Factors affecting chick growth in the South Polar Skua (Catharacta maccormicki): food supply, weather and hatching date

Taxonomic recommendations for British birds: seventh report

Antarctica is free of urbanisation, however, 40 year-round and 32 seasonal Antarctic stations operate there. The effects of such human settlements on Antarctic wildlife are insufficiently studied. The main aim of this study was to determine the organization of the bird population of the Mirny Station. The birds were observed on the coast of the Davis Sea in the Mirny (East Antarctica) from January 8, 2012 to January 7, 2013 and from January 9, 2015 to January 9, 2016. The observations were carried out mainly on the Radio and Komsomolsky nunataks (an area of about 0.5 km). The duration of observations varied from 1 to 8 hours per day. From 1956 to 2016, 13 non-breeding bird species (orders Sphenisciformes, Procellariiformes, Charadriiformes) were recorded in the Mirny. The South polar skuas (Catharacta maccormicki) and Adélie penguins (Pygoscelis adeliae) form the basis of the bird population. South polar skuas are most frequently recorded at the station. Less common are Brown skuas (Catharacta antarctica lonnbergi) and Adélie penguins. Adélie penguins, Wilson's storm petrels (Oceanites oceanicus), South polar and Brown skuas are seasonal residents, the other species are visitors. Adélie penguins, Emperor (Aptenodytes forsteri), Macaroni (Eudyptes chrysolophus) and Chinstrap penguins (Pygoscelis antarctica), Wilson's storm petrels, South polar and Brown skuas interacted with the station environment, using it for comfortable behavior, feeding, molting, shelter from bad weather conditions, and possible breeding. South polar and Brown skuas tend to be attracted to the station, while other Antarctic bird species are indifferent to humans. Birds spend part of the annual cycle at the station or visit it with different frequency, but they cannot meet their ecological needs there all year round. The study improves our understanding of the regularities of the phenomenon of urbanization of the avifauna in the polar regions of the planet Earth.

We studied how environmental conditions affect reproduction in sympatric skua species that differ in their reliance on marine resources: the exclusively marine foraging south polar skua Catharacta maccormicki, the terrestrially foraging brown skua C. antarctica lonnbergi and mixed species pairs with an intermediate diet. Egg size, clutch asymmetry and hatching dates varied between species and years without consistent patterns. In the south polar skuas, 12 to 38% of the variation in these parameters was explained by sea surface temperature, sea ice cover and local weather. In mixed species pairs and brown skuas, the influence of environmental factors on variation in clutch asymmetry and hatching date decreased to 10–29%, and no effect on egg size was found. Annual variation in offspring growth performance also differed between species with variable growth in chicks of south polar skuas and mixed species pairs, and almost uniform growth in brown skuas. Additionally, the dependency on oceanographic and climatic factors, especially local wind conditions, decreased from south polar skuas to brown skua chicks. Consistent in all species, offspring were more sensitive to environmental conditions during early stages; during the late chick stage (>33 d) chick growth was almost independent of environmental conditions. The net breeding success could not be predicted by any environmental factor in any skua species, suggesting it may not be a sensitive indicator of environmental conditions. Hence, the sensitivity of skuas to environmental conditions varied between species, with south polar skuas being more sensitive than brown skuas, and between breeding periods, with the egg parameters being more susceptible to oceanographic conditions. However, during offspring development, local climatic conditions became more important. We conclude that future climate change in the Maritime Antarctic will affect reproduction of skuas more strongly through changes in sea ice cover and sea surface temperature (and the resulting alterations to the marine food web) than through local weather conditions.

