fulmarine petrels (Procellariidae)

AbstractThis paper provides basic information about the breeding biology of four species of Antarctic fulmarine petrels breeding in the Rauer Islands, East Antarctica: Antarctic fulmar Fulmarus glacialoides, Antarctic petrel Thalassoica antarctica, Cape petrel Daption capense, and snow petrel Pagodroma nivea. Timing and duration of the nesting cycle, incubation and nestling periods, and timing of breeding were determined over three consecutive breeding cycles. Comparing these data with those of other populations revealed that the duration of breeding showed little interannual and spatial variation within the four species. The length of the breeding period varied between the species, with incubation period and nesting cycle length positively related to adult body mass. Nestling period length also differed between the species but was unrelated to adult body mass. Breeding period lengths for these fulmarine petrels were shorter than those for other procellarids and albatrosses. Compressed and invariant breeding cycles of Antarctic fulmarine petrels may have evolved in response to a short season which limits breeding and to opportunities presented by highly abundant food sources.

Aspects of the Ecology of South Polar Skuas Catharacta maccormicki at Hop Island, Rauer Group, East Antarctica

SummaryAspects of the ecology of South Polar Skuas Catharacta maccormicki were investigated at Hop Island, Rauer Group, East Antarctica between December 1990 and February 1991. Data were obtained from pairs across the island generally for comparison with skuas (fringe-dwellers) nesting away from Adélie Penguin Pygoscelis adeliae colonies. While most defended territories included colonies of Adélie Penguins, Antarctic Petrels Thalassoica antarctica or Southern Fulmars Fulmarus glacialoides, others held no surface-nesting seabirds; however, all skuas took penguin material. Activities of two fringe-dwelling pairs, whose territories included fulmars, and fulmars and petrels, were intensively monitored; behaviours were associated mostly with brooding, vigilance or foraging. Foraging trips were longer and less frequent where only fulmars bred, but hunting success was similar to that of the pair hunting in petrel and fulmar colonies. The small number of fringe-dwelling pairs produced proportionally fewer chicks than others; the need to forage away from nesting areas, and to obtain penguin material, even when feeding territories include Antarctic Petrels and or Southern Fulmars, indicates the lower quality of their territories (which may vary). Breeding and other activities are considered in relation to breeding chronology of other local seabirds: the breeding success of fringe-dwellers may be modified by that of neighbouring seabird colonies.

Fulmarine Petrels and South Polar Skua Catharacta maccormicki Populations on Ardery Island, Windmill Islands, Antarctica

The Ardery and Odbert Islands, Antarctica (66°22′S, 110°27′E) have been declared a Specially Protected Area (SPA) because of their breeding populations of species of fulmarine petrels. Published information on the bird life in this SPA was summarised by Bonner & Lewis-Smith (1985) and van Franeker et al. (1990). During the summer 1995/96, a survey of the distribution and numbers of fulmarine petrels and South Polar Skuas Catharacta maccormicki on Ardery Island was undertaken for comparison with previous surveys. Population counts on the island were made from 20–31 December 1995, during early incubation for most species. We counted the number of ‘apparently occupied nest sites’ (van Franeker et al. 1990) of Southern Fulmar Fulmarus glacialoides, Antarctic Petrel Thalassoica antarctica, and Cape Petrel Daption capense breeding in the open. In a couple of locations populations were estimated. For Snow Petrel Pagodroma nivea, the breeding population was considered to equal number of pairs sitting on rocks at dusk, a period when they often sit at nest entrances (Marchant & Higgins 1990).

Body mass and parental decisions in the Antarctic petrel Thalassoica antarctica : how long should the parents guard the chick?

In Procellariiformes, the parents guard the chick after it has attained homeothermy. This strategy may reduce the probability that a small chick is taken by predators, but is costly as only one parent can forage at a time. The decision to leave the chick may therefore be a compromise between the chick's vulnerability to predators, the body condition of the parent on the nest and whether the foraging parent returns in time. We studied how the number of days that parents guarded the chick was related to the body mass of the parent at the nest and the time the foraging parent spent at sea in the Antarctic petrel Thalassoica antarctica. We also examined how the body mass of the parent on the nest and the duration of the foraging trips influenced the chicks' body condition at the end of the guarding period. When the foraging parent did not return to the nest in time to relieve its mate, the number of days the parent on the nest kept guarding the chick was positively related to its body mass on arrival in the colony. The number of days the foraging parent spent at sea was positively related to the body mass of its mate, but those that returned in time had a shorter stay at sea relative to their mate's body mass than those that did not return before their mate had left. Apparently, both the body mass of the parent at the nest and the ability of the foraging parent to adjust its stay at sea to the mate's body mass is important for the number of days the parents guard the chick and also the chick's body condition at this point. The inability to return to the nest before the mate has left may be the result of needing a minimum amount of time at sea to find food, or because some parents having low foraging success and therefore prolong their stay at sea.

Diet and prey consumption of Antarctic petrels Thalassoica antarctica at Svarthamaren, Dronning Maud Land, and at sea outside the colony

The diet of the Antarctic petrel Thalassoica antarctica was studied during two seasons at Svarthamaren, an inland colony in Dronning Maud Land, Antarctica, and in the pack ice off the coast of Svarthamaren. The most important food (wet mass) at Svarthamaren was crustaceans (67%), fish (29%) and squid (5%); however, individuals collected in the pack ice took mostly fish (87%). The prey composition and lengths of prey are comparable to what has been documented in other studies on this species. Estimates of food consumption by birds breeding at Svarthamaren (ca. 250,000 pairs) suggest that approximately 6500 tonnes of crustaceans, 2800 tonnes of fish and 435 tonnes of squid are consumed during the breeding season. The annual consumptions of these birds are estimated to be 34,100 tonnes of crustaceans, 14,700 tonnes of fish, and 2300 tonnes of squid. Satellite telemetry data indicate that Antarctic petrels from Svarthamaren may fly more than 3000 km during one foraging trip, and thus may cover a huge ocean area to obtain their prey.

