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Robert W Furness - One of the best experts on this subject based on the ideXlab platform.
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change in the north sea ecosystem from the 1970s to the 2010s great Skua diets reflect changing forage fish seabirds and fisheries
Ices Journal of Marine Science, 2019Co-Authors: Gabriella E Church, Robert W Furness, Glen Tyler, Lucy Gilbert, Stephen C VotierAbstract:Understanding anthropogenic impacts are crucial to maintain marine ecosystem health. The North Sea has changed in recent decades, largely due to commercial fishing and climate change. Seabirds can act as useful indicators of these changes. By analyzing n = 20 013 pellets and n = 24 993 otoliths regurgitated by great Skuas Stercorarius Skua in northern Scotland over five decades from the 1970s to the 2010s (in 36 years 1973–2017), we reveal how the diet of this top predator has changed alongside the changing North Sea ecosystem. Sandeels Ammodytes spp. were the most common dietary item during the 1970s, but became virtually absent from the 1980s onward. Discarded whitefish dominated Skua diets from the 1980s to the present day, despite long-term declines in North Sea discard production. However, the discarded fish eaten by great Skuas has become smaller and the species composition changed. Skua pellets only rarely contained avian prey in the 1970s but this increased during the 1980s, and fluctuated between 10% and 20% from the 1990s to 2010s. There have also been changes in the avian prey in the diet—black-legged kittiwakes Rissa tridactyla generally being replaced by auks Alcid spp. and northern fulmars Fulmarus glacialis. The Shetland marine ecosystem has experienced steep declines in sandeel stocks and in seabirds that feed on them. Great Skuas have been able to prey switch to respond to this change, supported by abundant discards, enabling them to maintain a favourable population status while other seabird species have declined.
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the effect of long range transport trophic position and diet specialization on legacy contaminant occurrence in great Skuas stercorarius Skua breeding across the northeast atlantic
Environmental Pollution, 2019Co-Authors: Eliza H K Leat, Robert W Furness, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Tor Harry Bjorn, Geir W Gabrielsen, Jan Ove Bustnes, Ane HaarrAbstract:Abstract High levels of halogenated organic contaminants (HOCs) have been found in the marine predatory seabird great Skua (Stercorarius Skua) from breeding colonies in the Northeastern Atlantic, with large unexplained inter-colony variation. The present study aimed at analyzing if the HOCs occurrence in breeding great Skuas in remote colonies was explained by local baseline food web exposure determined by long-range transport, or by ecological factors such as diet specialization and relative trophic position in the breeding area. The occurrence of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) was analyzed in plasma of 204 adult great Skuas collected over two years (2008 and 2009) and 5 colonies across the North-Atlantic from Shetland to Svalbard. The ΣHOCs levels in plasma ranged across two orders of magnitude, from 40 to 7600 ng/g (wet weight) and differed significantly across the great Skua colonies. The variation in contaminant occurrence among colonies did not reflect long-range transport through a latitudinal or remoteness gradient, as the second northernmost colony (Bjornoya), had the highest contaminant concentrations. No latitudinal or remoteness gradient was evident in the contaminant pattern among the colonies. The contaminant levels increased significantly with increasing δ15N values, and regurgitated pellets of undigested prey suggested that great Skuas with higher δ15N values had a higher proportion of bird prey in their diet, mostly seabirds. In contrast, great Skuas from colonies with lower δ15N and lower contaminant level fed mostly on fish. The enrichment of δ13C increased with decreasing δ15N and lower contaminant levels. Therefore, individual behavior of great Skuas, such as migration strategies and diet specialization, rather than long-range transport and thus baseline food web exposure, explain among and within colony variance in contaminant occurrence.