Several aspects of the skua display were examined to determine their species specificity. Acoustical parameters were examined for 70 calls of 24 South Polar Skuas (Catharacta maccormicki) and 61 calls of 17 Brown Skuas (C. lonnbergi) at Palmer Station, Antarctica. I found no significant species differences in composition (notes/call), duration, or note duration. Despite large range overlaps, the species differed significantly in four parameters. On average, South Polar Skua notes had a faster repetition rate, lower pitch, lower average frequency, and more harmonics than those of Brown Skuas. Differences among individuals were apparent for all acoustic parameters, but again were most marked for note repetition rate, pitch, average frequency, and number of harmonics. Film analysis of 109 calls made by over 30 South Polar Skuas and of 44 calls made by 12 Brown Skuas revealed that South Polar Skuas tended to lean farther back at some point in the display. About 25% of the birds, however, gave displays that some previous researchers considered atypical for these species, and more than 36% of the birds showed intra-individual variation in display postures. Variation limits the value of these visual and acoustic aspects of the display for individual and species recognition of skuas at Palmer. The value of these parameters for answering evolutionary and taxonomic questions about skuas, however, has yet to be assessed. Skuas (Stercorariidae) have been the subject of taxonomic controversy at both the generic and specific levels for well over a century (Pietz 1984). I follow Brooke (1978) in separating skuas (Catharacta) from jaegers (Stercorarius) on the basis of derived juvenal plumage characteristics. Within the genus Catharacta, the taxonomic picture is more complicated; morphological features do not provide clear bases for making some taxonomic decisions. Currently, at least five groups are recognized as either species or sub-species. These include the Great Skua (C. skua) of the North Atlantic, the Chilean and Falkland skuas (chilensis and antarctica, respectively) of southern South America, the Brown Skua (lonnbergi) of the sub-Antarctic, and the South Polar Skua (maccormicki) of the Antarctic. Based on morphological characteristics, some authorities lump the Falkland, Brown, and Great skuas and assign full species status to both the Chilean and South Polar skuas. Hybridization has been documented, however, between Chilean and Falkland skuas (Devillers 1978), and between Brown and South Polar skuas (Watson et al. 1971, Parmelee et al. 1977) in their respective zones of sympatry. Pending resolution of their taxonomy, I will refer to them all as separate species. Overlaps in size and plumage characteristics among geographically distant populations of these groups have been recognized (Hamilton 1934, Murphy 1936). As a result, there is interest in using other traits for species identification, and for evaluating evolutionary and taxonomic relationships in this genus. Some biologists (e.g., Watson 1975, Devillers 1978, Jouventin and Guillotin 1979) have suggested that acoustic and visual aspects of the skua's long call display (Moynihan 1955) may help to distinguish species. The display, as described by num rous authors (e.g., Stonehouse 1956, Perdeck 1960, Moynihan 1962, Burton 1968, Spellerberg 1971, Devillers 1978), is by far the most visible and audible display of those in the skua's behavioral repertoire. It is also one of the most common, employed for territorial advertisement as well as for greeting mates. Moynihan (1955) considered this display to be homologous with the and oblique po tures of gulls. Visual components typically associated with the skua's include ing raising (Perdeck 1960) and the bent n ck (Moynihan 1962), as well as the oblique. The display resulting from the integration of th se components is sometimes referred to as he long complex, and several variations have been noted in the sequencing of components (Perdeck 1960, Spellerberg 1971). With respect to its multiple functions, the skua's is analogous to that of many

Growth and survival of altricial young are influenced by their parents’ abilities to invest in a breeding attempt. As a result, chick growth and survival in one breeding season may be indicative of their parents’ long-term reproductive potential. To determine whether variation in long-term reproductive success is driven by differential breeding investment, parental care and chick growth in wandering albatrosses (Diomedea exulans) were correlated with parental historical reproductive success. Effects of age and breeding experience (determined from past breeding attempts) and pre-laying body condition (mass–size indices) on chick growth and survival also were tested. Longer brooding of chicks increased their survival, but length of chick brooding did not differ between historically unproductive and successful breeders. Past reproductive success also was not correlated with chick growth rates or fledging mass or size. Chick brooding period, chick growth rates, final mass and size were independent of parental body condition. Older and more experienced parents brooded chicks for longer and their chicks grew faster, supporting previous findings that breeding competence is a learnt skill. Chick care and growth characteristics differed more between than within pairs, suggesting that differences in these characteristics are driven by variation among pairs.

One of the most important measures of offspring performance is growth rate, which is often traded off against another important survival trait, immune function. A particular feature of ostrich chicks maintained in farmed environments is that cohorts of chicks vary widely in size. As parents can have a profound effect on the phenotype and fitness of their offspring, we investigated whether chick growth and immune defence were related to variation in levels of immune defence in their genetic parents. As secondary sexual traits of sires could serve as indicators of male quality, and be used in female mating decisions, we also investigated whether chick growth rate and immune defence were related to male plumage and integumentary colouration. We found that offspring growth rates and humoral responses were related to the humoral responses of their parents, suggesting that at least some components of humoral immune capacity are heritable. The white colour of male ostrich feathers was correlated to the humoral response and growth rate of their offspring, suggesting that this visual cue involved in the male courtship display could serve as an important signal to females of male quality, thereby forming the basis of mate choice in this species.

