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Diet and debris ingestion of skuas on Fildes Peninsula, King George Island, Antarctica
Abstract
Using pellet analysis, we characterized the diet and plastic and non-plastic debris ingestion of skuas (Catharacta spp.) during 2017-2020 summer seasons along the coastal sector of Fildes Peninsula (King George Island, Antarctica). In addition, we conducted the same analysis during the 2020 breeding season on reproductive territories of south polar (Catharacta maccormicki) and brown (Catharacta antarctica lonnbergi) skua. Our results confirm the generalist and opportunistic habits of both skua species. Additionally, it has been proposed that brown skua displaces south polar skua from penguin breeding colonies given its higher competitive abilities, and our results suggest this might not have happened during the study period. Along with evidence from other studies, this work underlines the idea that potential local anthropogenic sources of plastic and non-plastic debris at Fildes Peninsula need to be further addressed to improve current mitigation efforts.
... Due to their small size, micro-nano-plastics are readily available to a larger number of species, including marine invertebrates (Ribeiro et al., 2024). Surprisingly, they have been recently reported in Antarctic krill, salps, and whelks, among various benthic invertebrates Sfriso et al., 2020;Wilkie Johnston et al., 2023;Zhu et al., 2023), and animals higher in the Antarctic food chain, such as multiple species of penguins, skuas, and sea lions (Fragão et al., 2021;Le Guen et al., 2020;Leistenschneider et al., 2022;Lenzi et al., 2022). While the toxicity and ecological disruptions that they may induce under realistic concentrations require further investigation, particularly in remote environments like Antarctica, their long-term accumulation remains a matter of concern. ...
In the present study, marine litter in the vicinity of the Machu Picchu Scientific Base, Antarctica, was quantified and characterized. A total of 33 items were counted, primarily composed of plastic debris and foams, followed by metallic structures. A high abundance of marine litter was associated with the proximity to the scientific base. Common plastic polymers were identified by Fourier-transformed infrared spectroscopy, including polypropylene, polyethylene, polyurethane, acrylates, and polystyrene. The abundance of synthetic polymer materials could potentially release toxic chemicals and microplastics into the environment. We suspect that permanent and seasonal Antarctic bases' maintenance and operation release large amounts of structural waste to their surroundings and lack proper solid waste management. For this reason, enforcing solid waste management systems and internal regulations is necessary to follow the guidelines of the Protocol on Environmental Protection to the Antarctic Treaty.
... It is estimated that plastic debris accounts for about 60-80 % of marine litter, reaching as high as 90-95 % in some areas. Plastic debris can be classified according to its size into micro (1 μm-5 mm), meso (5 mm-20 mm) and macro (20 mm-1000 mm) (Barnes et al., 2009;Lenzi et al., 2022;Kibria et al., 2023). Plastic persists in the environment for a long period and some disposable plastic products (water bottles, toothbrushes, fishing lines) can take over 400 years to biodegrade. ...
This review article provides an account of coastal and marine bird species contaminated with plastics in light of
ingestion, taxonomy, feeding clusters, types, shapes, colours and lethal and sublethal effects. Bird species were
found contaminated with plastics in 39 locations/countries across the seven continents. Global analysis shows
that low, medium and high plastic ingestion occurred in bird species across the globe. Fulmars, shearwaters,
petrels, albatrosses, gulls, and kittiwakes (all marine/seabirds) were found contaminated with plastics in several
locations in the world. Bird species belonging to the Procellariidae, Laridae, Diomedeidae (by taxonomy),
piscivorous, molluscivorous, and cancrivorous (by feeding habits) were most contaminated with plastics.
Microplastic, mesoplastic and macroplastic (by sizes), PP, PE, PS, PET, PAN and PVC (by types), fragments,
pellets, fibres, foams, sheets, threads, fishing lines and films (by shapes) and white, blue, green, black, clear, red
and yellow (by colours) were the most common plastics ingested by birds. Several bird species contaminated
with plastics fall within the critically endangered, endangered and vulnerable categories. The ingestion of
plastics can cause direct harm to birds resulting in death. In addition, plastic-derived toxic chemical additives
and plastic-adsorbed toxic chemicals would be an additional stressor causing both lethal and sublethal effects
that can cause greater harm to the health of birds. Several measures are suggested to reduce plastic pollution in
the environment to safeguard birds and the environment
... Their regurgitations have been used to report plastic loads in their seabird prey (e.g. Ryan, 1987;Ryan and Fraser, 1988;Hammer et al., 2016;Ibañez et al., 2020;Lenzi et al., 2022) and to assess temporal variation in plastic amounts and composition in multiple seabird taxa (Ryan, 2008). However, to assess how well regurgitated skua pellets represent what is ingested by their prey, a comparison between the types of plastics collected directly from prey carcasses (stomachs) to those sampled from pellets is still needed. ...
Using seabirds as bioindicators of marine plastic pollution requires an understanding of how the plastic retained in each species compares with that found in their environment. We show that brown skua Catharacta antarctica regurgitated pellets can be used to characterise plastics in four seabird taxa breeding in the central South Atlantic, even though skua pellets might underrepresent the smallest plastic items in their prey. Fregetta storm petrels ingested more thread-like plastics and white-faced storm petrels Pelagodroma marina more industrial pellets than broad-billed prions Pachyptila vittata and great shearwaters Ardenna gravis. Ingested plastic composition (type, colour and polymer) was similar to floating plastics in the region sampled with a 200 μm net, but storm petrels were better indicators of the size of plastics than prions and shearwaters. Given this information , plastics in skua pellets containing the remains of seabirds can be used to track long-term changes in floating marine plastics.
... At a local scale, it avoids direct human intervention on seabird populations and surely has allowed the population stability of skuas in Harmony Point. However, the increased pressure from human-stressors related to the presence of scientific activities [52], debris pollution [53,54], diseases dissemination [55], alien species arriving [56], and climate change [57], are now challenging its effectiveness. ASPAs might not be effective when large-scale processes occur. ...
Regular monitoring of breeding population abundance and environmental factors related to the nesting habitat has proven fundamental for seabird conservation. Harmony Point (Nelson Island) is an Antarctic Specially Protected Area (ASPA) designated to manage and protect the high biological value of seabirds’ richness and abundance. However, due to the remote location of their breeding sites, many species lack updated population counts. Skuas (Catharacta sp.) exhibited a two-decade gap since the last census was conducted in Harmony Point. The abundance and spatial distribution of the nests of skuas were studied during the austral summer of 2019/2020. Through an exhaustive search, we counted and mapped active nests. Nesting habitat was assessed by the use of an unmanned aerial vehicle to take aerial pictures and build an orthomosaic image to determine vegetation in the area. Additionally, a digital elevation model was built to calculate a series of geomorphological-related variables. Suitability models were used to estimate the importance of variables to the nesting of skuas. A total of 71 brown skua (Catharacta antarctica) and 3 south polar skua (C. maccormicki) nests were counted. Two of the seven variables (terrain slope and vegetation cover) accounted for 57.5% ± 14.1% of the models’ variability; sun radiation incidence, and wind shielding were of secondary importance. Water flow accumulation, distance from penguin colonies, and terrain elevation were the least important variables. Skuas selected for nesting flat terrains (slope < 10°) with a vegetation cover of above 20%, slightly higher sun incidence (270 to 280 kW/h), and intermediary windshielding (45% to 55% of exposition). Considering previous estimates, the skua species at Harmony Point has kept an apparently stable population size over the last 25 years. However, expected changes in nesting habitat availability, i.e., increased snow-free area, increased wind intensity, changes in vegetation cover, and reduction of penguin populations, might change population size in the mid to long term.