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Plastic debris in great Skua (Stercorarius Skua) pellets corresponds to seabird prey species
Marine Pollution Bulletin, 2016Co-Authors: Sarah Hammer, P. C.d. Johnson, Robert W Furness, Ruedi G. Nager, Jennifer F. ProvencherAbstract:Plastic is a common item in marine environments. Studies assessing seabird ingestion of plastics have focused on species that ingest plastics mistaken for prey items. Few studies have examined a scavenger and predatory species that are likely to ingest plastics indirectly through their prey items, such as the great Skua (Stercorarius Skua). We examined 1034 regurgitated pellets from a great Skua colony in the Faroe Islands for plastics and found approximately 6% contained plastics. Pellets containing remains of Northern fulmars (Fulmarus glacialis) had the highest prevalence of plastic. Our findings support previous work showing that Northern fulmars have higher loads of plastics than other sympatric species. This study demonstrates that marine plastic debris is transferred from surface feeding seabird species to predatory great Skuas. Examination of plastic ingestion in species that do not ingest plastics directly can provide insights into how plastic particles transfer vertically within the food web.
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density dependence in seabirds great Skuas stercorarius Skua start to breed at a younger age when conditions are better
Ringing and Migration, 2015Co-Authors: Robert W FurnessAbstract:Large-scale and long-term ringing and cohort colour ringing of chicks, combined with trapping of immatures on clubs and adults on nests, allows the age of first breeding by Great Skuas Stercorarius Skua to be investigated. Modal and median age of first breeding of Great Skuas at their largest colony (Foula, Shetland) was seven years, but there was considerable individual variation. Birds may first breed when four to >11 years old. Compared with the situation in Foula, Great Skuas start breeding at a younger age at smaller colonies. When conditions at Foula deteriorated, resulting in reduced adult survival, reduced breeding success and population decline, age of first breeding increased. These patterns imply a density-dependent age of first breeding, but with individual variation because higher-quality birds recruit at a younger age than birds in poor body condition. Density-dependent variation in age at first breeding may have an important influence on population growth rate, and this would merit study al...
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great Skua stercorarius Skua movements at sea in relation to marine renewable energy developments
Marine Environmental Research, 2014Co-Authors: Helen M Wade, Elizabeth A Masden, Angus C Jackson, Chris B Thaxter, Niall H K Burton, W. Bouten, Robert W FurnessAbstract:Marine renewable energy developments (MREDs) are an increasing feature of the marine environment. Owing to the relatively small number of existing developments and the early stage of their associated environmental monitoring programmes, the effects of MREDs on seabirds are not fully known. Our ability to fully predict potential effects is limited by a lack of knowledge regarding movements of seabirds at sea. We used GPS tracking to improve our understanding of the movements at sea of a protected seabird species breeding in Scotland, the great Skua (Stercorarius Skua), to better predict how this species may be affected by MREDs. We found that the overlap of great Skuas with leased and proposed MREDs was low; particularly with offshore wind sites, which are predicted to present a greater risk to great Skuas than wave or tidal-stream developments. Failed breeders overlapped with larger areas of MREDs than breeding birds but the overall overlap with core areas used remained low. Overlap with wave energy development sites was greater than for offshore wind and tidal-stream sites. Comparison of 2011 data with historical data indicates that distances travelled by great Skuas have likely increased over recent decades. This suggests that basing marine spatial planning decisions on short-term tracking data could be less informative than longer-term data.
Stephen C Votier - One of the best experts on this subject based on the ideXlab platform.