Reproductive Effort in the Antarctic Petrel Thalassoica antarctica; The Effect of Parental Body Size and Condition

Reproductive Effort in the Antarctic Petrel Thalassoica antarctica; The Effect of Parental Body Size and Condition

Pelagic distribution and numbers of the Antarctic petrelThalassoica antarctica in the Weddell Sea during spring

Pelagic distribution and numbers of the Antarctic petrelThalassoica antarctica in the Weddell Sea during spring

Pelagic distribution and numbers of the Antarctic petrel Thalassoica antarctica in the Weddell Sea during spring

Estimates of the population size of the Antarctic petrelThalassoica antarctica are hampered by its breeding locations in remote nunatak areas of the Antarctic continent. Studies at sea can provide additional information on numbers. Seabird censuses during spring 1992 showed few Antarctic petrels in the western part of the Weddell Sea, but high numbers east of the South Sandwich Islands. The vast majority of the birds occurred in a band of 300 km north to 150 km south of the outer ice edge. Numbers at sea fluctuated in agreement with synchronized colony attendance patterns in the pre-breeding phase and peaked shortly before egglaying when colonies are completely deserted. In this period, densities of Antarctic petrels in the marginal ice zone suggest that at least 2.7±0.5 million individuals occur in the Weddell Sea. It is likely that similar numbers occur immediately east of the study area. The distribution of the petrels matches the location, but not the size, of known breeding colonies in Dronning Maud Land and Coats Land, which suggests that important colonies in this area remain to be discovered. The observations imply that Antarctic petrels in the Weddell Sea commute over ice a surprisingly large distance of at least 2,000 km for a single pre-breeding visit to the colonies.

Regulation of Food Provisioning in the Antarctic Petrel Thalassoica antarctica

Life-history theory predicts that individual birds should invest in reproduction according to their current body condition and the future prospects for survival and reproduction. Thus, it could be expected that current adult body condition should significantly influence food provisioning rates, food loads and concurrent chick growth in the Antarctic petrel. In order to study the significance of parental body condition I correlated meal sizes, feeding frequencies and chick growth with the body condition of the parents. There was a strong correlation between the average meal size delivered to a chick and its growth rate. Adult body condition at the time of hatching was strongly correlated with the average size of meals delivered to individual chicks. Male and female body condition at the time of hatching and average body condition of the pair at the first incubation shift and at hatching significantly influenced the body mass of the chick on day 30. Male body condition and the average body condition of the pair correlated significantly with the growth rate of the chick. The difference in body mass at the age of 30 days of chicks from parents with good body condition compared with chicks from parents with poorer body condition was nearly double that expected. The results strongly suggest that the effort spent during the chick-rearing period, and thus reproductive success, is regulated by the body condition of the parents.

Incubation and brooding performance of the Antarctic Petrel Thalassoica antarctica at Svarthamaren, Dronning Maud Land

Antarctic Petrel Thalassoica antarctica incubation and brooding effort was studied at Svarthamaren, Dronning Maud Land, during the austral summer of 1991–1992. The females probably left the nest site shortly after egg laying. The duration of incubation and brooding shifts as well as the daily weight loss (absolute and proportionate) were comparable with those of other similar‐sized procellariform species. Males spent more time incubating and brooding than did females, suggesting higher female energy stress due to egg laying. Incubating birds which were below average weight were likely to desert the nests before their mates returned from feeding trips. Both males and females lost approximately one‐fifth of their body‐weight during their first incubation shifts. Nevertheless, they increased their initial weights from egg laying to hatching and had their highest initial weights when they returned to start the shift during which the egg hatched. No factors related to adult body‐weight explained the duration of the incubation shifts. Both males and females gained weight at a higher rate when at sea than they lost it during incubation, and it is suggested that factors unrelated to food availability or individual feeding skills may be important in regulating the duration of the incubation shifts and the stay at sea.

Regulation of parental investment in the Antarctic petrel Thalassoica antarctica: an exchange experiment

An experiment was conducted on the Antarctic petrel to test whether the parents were able to respond to changes in food demand of their offspring. Two experimental groups were formed by replacing eight 20-day-old chicks with 10-day-old chicks, and vice versa. The growth rate of chicks in the experimental groups was compared with that in two control groups with chicks of known age. The growth rate of 10-day-old chicks in the nests of parents which initially had 20-day-old chicks did not differ significantly from that in their respective control groups. This indicates that those parents were able to raise a new young nestling, despite having already raised another chick from hatching to 20 days. However, the 20-day-old chicks placed in nests with 10-day-old chicks had a significantly lower growth rate than their control group. Feeding rate per day and nest did not differ significantly among any of the groups. This suggests that the observed difference in growth rate between 20-day-old chicks is related to a lower amount of food delivered per visit to experimental chicks. Thus, in the Antarctic petrel, the feeding rate apparently is not regulated by the status of the chick, but by the parents' ability to gather food or willingness to provide food for the chicks.