... The plastic litter entrapped in the patches, mainly ropes, can lead to the entanglement and strangulation of these birds as reported at site 4 and displayed in Fig. 7b. Additionally, various effects of plastic litter on coastal birds have been reported including the entrapment by fishing lines (Battisti et al., 2019), entanglement (Cartraud et al., 2019), ingestion (Lenzi et al., 2022), and the use of plastic in nesting (Massetti et al., 2021). Furthermore, plastic items entrapped in C. maritima patches might cause toxic effects on the coastal fauna in relation with the chemical elements adhered on them or generated after their degradation due to the continuous exposure to abiotic factors (Nakashima et al., 2012;Viñas et al., 2020;Ben-Haddad et al., 2022c;Fajković et al., 2022;Abelouah et al., 2022). ...
Some plant communities of coastal dunes may affect the magnitude and distribution of litter on the ecosystem. In this study, the aim is to assess the aptitude of the halophyte Cakile maritima Scop. 1772 to be a trap and sink of plastic litter on the Moroccan Atlantic coast. Overall, a significant difference was noted between plastic litter trapped in C. maritima patches (1173 items) and control plots (502 items). Food containers and ropes were the most common trapped items. Shoreline and recreational activities, followed by dumping and ocean/waterway activities are the main sources of the trapped plastic items. The findings suggest the expansion of the cleaning operations to include coastal dunes, the need to change behavior among beachgoers in regard to food plastics disposal, as well the control of C. maritima distribution in the study area, and similar plant species in other regions.
Despite the remoteness of the Antarctic continent and Southern Ocean, microplastic (MPs) contamination has been evidenced in recent years. However, the deep-sea compartments of the Southern Ocean are yet to be investigated. In the present study, we conducted a baseline MP assessment of the deep-sea waters and bottom sediments of the Bransfield Strait, Antarctica. A low abundance of suspected MPs was found. The average MP abundances in bottom sediments and water samples were 0.09 MPs/g (range of 0 to 0.2 MPs/g) and 7.00 MPs/L (range of 0 to 16 MPs/L), respectively. The majority of the particles were fibers identified as cellulose, although polyethylene terephthalate (PET) and polyacrylonitrile (PAN) was also detected. These results suggest low MP contamination levels in the Southern Ocean's deepest environmental compartments. However, future studies must aim to investigate the smallest MP fractions and, if possible, nanoplastic (<1 μm) contamination in these remote compartments.
Plastic pollution is a pressing global problem, even in Antarctica and the Southern Ocean, despite their remote and pristine nature. Coming from local sources but also from lower latitudes, the consequences of this pollution, especially of microplastics in Antarctica, are far from being known. The growing evidence of this environmental problem and the growing concern of the Antarctic community has led to a significant increase in research and monitoring initiatives, such as the AntarPLAST Project. While several challenges have been identified for the assessment regarding monitoring and managing plastic and microplastic pollution, possible ways to address them in a collaborative, coordinated, and equitable manner are also envisioned under the newly Antarctic InSync proposal.
Antarctica stands as one of the most isolated and pristine regions on our planet. Regardless, recent studies have evidenced the presence of plastic pollution in Antarctic environments and biota. While these findings are alarming and put into perspective the reach of plastic pollution, it is necessary to assess the current knowledge of plastic pollution in Antarctica. In the present review, an updated literature review of plastic pollution in multiple Antarctic environmental compartments and biota was conducted. Studies were cataloged based on environmental compartments (e.g., sediments, seawater, soil, atmosphere) and biota from different ecological niches. A detailed analysis of the main findings, as well as the flaws and shortcomings across studies, was conducted. In general terms, several studies have shown a lack of adequate sampling and analytical procedures for plastic research (particularly in the case of microplastics) and standard procedures; thus, compromising the reliability of the data reported and comparability across studies. Aiming to guide future studies and highlight research needs, a list of knowledge gaps and recommendations were provided based on the analysis and discussion of the literature and following standardized procedures.
The Arctic and Antarctica represent two of the most inhospitable and poorly investigated biomes in the world. Although polar regions are still perceived as some of the most pristine places still in existence, these remote places are no longer immune to anthropogenic pollution, in particular, micro- and nanoplastics. Seabirds, avian species feeding mainly at sea, are indicators of change in the environment and represent an early study group of ecological indicators for plastic pollution. The goal of this bibliometric overview is to evaluate international research trends on the impacts of microplastics (MPs) and nanoplastics (NPs) on seabirds inhabiting polar regions. A total of at least 13 seabird species were reported to have ingested MPs from 1983–2023. Overall, 1130 samples were investigated, including stomach content, pouch content, guano, and pellets. Pellets were the most investigated substrate (699), followed by stomach contents (309), guano (101), and pouch contents (21). A median of 31.5 MPs per sample was found in the Arctic, with an average of 7.2 MPs per sample. A median of 35 MPs per sample was found in Antarctica, with an average of 1.1 MPs per sample. Overall, MPs were most frequently found in fragment form. A total of 3526 MPs were retrieved from stomachs (3013), pellets (398), guano (75), and pouch contents (40). Polyethylene was the dominant plastic polymer found, followed by polypropylene and polystyrene. The monitoring of MP ingestion is crucial to mitigating the impacts on marine and terrestrial organisms. Standardized protocols could boost the safeguarding of seabirds and reduce the impacts of MPs on polar regions.
Several studies have documented that plastic pollution is affecting one of the most remote and pristine regions of our planet, Antarctica. Plastics of different size and polymeric composition have been retrieved in Antarctic sea ice, surface waters and sediments, with microplastics (mostly fibers) found both in terrestrial and marine organisms. Such evidence raises concerns about potential detrimental effects on biodiversity and ecosystem functions. The present review aims to report the most up-to-date knowledge on occurrence and distribution of plastic pollution in the Antarctic environment and biota including interaction with microorganisms, potential sources, and its impact on Antarctic biota. Our understanding of plastic pollution in this polar region will help us define the human footprint in Antarctica and predict future ecological risks.