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Conservation implications of variation in diet and dietary specialisation in great Skuas
2020Co-Authors: Stephen C VotierAbstract:1. Great Skuas Catharacta Skua are the only member of the genus Catharacta in the northern hemisphere. The UK holds around 60% of the World population with 8,000 breeding pairs. 2. Sustained population growth of the great Skua in Scotland during the last century appears attributable to an abundant supply of discards (from commercial fisheries) and sandeels Ammodytes marinus. In addition great Skuas may scavenge or predate other seabirds and their chicks when other prey is in short supply. 3. Following a decline in sandeels in the 1980s there is some evidence that an increase in predation of seabirds by great Skuas may be affecting seabird populations. Future measures to reduce the amounts of fish discarded may result in a further increase in predation by great Skuas. This highlights the need to quantify the current impact of great Skua predation on seabird populations, and monitor any future change. 4. Accurate assessment of great Skua diet is fundamental to this type of research. Many studies have used pellets of indigestible prey to assess diet in Skuas and gulls, but have not quantified this technique. Captive great Skuas were fed a range of fish and birds to try and understand more fully how pellets reflect diet. Feeding trials showed that Skuas fed on a diet of birds produced more pellets than when feeding on fish. Fish species strongly influenced the number of pellets produced as well as the proportion and size of otoliths recovered. The numbers of pellets cast also varied significantly among differing species of bird meals. Field trials revealed that only a small proportion of pellets produced are being sampled. This study highlights the need to carefully validate the use of pellets to assess diet, particularly in a species of conservation concern. 5. The diet of great Skuas was estimated based on five different techniques (pellets, prey remains, spontaneous regurgitates, observed feeds and water off-loading) and the results compared. The diet composition based on five sampling techniques in a single year generally showed a good correlation with one another. However comparing the proportion of the three main prey types estimated by four sampling techniques over three years revealed a significant interactive effect of year and sampling technique on the diet composition. While estimates of diet using different sampling techniques may be broadly comparable, technique dependent biases mean that the advantages and disadvantages of each sampling technique need to be borne in mind before conducting diet studies. A small proportion of great Skuas breeding at Hermaness, Shetland exhibit distinct dietary specialisation, feeding almost exclusively upon seabird prey. Around half of these "bird-specialists" defend feeding territories within a section of seabird colony, the remainder foraging away from breeding territories. "Bird-specialists" retained their feeding habit and, if present, territory, between years. Time-budgets revealed that "bird-specialists" with feeding territories spent less time foraging than "bird-specialists" without a feeding territory or Skuas feeding predominantly on fish. Results of radiotracking great Skuas for the first time suggest that "bird-specialists" have smaller home ranges than "others". In all years "bird-specialists" show similar productivity to "others", but earlier hatching dates (a good measure of quality in great Skuas). While we do not know whether high quality Skuas feed on seabirds or that feeding on seabirds advances laying date, hatching early is likely to confer an advantage to "bird- specialists". Non-specialist great Skuas experienced a reduction in clutch volume and chick condition during 1999, compared with 1998 - presumably due to a reduction in food availability. "Bird-specialists" did not experience a similar decline in clutch volume and chick condition between years, and showed higher clutch volume and chick condition than "others" in 1999. In addition to changes in clutch volume and chick condition, adult non-specialists showed reduced annual survival, compared with "bird-specialists" over the same period. These results suggest that "bird-specialists" not only have earlier hatching dates in all years, but in certain years also gain an advantage in terms of improved chick condition and adult survival that may have implications for lifetime reproductive success (LRS). Apparent fitness benefits derived from specialising in bird predation may have conservation implications for seabirds colonies in Shetland.
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change in the north sea ecosystem from the 1970s to the 2010s great Skua diets reflect changing forage fish seabirds and fisheries
Ices Journal of Marine Science, 2019Co-Authors: Gabriella E Church, Robert W Furness, Glen Tyler, Lucy Gilbert, Stephen C VotierAbstract:Understanding anthropogenic impacts are crucial to maintain marine ecosystem health. The North Sea has changed in recent decades, largely due to commercial fishing and climate change. Seabirds can act as useful indicators of these changes. By analyzing n = 20 013 pellets and n = 24 993 otoliths regurgitated by great Skuas Stercorarius Skua in northern Scotland over five decades from the 1970s to the 2010s (in 36 years 1973–2017), we reveal how the diet of this top predator has changed alongside the changing North Sea ecosystem. Sandeels Ammodytes spp. were the most common dietary item during the 1970s, but became virtually absent from the 1980s onward. Discarded whitefish dominated Skua diets from the 1980s to the present day, despite long-term declines in North Sea discard production. However, the discarded fish eaten by great Skuas has become smaller and the species composition changed. Skua pellets only rarely contained avian prey in the 1970s but this increased during the 1980s, and fluctuated between 10% and 20% from the 1990s to 2010s. There have also been changes in the avian prey in the diet—black-legged kittiwakes Rissa tridactyla generally being replaced by auks Alcid spp. and northern fulmars Fulmarus glacialis. The Shetland marine ecosystem has experienced steep declines in sandeel stocks and in seabirds that feed on them. Great Skuas have been able to prey switch to respond to this change, supported by abundant discards, enabling them to maintain a favourable population status while other seabird species have declined.