Mass loss of chick‐rearing birds can be the direct consequence of physiological stress (reproductive stress hypothesis) or an adaptive mass adjustment in response to the increased demands on flight efficiency during the flight‐intensive chick‐rearing period (adaptive mass loss hypothesis). To test which of these hypotheses best explains mass loss in South Polar Skuas Stercorarius maccormicki rearing chicks, a food supplementation experiment was carried out in the austral summer 2000/01 at King George Island, Antarctica. Half of the breeding pairs were fed about 20% of the chick's daily energy demand every second day and chick growth and adult nest attendance were recorded. Parents were caught at the start and the end of chick‐rearing to calculate adult mass loss. Male parents of food‐supplemented pairs attended their nest territories more than control males but females kept their attendance constant. Chick growth was only minimally affected and the treatment probably had no fitness consequences. Male Skuas in control pairs had a higher deviation from the body size–mass regression at the end of chick‐rearing compared with the start, supporting the stress hypothesis, whereas female deviation remained unchanged. Males of food‐supplemented pairs were heavier than unsupplemented males at the end of the breeding cycle but not significantly so. Food‐supplemented females were lighter at the end, supporting the adaptive mass loss hypothesis. Adult mass loss is thus best explained by the reproductive stress hypothesis in males but by the adaptive mass loss hypothesis in females. However, the two hypotheses are not mutually exclusive and the results do not exclude the possibility that mass loss in females is stress‐induced but the amount of mass lost is an adaptive adjustment to the reliability of the food supply. The finding that members of a breeding pair may follow different strategies of mass adjustment has implications for the use of mass loss as an index of parental effort. Without knowing which strategy each sex has adopted it is of little use to compare mass loss between parents.

Where South Polar Skuas (Stercorarius maccormicki) occur in the absence of Brown Skua (S. antarcticus), their main prey consists of other birds. In contrast, where the two species occur together, fish appears to dominate the diet of South Polar Skuas, probably because Brown Skuas monopolise the terrestrial resources. Twenty-eight stomach samples of South Polar Skuas were collected throughout the breeding season at Half Moon Island, South Shetland Islands, Antarctica. Fish were the most dominant prey item (100% frequency, 98% prey mass); their importance remained constant throughout the study period. Although there is a colony of Chinstrap Penguin (Pygoscelis antarctica) nearby the South Polar Skua population and there are very few Brown Skuas, the South Polar Skuas did not eat penguins. The result suggests fish are selected preferentially over terrestrial resources, at least in certain regions, and particularly when availability of terrestrial resources is limited. Thus, competitive exclusion by Brown Skuas may not fully explain dietary choice of South Polar Skuas.

-We studied the ecology and behavior of pelagic seabirds in the Eastern Tropical Pacific (1984-1992). We hypothesize that the absence of kleptoparasitism (hereafter parasitism) by jaegers and skuas (subfamily Stercorariinae, hereafter skuas) on Kermadec Petrels (Pterodroma neglecta) and Herald Petrels (P. arminjoniana) observed in this study, compared to regular attack on procellariids of similar size, resulted from Batesian mimicry by the former of skuas. As mimics of skuas, Kermadec and Herald petrels avoided being kleptoparasitized because skuas do not parasitize conspecifics. We also document regular parasitism by Kermadec Petrels on other large procellariids, and further hypothesize that this petrel is successful as a parasite because it is a foraging mimic of the subadults of the larger skuas (Pomarine Jaegers [Stercorarius pomarinus] and South Polar Skuas [Catharacta maccormicki]) through its similarity of color pattern, flight profile, and behavior when initiating an attack, and because the large skuas (its models) are very effective as parasites. This petrel's incidence of attack and frequent use of alternate feeding methods suggests that it is a less specialized parasite than are the skuas. Kermadec Petrels prefer the same hosts and use a similar method of attack as do the large skuas, which achieve a very high rate of success in the Eastern Tropical Pacific because of their ability to threaten hosts through size-mediated aggressiveness. The Kermadec Petrel is smaller or similar in size to its preferred hosts and is not as aggressive as large skuas, but its rate of success as a parasite is higher than expected. Received 1 September 1991, accepted 22 June 1992. KLEPTOPARASITISM (hereafter termed parasitism) is a well-known feeding method of seabirds, particularly for skuas (Catharacta spp.) and jaegers (Stercorarius spp.; subfamily Stercorariinae, hereafter referred to collectively as skuas), frigatebirds (Fregata spp.), gulls (Larus spp.) and, to a lesser extent, terns (Sterna spp.), boobies (Sula spp.), pelicans (Pelecanus spp.), cormorants (Phalacrocorax spp.), and members of the Procellariiformes (reviewed by Furness 1987a, b, Duffy 1980, 1982, 1989). In procellariiforms, the use of parasitism as a regular means of feeding has been described only in the Waved Albatross (Diomedea irrorata; Duffy 1980), and no procellariiform parasite has been known to tenaciously pursue hosts as do skuas, the most highly evolved of avian parasites. Herein, we describe skualike parasitism by a procellariid, the Kermadec Petrel (Pterodroma neglecta). Parasitism by Parasitic Jaegers (S. parasiticus), Great Skuas (C. skua), and South Polar Skuas (C. maccormicki) has been studied extensively on the breeding grounds (reviewed in Furness 1987a, b) and at a coastal estuary on the migratory route (Parasitic Jaeger; Taylor 1979). However, few studies have documented the foraging behavior of skuas away from the breeding grounds, other than species parasitized at given locations (but see Duffy 1980, Sinclair 1980, Furness 1983). Skuas possess a distinct and highly conspicuous white patch in the inner primary region of their otherwise dark-colored wings (Harrison 1987, Olsen 1989). In flight, this mark can be seen at a great distance at any angle except when the birds are flying directly toward, or away from, the observer. As a result of this distinctive feature, and the tenacious, aggressive, and highly skilled qualities of skuas as parasites, they qualify as aposematic species. Aposematism is a condition used by more dangerous/ noxious species to advertise their particular qualities and, thus, ensure the desired response from animals with whom they interact (usually avoidance by predators; reviewed in Pough 1988, Malcolm 1990). In skuas, aposematism may serve as an affective, long-distance signal between conspecifics, which do not parasitize one another (Furness 1987a), thereby preventing lessrewarding interactions between individuals of equal ability, or between kin (see Malcolm 1990). Aposematism might also benefit skuas as a