South Polar skua (Stercorarius maccormicki) and Brown skua (Stercorarius antarcticus lonnbergi) have opportunistic feeding habits and are the dominant predators in terrestrial Polar regions. These skuas exploit a wide range of food items, including marine organisms, other birds, and even garbage. In the present study, we compare the diets of these two skua species during the breeding season, using pellets and prey remains collected within their territories. The samples were collected at six sites in Admiralty Bay, on King George Island, Antarctica. We identified eight different items, which we classified as “penguin”, “flying bird”, “skua”, “fish”, “gastropod”, “krill”, “egg” and “marine debris”. In the first breeding season (2008/2009), penguins and flying birds were the food resources more abundant for both skua species, and their diet composition was similar. In the second breeding season (2010/2011) South Polar skua exploited more fish and flying birds than Brown skua; the latter exploited more eggs and penguins. Our findings corroborate those of previous studies, demonstrating that in sympatry South Polar skua exploit more fish than Brown skua. The diet of South Polar skua also varied between breeding seasons, reflecting the opportunistic foraging behavior of these skuas. As in other studies, we recorded that skua is a food resource for both skua species, but it was more common in the diet of South Polar skua. Marine debris was recorded only in the samples of Brown skua. Birds are important food items for both skuas, although significant differences were found in the diets of these sympatric species, with shifts in the composition of the diet probably reflecting fluctuations in the abundance of prey populations, which are known to be common at Admiralty Bay, although more data will be needed to confirm this link.
The Antarctic and the surrounding Southern Ocean are currently subject to rapid environmental changes and increasing anthropogenic impacts. Seabird populations often reflect those changes and so act as indicators of environmental variability. Their population trends may provide information on a variety of environmental parameters on the scale of years or decades. We therefore provide long-term data on the cape petrel ( Daption capense ) population from a long-term monitoring program on Fildes Peninsula, South Shetland Islands, Maritime Antarctic, an area of considerable human activity. Our data, covering a period of 36 years, indicate some variability, but no clear trend in the number of breeding pairs between the breeding seasons 1985 and 2006. However, beginning in the 2008 season, the population decreased significantly and reached a minimum in the 2020 season. The mean annual decrease between 2008 and 2020 was 10.6%. We discuss possible causes of this strong negative population trend. Anthropogenic disturbance only affects a few breeding sites in the area and is therefore unable, on its own, to explain the consistent population decline at all the breeding sites studied. We think it more likely that reduced food availability was the main cause of the drastic decline in the cape petrel population.
A mess of plastic
It is not clear what strategies will be most effective in mitigating harm from the global problem of plastic pollution. Borrelle et al. and Lau et al. discuss possible solutions and their impacts. Both groups found that substantial reductions in plastic-waste generation can be made in the coming decades with immediate, concerted, and vigorous action, but even in the best case scenario, huge quantities of plastic will still accumulate in the environment.
Science , this issue p. 1515 , p. 1455
Marine plastic pollution is an environmental contaminant of significant concern. There is a lack of consistency in sample collection and processing that continues to impede meta-analyses and large-scale comparisons across time and space. This is true for most taxa, including seabirds, which are the most studied megafauna group with regards to plastic ingestion research. Consequently, it is difficult to evaluate the impacts and extent of plastic contamination in seabirds fully and accurately, and to make inferences about species for which we have little or no data. We provide a synthesized set of recommendations specific for seabirds and plastic ingestion studies that include best practices in relation to sample collection, processing, and reporting, as well as highlighting some “cross-cutting” methods. We include guidance for how carcasses, regurgitations, and pellets should be handled and treated to prevent cross-contamination, and a discussion of what size class of microplastics can be assessed in each sample type. Although we focus on marine bird samples, we also include standardized techniques to remove sediment and biological material that are generalizable to other taxa. Lastly, metrics and data presentation of ingested plastics are briefly reviewed in the context of seabird studies.
Top predators exhibit a critical role in ecosystem functioning and in the stability of the food web, so research on diet is relevant to understand their foraging behavior. Seasonal variation in diet and prey selection may be the result of fluctuations in the physiological demands during the different annual life cycles, and ecological factors such as resource availability, which may influence the foraging behavior. Moreover, the competition for the feeding territories between conspecifics in a population or with other predators may also lead to diversification of the diet. In this work, we determined the diet of breeding and non-breeding Brown Skuas (Stercorarius antarcticus lonnbergi) at Hope Bay, Antarctic Peninsula, to understand prey selection and the feeding habits of groups with different physiological and energy demands. To assess the breeders’ diet, 204 pellets were collected near the nests, while for non-breeders, 330 pellets were obtained from different areas where they usually group, and prey items were determined. Pellet dimensions were larger in non-breeding skuas. Breeding skuas’ pellets showed a higher content of energy-rich items such as penguin eggs, fishes and molluscs, while in non-breeding skuas, pellets consisted mainly of penguin feathers and bones. The differences in diet between the groups may be a consequence of the supplementation of the food obtained on land by traveling to the ocean by breeding skuas, in order to compensate the energetic demands during reproduction. Our results highlight differences in the feeding habits and prey selection, as well as a variation in the flexibility of the foraging strategy of both groups.
It was thought that the Southern Ocean was relatively free of microplastic contamination; however, recent studies and citizen science projects in the Southern Ocean have reported microplastics in deep-sea sediments and surface waters. Here we reviewed available information on microplastics (including macroplastics as a source of microplastics) in the Southern Ocean. We estimated primary microplastic concentrations from personal care products and laundry, and identified potential sources and routes of transmission into the region. Estimates showed the levels of microplastic pollution released into the region from ships and scientific research stations were likely to be negligible at the scale of the Southern Ocean, but may be significant on a local scale. This was demonstrated by the detection of the first microplastics in shallow benthic sediments close to a number of research stations on King George Island. Furthermore, our predictions of primary microplastic concentrations from local sources were five orders of magnitude lower than levels reported in published sampling surveys (assuming an even dispersal at the ocean surface). Sea surface transfer from lower latitudes may contribute, at an as yet unknown level, to Southern Ocean plastic concentrations. Acknowledging the lack of data describing microplastic origins, concentrations, distribution and impacts in the Southern Ocean, we highlight the urgent need for research, and call for routine, standardised monitoring in the Antarctic marine system.