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using inter colony variation in demographic parameters to assess the impact of Skua predation on seabird populations
Ibis, 2008Co-Authors: Stephen C Votier, Martin Heubeck, Robert W FurnessAbstract:Large Skuas and gulls are top predators in marine ecosystems, feeding on shoaling fish, fishery discards and facultatively on smaller seabirds. As generalist predators they may have deleterious impacts on prey populations of seabirds, particularly when alternative foods are scarce. Declines in discards and lipid-rich shoaling fish may result in these large scavenging birds turning to prey on seabirds to meet their nutritional needs, yet we know relatively little about seabird predator–prey dynamics. Declines in Black-legged Kittiwakes Rissa tridactyla in the UK are attributed to reductions in Sandeel Ammodytes marinus availability, but may also be due to predation by Great Skuas Stercorarius Skua in some parts of their range. We investigate whether variation in two demographic parameters (breeding success and population growth rate) of Kittiwake colonies across Shetland are explained by Skua population density at increasing spatial scales (rings with radii of 0–5, 5–10, 10–15, 15–20, 20–25 and 25–30 km) and Kittiwake population density. These explanatory variables do not explain a significant amount of the variation in annual population growth rate (lambda), but our estimate of population change is highly conservative and we cannot exclude the possibility of type II errors. Kittiwake breeding success is positively correlated with Sandeel availability and negatively correlated with the number of Kittiwakes at the focal colony. Having controlled for these effects the number of Great Skuas also has an influence on breeding success, being negatively correlated at the scale of 5–10 and 20–25 km, but positively correlated at the scale of 10–15 km. In addition, analysis of Kittiwake populations subdivided into exposed or protected cliffs reveals that exposed sub-colonies declined more steeply than protected ones – presumably as a function of differences in susceptibility to Skua predation. We propose that comparing differences in demographic rates may be useful in unravelling seabird predator–prey dynamics, but only where there is a comprehensive demographic dataset, where it is possible to correct for confounding factors such as food availability, and information on habitat–predation interactions.
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seabird predation by great Skuas stercorarius Skua intra specific competition for food
Journal of Avian Biology, 2007Co-Authors: Stephen C Votier, Jonathan E. Crane, Stuart Bearhop, Jose Manuel Arcos, Robert W FurnessAbstract:Competition for food is widely cited as an important cost of coloniality among birds and much of the evidence in support of this hypothesis comes from studies of colonial piscivorous seabirds. However, for generalist seabirds able to switch between different prey types, the role of food availability in relation to colony size is unclear. Here we investigate patterns of the consumption of seabird prey in relation to colony size in a generalist seabird, the great Skua Stercorarius Skua, in Shetland, UK. At the population level Skuas feed mainly on sandeels Ammodytes marinus and fishery discards, but respond to declines in fish availability to facultatively prey on other seabirds. By comparing the consumption of seabirds among seven different sized colonies, including one colony with artificially reduced numbers of Skuas (Fair Isle), we investigate whether consumption of seabird prey is influenced by Skua population size, while simultaneously measuring seabird prey availability. Data from five years also enables us to investigate the influence of annual variation in environmental conditions on seabird consumption. Using measures of body condition and reproductive performance we investigate the consequences of living in different sized colonies, which may provide insight into ultimate costs of nesting at high population density. Skua diets varied among colonies and the proportion of seabird prey in the diet was inversely related to Skua colony size, despite similar per capita numbers of seabirds across colonies. At the colony where their numbers were artificially suppressed, Skuas consumed a greater proportion of seabirds per capita. Highly significant year effects in seabird predation were observed but the pattern among colonies remained consistent over time. Two measures of adult body condition (pectoral muscle index and mean corpuscular volume) revealed that adult great Skuas were in poorer condition at the largest colony (Foula), but reproductive performance did not alter significantly among colonies. This study provides evidence that intra-specific competition among Skuas may limit opportunities for obtaining seabird prey, which may be particularly important during periods of poor availability of sandeels and fishery discards, and has implications for assessing the impact of Skuas on seabird populations.