The relative importance of hatching asynchrony, egg mass and chick growth were studied to establish mass hierarchies in broods of the Black Kite (Milvus migrans). Relative growth of first-hatched chicks was the best predictor of degree of chick mass hierarchy, while the effect of egg mass differences was negligible. A quadratic equation best explained the relationship between hatching asynchrony and growth of first-hatched chicks, probably due to the logistic growth curves in birds. Growth of the first-hatched chicks during the hatching period was not related to weather, breeder experience, brood size or year, but had a slight negative correlation with laying date and a positive correlation with amount of food in nests. Growth of chicks during such a short period in a stage of low energy demand may be little affected by environmental factors.

Seabirds are high trophic predators in marine ecosystems and are sensitive to change in food supply and thus seabirds can be used as monitors of the marine environment. In order to study the foraging responses of Japanese cormorants Phalacrocorax filamentosus breeding at Teuri Island, Hokkaido to changes in fish availability, the diet was assessed from the regurgitations of parents and chicks, and diving behavior was measured by using time‐depth recorders. Breeding performance (brood size, chick growth, breeding success) was monitored using conventional methods to study their breeding responses. Japanese cormorants changed the diet and foraging behavior over four summers. The birds fed mainly on epipelagic schooling fish when they were available and on demersal fish when pelagic fish availability was low. They tended to dive deeper and longer in a year when they fed mainly on demersal fish than the other years, reflecting the change in the depth distribution of prey fish. Chick growth rate did not differ among years, but fledging success was lower in the years of demersal fish as their meal delivery rate was low. When epipelagic schooling fish were considered scare, parents maintained chick growth by reducing brood size. High variability and unpredictability in pelagic fish abundance are key factors affecting the foraging and breeding performance of Japanese cormorants, which could potentially be used to monitor fish resources.

Rapeseed Meal Studies: 5. Effects of (±)-5-Vinyl-2-Oxazolidinethione, a Goitrogen in Rapeseed Meal, on the Rate of Growth and Thyroid Function of Chicks

Bird species adapted to variable environments tend to have slow lean tissue growth rates and high fat deposition rates, allowing survival during food shortages. This emphasis on fat deposition may be a fixed physiological trait. Alternatively, tissue allocation may be adjusted facultatively according to the proximate food supply. We consider two models of facultative adjustment that could account for the emphasis on fat deposition: (1) the fat‐priority model, in which no lean growth occurs when food is scarce, and (2) the lean‐priority model, in which a minimal level of lean growth always occurs but nutrients are otherwise allocated to fat deposition. We tested these two models using Welcome Swallows Hirundo neoxena, a species we show to have a variable food supply that is influenced by weather. We reduced food supply to chicks experimentally, by enlarging broods or excluding parents from chicks, and tested for reduction in wing growth (an indicator of lean growth) and mass growth (an indicator of fat deposition). Mass growth was retarded by both manipulations, but not wing growth, corroborating the lean‐priority model. This growth strategy may function not to cope with violent variation in food supply, but to maintain development and symmetry of wings and feathers in the face of moderate variation in food supply. Our results contrast with those of a similar experiment on the Black Noddy Anous minutus, a species with more severe variation in food supply.