Plastic pollution has become one of the largest environmental challenges we currently face. The United Nations Environment Program (UNEP) has listed it as a critical problem, comparable to climate change, demonstrating both the scale and degree of the environmental problem. Mortalities due to entanglement
in plastic fishing nets and bags have been reported for marine mammals, turtles and seabirds, and to date over 690 marine species have been reported to ingest plastics. The body of literature documenting plastic ingestion by marine megafauna (i.e. seabirds, turtles, fish and marine mammals) has grown rapidly over the last decade, and it is expected to continue grow as researchers explore the ecological impacts of marine pollution. Unfortunately, a cohesive approach by the scientific community to quantify plastic ingestion by wildlife is lacking, which is now hindering spatial and temporal comparisons between and among species/ organisms. Here, we discuss and propose standardized techniques, approaches and metrics for reporting debris ingestion that are applicable to most large marine vertebrates. As a case study, we examine how the use of standardized methods to report ingested debris in Northern Fulmars (Fulmarus glacialis) has enabled long term and spatial trends in plastic pollution to be studied. Lastly, we outline standardized metric recommendations for reporting ingested plastics in marine megafauna, with the aim to harmonize the data
that are available to facilitate large-scale comparisons and meta-analyses of plastic accumulation in a variety of taxa. If standardized methods are adopted, future plastic ingestion research will be better able to inform questions related to the impacts of plastics across taxonomic, ecosystem and spatial scales.
Many studies have shown that seabirds are sensitive to changes in food supply, and therefore have potential as monitors of fish stocks. For most seabird species breeding parameters suitable for biomonitoring have yet to be measured over a wide range of prey densities. However, it is clear that responses vary among species and care must be taken when interpreting seabird data as a proxy for fish abundance. For many years seabirds have also been used as monitors of pollution, especially oil pollution. Beached bird surveys provide important evidence of geographical and temporal patterns, and, for example, show consistent declines in oil release into the southern North Sea over the last 15 years. Analysis of oil on birds can now permit fingerprinting of sources, allowing prosecution of polluters. As predators high in marine food webs, seabirds also have potential as monitors of pollutants that accumulate at trophic levels. Recent work on mercury in seabirds has permitted an analysis of spatial patterns and of the rates of increase in mercury contamination of ecosystems over the last 150 years, since mercury concentrations in feathers of museum specimens can be used to assess contamination in the birds when they were alive. Surprisingly, pelagic seabirds show higher increases than most coastal ones, and increases have been greatest in seabirds feeding on mesopelagic prey. This seems to relate to patterns of methylation of mercury in low-oxygen, deeper water. Accurate measurement of long-term trends in mercury contamination depend on the assumption that seabird diet composition has not changed. This can be assessed by analysis of stable isotopes of N and C from the same feathers used for mercury measurement, a technique that also permits the monitoring of trophic status over time or between regions. While high mercury contamination of seabirds in the southern North Sea is unsurprising, we cannot yet explain certain unexpected results, such as high levels in seabirds from north Iceland compared with those from south Iceland or Scotland.
Understanding seabird marine habitat affinities, at-sea behavior, variability in reproductive success, migratory patterns, phenology, and other life history traits depends primarily on knowledge of the prey that they consume. Traditionally, estimating diets has been done through classification and enumeration of prey remains found in stomach contents of seabirds collected at sea, as well as chick meals, pellets, and feces collected at breeding colonies. These techniques have the advantage of high taxonomic resolution of prey, but suffer from biases due to the underestimation of soft-bodied or small prey that are digested completely and overestimation of prey with durable parts that are retained for long periods of time. Recent innovations in 2 biochemical assays of seabird tissues-stable isotope and fatty acid analyses-have greatly expanded knowledge of seabird diets and have advanced our understanding of the ways in which seabirds can indicate inter-seasonal, annual, decadal, and longer shifts in oceanographic conditions over varying spatial scales. Advances in statistical approaches to these data have provided new ways in which prey can be identified and quantified. When applied in combination, these 3 techniques (traditional diet sampling, and stable isotope and fatty acid analyses) have the potential to reveal pathways of energy flux across marine ecosystems and to provide new insight into marine ecosystem dynamics. We review the basic principles of these approaches to determining seabird diet and emphasize the need for more formal conceptual and statistical integration of methods to advance this field.
Patterns of intraspecific variability of ingested plastic loads in seabirds were examined for species collected off southern Africa. The incidence of plastic pollution was shown to be increasing during the 1980s. Both large-and small-scale geographic variation in plastic loads occurred as a function of variable plastic density in the environment. In-tergenerational transfer of plastic particles was identified as an important pathway for plastic flow in those species that accumulate plastic particles and feed their chicks by regurgitation. This pathway can account for higher plastic loads in nonbreeders and failed breeders than in birds that breed successfully, and such results need not indicate adverse effects from plastic ingestion. Intergenerational transfer resulted in annual cycling of plastic loads in successfully breeding birds. In species that do not regurgitate indigestible stomach contents, immature birds have the largest plastic loads and are most likely to exhibit adverse effects from plastic ingestion.
The diets of Southern Hemisphere skuas Catharacta sp. are reviewed. Data from 189 sources were analyzed and are separately presented for the breeding and non-breeding season, and for eight different regions: (1) Tierra del Fuego, (2) the Falkland Islands, (3) South Georgia, (4) the Tristan da Cunha and Gough Island group, (5) the Antarctic Peninsula, the South Shetland and South Orkney Islands, (6) the continental coast of Antarctica, (7) the Prince Edward, Crozet, Kerguelen and Heard Island groups, and (8) Macquarie Island, the Chatham, Antipodes and Snares Islands, according to both taxonomy and the main distribution areas. We furthermore present the mode of foraging employed by skuas as well as the method of sampling by the observer. Semi-quantitative investigations have been carried out in only 12 studies. A total of 110 food items has been identified to species level.
The food provided to South Polar Skuas (Stercorarius maccormicki) chicks was determined at two Antarctic sites where South Polar Skuas breed sympatrically with Brown Skuas (S. antarcticus). At Harmony Point on Nelson Island, 16 samples of regurgitated stomach contents were analyzed, all contained remains of penguin chicks (mostly soft tissues), which constituted the bulk of the contents, while only two samples had fish or krill remains. These South Polar Skuas had access to penguin colonies, where they hunted chicks or fed on fresh carcasses. However, at Half Moon Island, only two out of nine samples contained minor amounts of penguin remains while fish were the major dietary resource. The high fish content in their diet may indicate a preference for marine rather than terrestrial resources or be the result of competition with Brown Skuas. The variability in food items evidenced by the differences in regurgitated stomach contents indicates that South Polar Skuas may have a trophic plasticity that allows them to change their feeding habits from one resource to another one according to availability. Such may make them less vulnerable to a reduction in the availability of a particular food item.
We synthesize the available literature on marine debris and its impacts in the sub-Antarctic islands, the
Antarctic Peninsula and on the coasts of Antarctica. A total of 98 documents covering reports from 1982 to
2010 were included, and of these 95% had their full contents accessed. Seventy documents were obtained
online as scientific abstracts from the Commission on the Conservation of Antarctic Marine Living Resources
(CCAMLR). The occurrence of marine debris in the Antarctic environment, fur seal entanglement in marine
debris, interactions between seabirds and marine debris and long range transport of benthos on floating plastics were the main issues identified. Fishing operations in the Southern Ocean were identified as the major source of marine debris, but depending on the type of debris reported, plastics from lower latitudes may also cross the Polar Front (PF). Possible links between Antarctic and South America, the closest intercontinental connection, in relation to plastic marine debris pollution are highlighted. As reported at lower latitudes, plastic pollution is an important problem now challenging the Antarctic environment. However, further specific and detailed studies are vital, since our current level of knowledge probably exposes only a small part of the full problem - the tip of iceberg.
Since the inception of the Antarctic Treaty, numerous regulations for environmental protection were adopted by the Treaty parties to minimise negative environmental impacts of human activity. Nevertheless, the concentration of a variety of human activities in some Antarctic regions leads to a conflict of interest. The Fildes Peninsula on King George Island, in the Antarctic Peninsula, represents a unique example of increasing human pressure due to multiple human uses. Scientific research, station operations, transport logistics, tourism, nature conservation and protection of geological and historical values regularly overlap in space and time. A standardised assessment of fauna, flora and impact of human activities on the terrestrial ecosystem was conducted between 2003–2006 and 2008–2011 to provide a comprehensive dataset that documents the environmental state of the Fildes Peninsula. Management measures are suggested to mitigate these impacts, such as the designation of an Antarctic Specially Managed Area. The political debate amongst the Treaty parties about regulatory measures is on-going, but we strongly recommend immediate action.
The Antarctic terrestrial environment is under increasing pressure from human activities. The Fildes Region is characterized by high biodiversity, but is also a major logistic centre for the northern Antarctic Peninsula. Different interests, from scientific research, nature conservation, protection of geological and historical values, station operations, transport logistics and tourism, regularly overlap in space and time. This has led to increasing conflict among the multiple uses of the region and breaches of the legal requirements for environmental protection that apply in the area. The aim of this study was to assess the impacts of human activities in the Fildes Region by monitoring the distribution of bird and seal breeding sites and recording human activities and their associated environmental impacts. Data from an initial monitoring period 2003-06 were compared with data from 2008-10. We observed similar or increased levels of air, land and ship traffic, but fewer violations of overflight limits near Antarctic Specially Protected Area No. 150 Ardley Island. Open waste dumping and oil contamination are still major environmental impacts. Scientific and outdoor leisure activities undertaken by station personnel are more frequent than tourist activities and are likely to have a commensurate level of environmental impact. Despite the initial success of some existing management measures, it is essential that scientific and environmental values continue to be safeguarded, otherwise environmental impacts will increase and the habitat will be further degraded. We argue that the Fildes Region should be considered for designation as an Antarctic Specially Managed Area, a measure that has proven effective for environmental management of vulnerable areas of the Antarctic.
It is broadly accepted that the brown skua (Stercorarius antarcticus lonnbergi) competitively excludes the south polar skua (S. maccormicki) from penguin colonies when breeding sympatrically, forcing the latter to feed on marine resources. The purpose of this work
was to examine the diets and trophic niche breadths of each species where they co-occur and to determine the degree of overlap.
To this end, we analyzed 169 pellets of brown skuas, collected in two different areas (20 individuals), and 152 of south polar
skuas, collected in three different areas (18 individuals), on Deception Island, South Shetland Islands, Antarctica, during
the austral summer 2000. Pellet analysis often underestimates the amount of easily digestible prey, but allows for comparisons
of the relative contributions of different items in the diet. South polar skuas at our study locations consumed seven different
food items and had a trophic niche breadth of 0.133 compared to brown skuas that fed on 10 different items and had a trophic
niche breadth of 0.078. The niche overlap between the species was 82.1%. Penguins were the principal food source of both species,
however, brown skuas fed mostly on chicks, while south polar skuas fed on adults (carcasses). The use of different age classes
of penguins as a food source offers an alternative to competitive exclusion, allowing the coexistence of these species on
Deception Island.
During thirty three expeditions to the Polish Arctowski Antarctic Station signifi− cant influences of human activity upon the environment have been recorded. Introductions of alien species, shifts of bird and seal breeding areas and decreases in both bird and seal populations, are the most obvious effects of human pressure. Though numbers of visits by tourists have increased during this period, impacts from expeditioners appear to be the main cause of changes. In particular, increasing numbers and mobility of summer groups at the station are the likely most influential factors.
South Polar skuas (Catharacta maccormicki) breed on Ardery Island in the absence of a local breeding population of Adelie penguins (Pygoscelis adeliae). Assessment was made of the food remains in skua feeding territories in 1995/1996. The diet of South Polar skuas largely
consisted of fulmarine petrel species which bred on Ardery Island. Southern fulmar (Fulmarus glacialoides) remains were the predominant prey items found, and skuas appeared to feed preferentially on this species.
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.
South polar skuas, SPS, (Catharacta maccormicki) and brown skuas, BS, (C. antarctica lonnbergi) are regarded as opportunistic predators. When breeding in sympatry, BS feed mainly on penguin eggs and chicks, while SPS forage almost exclusively at sea. The objective of this study was to determine the diet composition of adult SPS and BS breeding in sympatry, in order to assess food resource partitioning between these species. The total number of food items consumed was 375 for BS and 682 for SPS in 1992–93, and 427 for BS and 579 for SPS in 1995–96. The pellets composition was significantly correlated between skua species for the same breeding season (r
s = 0.67, p = 0.0062 and r
s = 0.81, p < 0.001, for 1992–93 and 1995–96, respectively), and between breeding seasons for the same skua species (r
s = 0.71, p = 0.001 and r
s = 0.81, p < 0.001, for SPS and BS, respectively). Trophic niche breadth of BS was wider than that of SPS (B
A(BS) = 0.28 and B
A(SPS) = 0.24; Z = 7.67; p < 0.001). The trophic niche overlap between BS and SPS was over 65% in both breeding seasons. In agreement with other studies on the diet of these skua species in situations of sympatry, SPS consumed more fish and BS consumed more birds.
Over the last three decades, many studies have attempted to explain forager diets by using optimal diet theory (ODT). Despite some obvious successes, the utility of this theory remains controversial. We reviewed the results of 134 studies of optimal diet theory to test hypotheses on factors that can explain variation in the ability of ODT to predict diets and diet shifts in response to changes in prey availability. Our major conclusion is that while ODT has generally worked well for foragers that feed on immobile prey, the theory often failed to predict the diets of foragers that attack mobile prey. We found only mixed support for the hypothesis that the theory works better when the study scenario more closely fits the assumptions of the model. Contrary to our a priori predictions, forager types (invertebrate versus ectothermic vertebrate versus endothermic vertebrate) did not differ in their likelihood of corroborating ODT. Two explanations for why optimal diet theory does not work well with mobile prey are that studies on mobile prey often lack information on key parameters that are required to rigorously test ODT, and that with mobile prey, variations among prey in vulnerability (encounter rate and capture success) are often more important than variation in predator active choice in determining predator diets.
Barrett, R. T., Camphuysen, C. J., Anker-Nilssen, T., Chardine, J. W., Furness, R. W., Garthe, S., Hüppop, O., Leopold, M.