Long-term studies are crucial in ecology, environmental change assessment, resource management and biodiversity conservation. Stercorarius maccormicki (hereinafter – south polar skua) are predators that can threaten populations of bird species of the orders Sphenisciformes and Procellariiformes. At many places in Antarctica, abundance trends for the skua are not known or have not been updated. This study is an attempt to answer the question: how did a south polar skua population react to changes in environmental conditions during 1956–2013? The objectives of the study was (1) to establish the dynamics of the breeding skua population on the Haswell Islands, i.e. Haswell Island and the small islands of the Haswell Archipelago during 1956–2013, and (2) to explain the reasons of the changes in the studied population. A secondary research question was whether there were changes in the spatial distribution of the breeding skua population on the Haswell Archipelago during the study period? The studies have been carried out on the Haswell Archipelago (Davis Sea), mainly in Antarctic Specially Protected Area №127 «Haswell Island and adjacent emperor penguin rookery on fast ice». Ground count was the main method for determining the size of bird colonies. South polar skua bred on 3–8 islands of the Haswell Archipelago. In the study period, the population size of the south polar skua has changed on the Haswell Archipelago. A decrease in the number of individuals (-52%) was observed between 1956–1957 and 1966–1967 breeding seasons. Between 1966–1967 and 1999–2000 breeding seasons, the skua population declined by 30.7% and reached the lowest value of 18 pairs. Population growth (344.4%) was recorded between 1999–2000 and 2009–2010 breeding seasons, with an increase of 33.8% and reaching the maximum value (83 pairs) in 2010–2011 breeding season. By 2012–2013 breeding season, the south polar skua population has declined by 13.2%. On Haswell Island, between 1956–1957 and 2012–2013 breeding seasons, there was a change in skua abundance that was similar to the change in the total breeding population on Haswell Archipelago during the entire period. On the small islands of the Haswell Archipelago, the number of breeding south polar skuas declined (-80%) between 1956–1957 and 1962–1963 breeding seasons. The breeding seasons of 1962–1963, 1966–1967 and 1999–2000 were characterised by the lowest number of individuals. Between 1999–2000 and 2009–2010 breeding seasons, the number of south polar skuas increased by 400%. A decrease in abundance (-41.6%) occurred between 2009–2010 and 2010–2011, followed by the consequent increase (by 36.3%) by 2012–2013 breeding season. During the study period, changes in the abundance of south polar skuas on the Haswell Archipelago were independent of changes in average daily November temperatures between 1956–1957 and 2012–2013 breeding seasons (Mann-Whitney test U = 0, p = 0.0017, n = 7 (asymptotic (2-sided))), when they were laying eggs and heating them. The number of south polar skuas changed independently of changes in the number of individuals of their prey, represented by Aptenodytes forsteri, Pygoscelis adeliae, and Fulmarus glacialoides (respectively U = 49, p = 0.0006, n = 7; U = 16, p = 0.029, n = 4; U = 16, p = 0.029, n = 4 (asymptotic (2-sided))). The high mortality of eggs, chicks and local weather conditions could influence the breeding success of the south polar skua, which could have a delayed effect on their long-term dynamics. Human activities have influenced the skua population, but have not been studied quantitatively. On the Haswell Archipelago, the reasons for historical changes in abundance of the breeding skua population remain largely unclear.

Marine ecosystems face a variety of threats induced by environmental changes and anthropogenic activities. Seabirds are predators often used as indicator species to monitor the status and health of their communities and the environment. Here, we present the results from a 35-year monitoring time series of Brown Skuas (Catharacta antarctica lonnbergi) and South Polar Skuas (C. maccormicki) breeding sympatrically in the Maritime Antarctic on Fildes Peninsula and Potter Peninsula, King George Island. Our results reveal high annual variability in the number and proportions of breeding pairs across the entire study period. Apart from that, the breeding pair numbers of Brown Skuas were relatively stable. By contrast, the breeding pair number of mixed species and South Polar Skua pairs increased substantially until 2003/2004 and 2010/2011, respectively. Both pair types experienced a decline in the breeding pair numbers within recent years. Despite the strong fluctuations in the number of breeding pairs, the sum of occupied territories has been stable during the last 9 years. The breeding success of all pair types declined significantly, and within recent years, both South Polar Skuas and mixed species pairs completely failed to produce offspring. The ultimate causes driving the breeding success decline remain unclear. The overall increase in the number of skuas might have raised density-dependent factors and resulted in a higher predation rate between conspecifics. The more recent total breeding failures, however, indicate a drastic shortage in local food availability.