F., Montevecchi, W. A., and Veit, R. R. 2007. Diet studies of seabirds: a review and recommendations. – ICES Journal of Marine
Science, 64.
We review the different methods that are used to collect dietary data from marine birds. We consider their limitations and
practicalities and emphasize critical data gaps in our knowledge of the feeding ecology of seabirds (na mely diets outside
breeding seasons). To enhance comparability of findings among studies, species, and oceanographic regions, we make recommendations
on standards for the reporting of results in the literature.
Plastic and microplastic debris is transported by ocean currents over long distances, reaching remote areas, far from its original source. In Polar Regions, microplastics (MPs) can come from local activities or be transported from lower latitudes, with the former being the likely and major source. Although historically Antarctica was considered isolated from the global ocean, there is recent evidence of materials and organisms being transported in and out of the Southern Ocean, despite its multi-front structure. During the austral summer of 2019, beach surveys were conducted on the NW coast of the Fildes Peninsula (King George Island). The beach was characterised, and the first 2 cm of sediment from 5 quadrants (50 × 50 cm) along 100 m of the highest strandline were collected. Large microplastics (LMPs) and mesoplastics (MesoPs) were isolated, counted, measured, weighed and classified by shape. Polymer composition was analysed by FTIR and ageing estimated by Carbonyl Index. We found 293 items of LMPs (188 items) and MesoPs (105 items), with a total average density (±SD) of 234.4 ± 166 items m-2. Foams (130.4 ± 76.3), fragments (58.4 ± 56.0) and pellets (44.0 ± 50.5) were the most abundant shapes. The main polymers found were polystyrene, polypropylene, and polyethylene. We found pellets among the MesoPs, being the first record for beaches in Antarctica. The presence of these primary MPs south of 62°S not only alerts about their possible direct consequences on Antarctic ecosystems, but also gives empirical evidence for the passive entry of plastic debris from lower latitudes through cross-frontal exchanges, providing new evidence of a global connectivity of the Southern Ocean. Despite increasing research, knowledge of plastics dynamics and their impact in the Southern Ocean and Antarctica is still limited but certainly necessary.
Resource acquisition and allocation impacts individual fitness. Using pellet analysis of breeding adults and stable isotopes of carbon and nitrogen of down feathers of Kelp Gull (Larus dominicanus) nestlings, we evaluated the relationship between urban refuse (beef and chicken) and natural food (fish) consumption of individual females during the pre-incubation period, with fecundity and young nesting's success in the Río de la Plata Estuary in Uruguay. Assimilated urban refuse positively correlated with egg weight and negatively with young nestling's success. This suggests a possible impact of urban refuse foraged by females during the pre-incubation period on their immediate fecundity (positively) and young nestling's survival (negatively). Differences between studies at the individual and colony levels are also discussed in light of an "ecological fallacy" of interpretation and we thus argue for the need of additional research to evaluate this relationship further, considering potential confounding factors.
Drastic sea ice retreats in the Antarctic Peninsula, and the consequent environmental changes have brought about the consequences of biological adaptation and food competition. The isotopic niche is reflected by the ecological position and functional role of a species, which can be altered depending on these environmental changes. We assessed the isotopic niche and trophic positions (TP) of 3 seabirds on the Barton Peninsula, King George Island, Antarctica, to understand ecological interaction among the species. The average TP of Antarctic krill (Euphausia superba) (hereafter “krill”) (2.6 ± 0.1) was estimated by using the compiled published data of the compound-specific nitrogen isotope ratio of glutamic acid and phenylalanine in the Southern Ocean, and TP values of the seabirds based on that of krill to be reliable according to ecological knowledge. Our results on the overlap of the isotopic niches of seabirds suggests potential diet competition among the consumers, such as the brown skua (Stercorarius antarcticus) and south polar skua (Stercorarius maccormicki), whereas the distinct and broad isotopic niche width of kelp gulls (Larus dominicanus) suggesting that their adaptation through generalization was related to their extended habitat and various food sources. Our research indicates that isotopic niche of seabirds reflects their survival strategy for food competition. Consequently, these seabirds can be easily influenced by alternative food sources, including terrestrial and human-derived sources, by rapid environmental changes, indicating that they are valuable as key environmental species and require long-term monitoring in the Antarctic Peninsula.
Antarctica, an area that is devoted to global peace and research, is being challenged by climate change, human activities, and pollution. There have been a number of studies concerning the state of the Antarctic ecological environment. However, a comprehensive and quantitative assessment of the impact of threats on the Antarctica ecological environment is still lacking. In this study, a cumulative impact assessment performed on the basis of expert judgement was used to estimate species-specific differences on the impact of seven threats: climate change, organic and nonorganic pollutants, station construction, power generation, oil spilling, and tourism. The terrestrial area of the Fildes Peninsula was divided into 103 cells using a raster grid of 0.25 km², and cumulative impact assessment was applied to each cell. The analysis results indicated that cumulative impact scores (IC) ranged from 0 to 39.4, and the cumulative scores were divided into six categories ranging from very low impact (IC ≤ 7.08) to very high impact (IC > 20.54). More than half of the terrestrial area (57.3%) experienced “Very Low Impact” or “Low impact” scores. For single factors, climate change was identified as a rapidly growing and significant threat facing the terrestrial ecosystems of Antarctica. In addition, tourism had the greatest impact among all human activities. The analytical process and resulting map indicate that it is necessary to develop international policies on the restriction of tourist activity space and strength the organic pollutant controls for terrestrial ecosystem protection in the Fildes Peninsula, Antarctica.
During the last decades plastic pollution has become a common issue in marine environments. Studies on seabirds have focused on species that ingest plastics mistaken for prey or indirectly through their preferred prey or, on how foraging strategy influences this behaviour. We evaluated plastic ingestion in relation to the proximity of nests to areas with different anthropogenic pressure, breeding status and breeding stage. We analyzed regurgitated pellets (n = 1001) from a seabird, the Brown Skua (Stercorarius antarcticus lonnbergi) at Esperanza/Hope Bay, Antarctic Peninsula. Plastics were found in 9% of pellets, only in breeders from an area with high antropogenic activity. The prevalence of plastic increased during the brooding of chicks stage, when skuas expand their feeding niche. Our results support previous work which demonstrated that seabirds with wider feeding niche show higher loads of plastics. Altogether, this provides insights into the dynamics of plastic transfer within the environment.
In the last decade many studies have described the ingestion of plastic in marine animals. While most studies were dedicated to understanding the pre-ingestion processes involving decision-making foraging choices based on visual and olfactory cues of animals, our knowledge in the post-ingestion consequences remains limited. Here we proposed a theoretical complementary view of post-ingestion consequences, attempting to connect plastic ingestion with plastic-induced satiety. We analyzed data of plastic ingestion and dietary information of 223 immature green turtles (Chelonia mydas) from tropical Brazilian reefs in order to understand the impacts of plastic ingestion on foraging behavior. Generalized linear mixing models and permutational analysis of variance suggested that plastic accumulations in esophagus, stomach and intestine differed in their impact on green turtle's food intake. At the initial stages of plastic ingestion, where the plastic still in the stomach, an increase in food intake was observed. The accumulation of plastic in the gastrointestinal tract can reduce food intake likely leading to plastic-induced satiety. Our results also suggest that higher amounts of plastics in the gastrointestinal tract may led to underweight and emaciated turtles. We hope that adopting and refining our proposed framework will help to clarify the post-ingestion consequences of plastic ingestion in wildlife.
Little attention has been drawn toward the effects of marine debris ingestion in relation to nutrient acquisition and fitness consequences. We tested whether anthropogenic debris ingestion influence the nutritional niches of endangered green turtles (Chelonia mydas) in estuarine and reef habitats on the Brazilian coast. Our results showed that estuarine turtles consumed diets with lower proportional wet mass composition of protein (P) and water (W) than their reef conspecifics. The amounts of debris, mostly plastics, retrieved from the digestive tracts of estuarine turtles were higher compared with those individuals from reefs. The realized nutritional niche from estuarine turtles was subject to the debris density in the environment, lack of benthic food resources available and the surface foraging behavior, likely preventing them from reaching their nutritional goals and resulting in lower fitness. The study provides critical information for the management and conservation of ecologically threatened individuals, populations, and their natural habitats.
To access pdf: https://authors.elsevier.com/a/1aX9t,ashxl5A
Although the perils of plastics to living organisms including humans have been neglected for decades, they have recently been recognized as a major environmental problem worldwide. Little progress has been made on understanding the factors that drive species' and populations' susceptibilities to the ingestion of plastic. Here, we propose using nutritional ecology as a multidisciplinary framework for bridging the gaps that link nutrition, behavior, plastics, physiology and ecology. We show that nutritional niches are tightly linked to plastic ingestion, illustrating the application of our framework in the context of nutritional niche theory, habitat-specific foraging from species to populations, and transfer patterns in food webs.
We observed that South Polar Skuas (Catharacta maccormicki) breeding near the Adélie Penguin (Pygoscelis adeliae) western colony at Cape Crozier, Ross Island, Antarctica were able to forage throughout the colony, the majority of which was not defended by territorial skuas as in other Ross Island colonies. All local skuas were able to find enough food on the colony throughout January to support breeding and none were seen to forage at sea. Skuas foraged as individuals to obtain penguin eggs and chicks but kleptoparasitism usually occurred so that several skuas fed in turn on a single carcass. At the end of each feeding event a general melee occurred in which up to 30 skuas fought over the chick remains. The implications for skua breeding of this foraging regime, in which any skuas in the local area can obtain penguin food, are considered. We suggest that the high levels of food availability contributed to the unusually high success for this region of these skuas in raising both chicks. Desertion of chicks while foraging, however, leads to some mortality among older chicks later in the season through predation. It is recommended that further research on skuas at super-large penguin colonies be undertaken.
Plastic debris in the marine environment is widely documented, but the quantity of plastic entering the ocean from waste generated on land is unknown. By linking worldwide data on solid waste, population density, and economic status, we estimated the mass of land-based plastic waste entering the ocean. We calculate that 275 million metric tons (MT) of plastic waste was generated in 192 coastal countries in 2010, with 4.8 to 12.7 million MT entering the ocean. Population size and the quality of waste management systems largely determine which countries contribute the greatest mass of uncaptured waste available to become plastic marine debris. Without waste management infrastructure improvements, the cumulative quantity of plastic waste available to enter the ocean from land is predicted to increase by an order of magnitude by 2025.
Copyright © 2015, American Association for the Advancement of Science.
Human activities are the main current driver of global change. From hunter-gatherers through to Neolithic societies-and particularly in contemporary industrialised countries-humans have (voluntarily or involuntarily) provided other animals with food, often with a high spatio-temporal predictability. Nowadays, as much as 30-40% of all food produced in Earth is wasted. We argue here that predictable anthropogenic food subsidies (PAFS) provided historically by humans to animals has shaped many communities and ecosystems as we see them nowadays. PAFS improve individual fitness triggering population increases of opportunistic species, which may affect communities, food webs and ecosystems by altering processes such as competition, predator-prey interactions and nutrient transfer between biotopes and ecosystems. We also show that PAFS decrease temporal population variability, increase resilience of opportunistic species and reduce community diversity. Recent environmental policies, such as the regulation of dumps or the ban of fishing discards, constitute natural experiments that should improve our understanding of the role of food supply in a range of ecological and evolutionary processes at the ecosystem level. Comparison of subsidised and non-subsidised ecosystems can help predict changes in diversity and the related ecosystem services that have suffered the impact of other global change agents.
Many studies have shown that seabirds are sensitive to changes in food supply, and therefore have potential as monitors of fish stocks. For most seabird species breeding parameters suitable for biomonitoring have yet to be measured over a wide range of prey densities. However, it is clear that responses vary among species and care must be taken when interpreting seabird data as a proxy for fish abundance. For many years seabirds have also been used as monitors of pollution, especially oil pollution. Beached bird surveys provide important evidence of geographical and temporal patterns, and, for example, show consistent declines in oil release into the southern North Sea over the last 15 years. Analysis of oil on birds can now permit fingerprinting of sources, allowing prosecution of polluters. As predators high in marine food webs, seabirds also have potential as monitors of pollutants that accumulate at trophic levels. Recent work on mercury in seabirds has permitted an analysis of spatial patterns and of the rates of increase in mercury contamination of ecosystems over the last 150 years, since mercury concentrations in feathers of museum specimens can be used to assess contamination in the birds when they were alive. Surprisingly, pelagic seabirds show higher increases than most coastal ones, and increases have been greatest in seabirds feeding on mesopelagic prey. This seems to relate to patterns of methylation of mercury in low-oxygen, deeper water. Accurate measurement of long-term trends in mercury contamination depend on the assumption that seabird diet composition has not changed. This can be assessed by analysis of stable isotopes of N and C from the same feathers used for mercury measurement, a technique that also permits the monitoring of trophic status over time or between regions. While high mercury contamination of seabirds in the southern North Sea is unsurprising, we cannot yet explain certain unexpected results, such as high levels in seabirds from north Iceland compared with those from south Iceland or Scotland.
King George Island, largest of the South Shetland Islands, is the site of nine scientific stations of different nationalities operating within the Antarctic Treaty System. Following a recent visit by the author to assess environmental and management issues, this article (the first of two) updates the status of developments on the island and outlines problems, real and potential.which have arisen from scientific activities, tourism, vehicles, use of fuels and waste disposal. It is concluded that existing management practices have not been adequate to deal with these problems and new approaches are required.
Great skuas on Foula, Shetland have responded to a decline in the availability of sandeels since the late 1970s by increasing the proportion of other items in their diets. This change is correlated with the annual recruitment of sandeels in Shetland waters. Since 1983 there has been a 10-fold increase in predation by great skuas upon other seabirds, as Furness & Hislop (1981) suggested might occur in response to a low availability of sandeels. Changes in diet have been accompanied by a 50% reduction in adult territorial attendance as adults increased their foraging effort, such that between 1987 and 1989 breeding adults were probably working as hard as they were able to. Despite this, breeding success was less than 40% in 1987 and less than 15% in 1988 and 1989. The major cause of breeding failure was predation of unguarded chicks by adults from neighbouring territories. The willingness of adults to expose their chicks to high predation risk is probably maintained because of a positive correlation between chick pre-fledging growth and post-fledging survival, which is expressed up to the age of two years and which will place a strong pressure upon adults to feed their chicks as well as possible. The high expenditure of effort by adults in 1987 and 1988 did not affect the weights of those birds incubating eggs in 1988 and 1989, but there was a slight (3%) decrease in egg size between the late 1970s and the late 1980s. Changes in the age structure of the breeding population and the absence in 1989 of 28% of adults colour-ringed during incubation in 1988 suggest an increase in the rate of egress since the 1970s. These changes probably represent an increase in the long-term costs of reproduction to adults at this colony.
Seabirds’ behavioural activity budgets have been proposed as an indicator of changes in marine food supplies. Reduced recruitment and a low biomass of sandeels Ammodytes spp. around Shetland in the late 1980s were associated with a dramatic increase in the foraging effort of breeding skuas. We present data on the territorial attendance patterns of breeding Great Skuas Catharacta skua and Arctic Skuas Stercorarius parasiticus in Shetland in 1987 and examine three aspects of the recorded increase in foraging effort.
Time budget studies indicate that recording territorial attendance by infrequent, daily spot observations provides an accurate measure of the time spent off‐territory by both skua species. None of the pairs of Arctic Skua studied ever left their chicks unattended in 1987. The same was true of 10 out of 27 pairs of Great Skuas. Although the remaining pairs of Great Skuas frequently left their chicks unprotected, evidence of pair co‐ordination to minimise this suggests that their foraging schedules were still constrained by the need to protect their offspring. During periods of high chick‐demand, variation between pairs’ foraging efforts largely reflected variation in those of the females. Thus, we suggest that increased chick neglect in years of food shortage arises as females abandon their role of guardian for that of provider. By the end of the breeding season in 1987, both male and female Great Skuas foraged from 65 to 89% of daylight hours. The lack of any further increase in the foraging effort of Great Skuas in subsequent years of poorer reproductive success was almost certainly because time and energy constraints prevented either sex from doing so. We suggest that the comparatively short amount of time spent foraging by Arctic Skuas in 1987 may reflect an advantage conferred by their role as specialist kleptoparasites.
The diet of the brown skua (Catharacta skua lönnbergi) was studied at Mayes Island, Kerguelen archipelago, by collection of prey remains on 11 territories during the complete breeding cycle of the species there. In nine territories, collections were daily or every two days for a quantitative investigation of the diet. The blue petrel (Halobaena caerulea) and thin-billed prion (Pachyptila belcheri) accounted for, respectively, 72.9 and 19% of the remains. Differences in diet and prey capture rate were analysed according to territory size, local abundance of prey inferred from the vegetation cover of territories, colony attendance patterns of prey, and according to the breeding timing and success of skuas. Skuas holding large territories caught more prey, and especially more blue petrels than those with small territories. Diet reflected local abundance of blue petrel and thin-billed prion but the blue petrel was apparently preferred to other available prey. Failure to breed was not significantly related to hunting performance of the skua or to food availability, but sample size was small. Variations over time of prey capture rates reflected the colony attendance patterns of the main prey. Captures of blue petrel and thin-billed prion were most numerous during their respective laying, incubation and hatching periods, decreasing during chick-rearing. Prey capture rates were greatest when brown skuas were hatching, and decreased during chick-rearing to a minimum when young skuas were fledged. Capture rate patterns differed according to laying date of skuas: early breeding skuas caught more prey and were well synchronized with the breeding cycle of the blue petrel and late breeders exhibited more dependence on the thin-billed prion for some periods. Finally, this study has allowed us to assess the impact of the brown skuas upon the burrowing petrels on this locality.
Regurgitated pellets and food remains were collected near nest sites, and from a club site, of south polar skuas Catharacta maccormicki in the eastern Larsemann Hills, Princess Elizabeth Land, East Antarctica, during the skuas' presence in the area. The samples indicated that the snow petrel Pagodroma nivea, the most abundant seabird species breeding locally, formed the major dietary component, comprising some 66% of food items identified in pellets and 80% of the food remains obtained. Adlie penguins Pygoscelis adeliae (which do not breed in the Larsemann Hills), other seabirds, fish and marine foods were rarely found as remains or in pellets. However, refuse (meat, fish and vegetable remains) taken as food by skuas from nearby stations occurred in pellets at all sites and formed about 12% of the food remains collected and identified. In this study, foods taken by skuas were related both to the local breeding distribution of snow petrels, and to the possession of a feeding territory. Birds without feeding territories took somewhat fewer snow petrels and included more refuse from local stations in their diet, as did those at the club site. Future monitoring of the influence of anthropogenic foods (and inedible waste materials) on the species' ecology is considered important.
Pellets regurgitated by south polar skuas at Hop Island, in the Rauer Group, East Antarctica, Princess Elizabeth Land were collected and analysed. Individual collections were grouped in relation to the nearest breeding colony of seabirds, but irrespective of their source the frequencies of occurrence of the food items identified in pellets indicated that Adlie penguins were of varying, but major (29%–72%), importance to skuas inhabiting the Island. Though the incidence of Antarctic petrel remains (from adult or chick) was generally low in pellets (27%) at all sites near the fulmar breeding colonies. Fish remains, and beaks of cephalopods, were present in few pellets. Whilst indicating the range of foods eaten on Hop Island, and perhaps their relative importance, it is considered that the pellets by themselves do not reflect accurately the level of predation of eggs of Antarctic petrels and southern fulmars, nor do the pellets necessarily include the remains of young of these species.
Regurgitated pellets and fecal samples from south polar skuas Catharacta maccormicki breeding on Ross Island were analyzed for diet items. Adult penguin feathers were found in 79% of all the pellets and 42% of the fecal samples. Evidence of fish was found in 26% of the pellets and 39% of the fecal samples. The amount of refuse in the diet of skuas on Ross Island was directly related to the distance from McMurdo Station.
Regurgitated boluses of undigested material were examined from six sites in East Antarctica. Skuas nesting near Adelie penguin, southern fulmar and Antarctic petrel colonies showed greater site fidelity in their feeding than did skuas nesting close to cape petrels or a Weddell seal pupping site.