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Seabird predation by great Skuas Stercorarius Skua– intra‐specific competition for food?
Journal of Avian Biology, 2007Co-Authors: Stephen C Votier, Jonathan E. Crane, Stuart Bearhop, Jose Manuel Arcos, Robert W FurnessAbstract:Competition for food is widely cited as an important cost of coloniality among birds and much of the evidence in support of this hypothesis comes from studies of colonial piscivorous seabirds. However, for generalist seabirds able to switch between different prey types, the role of food availability in relation to colony size is unclear. Here we investigate patterns of the consumption of seabird prey in relation to colony size in a generalist seabird, the great Skua Stercorarius Skua, in Shetland, UK. At the population level Skuas feed mainly on sandeels Ammodytes marinus and fishery discards, but respond to declines in fish availability to facultatively prey on other seabirds. By comparing the consumption of seabirds among seven different sized colonies, including one colony with artificially reduced numbers of Skuas (Fair Isle), we investigate whether consumption of seabird prey is influenced by Skua population size, while simultaneously measuring seabird prey availability. Data from five years also enables us to investigate the influence of annual variation in environmental conditions on seabird consumption. Using measures of body condition and reproductive performance we investigate the consequences of living in different sized colonies, which may provide insight into ultimate costs of nesting at high population density. Skua diets varied among colonies and the proportion of seabird prey in the diet was inversely related to Skua colony size, despite similar per capita numbers of seabirds across colonies. At the colony where their numbers were artificially suppressed, Skuas consumed a greater proportion of seabirds per capita. Highly significant year effects in seabird predation were observed but the pattern among colonies remained consistent over time. Two measures of adult body condition (pectoral muscle index and mean corpuscular volume) revealed that adult great Skuas were in poorer condition at the largest colony (Foula), but reproductive performance did not alter significantly among colonies. This study provides evidence that intra-specific competition among Skuas may limit opportunities for obtaining seabird prey, which may be particularly important during periods of poor availability of sandeels and fishery discards, and has implications for assessing the impact of Skuas on seabird populations.
Eliza H K Leat - One of the best experts on this subject based on the ideXlab platform.
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Persistent organic pollutants in great Skuas Stercorarius Skua
2020Co-Authors: Eliza H K LeatAbstract:The bioaccumulation of persistent organic pollutants (POPs) is of particular environmental concern in top predators, which accumulate high concentrations of POPs that can cause adverse effects. Previous small scale studies found high concentrations of POPs in adult great Skuas, Stercorarius Skua, a top predator in the marine environment. This thesis investigates the factors affecting concentrations and patterns of POPs (contribution of individual POPs to the ΣPOPs) in the great Skua across its breeding range in the north-east Atlantic. Clear differences between colonies in both concentration and pattern of POPs in adult plasma were not indicative of being caused by long range transport of POPs in the atmosphere. Variation in diet between colonies is the mostly likely explanation for these colony differences, with great Skuas from some colonies having a greater proportion of fish in their diet whilst others eat more seabird prey. Although seabirds are often used in studies of POPs in the environment, the effect of migratory behaviour has not previously been studied in detail. By using a combination of global location sensor (GLS) loggers and feather stable isotopes from winter grown feathers, the wintering areas of individuals from three breeding populations of great Skuas were identified. Great Skuas spend the winter in three distinct areas across the North Atlantic, with birds from the same breeding colonies wintering in different areas. In two of the three breeding populations, wintering area explained a significant proportion of variation in organochlorines (OCs) concentrations and pattern. However in the colony with the highest concentrations of OCs, no effect of wintering area was found, possibly as a result of these great Skuas feeding at a higher trophic level during the breeding season than other populations. Temporally, concentrations of OCs were higher in 1980 than 2008 in eggs, whilst newer contaminants polybrominated diphenyl ethers (PBDEs) and perfluorinated chemicals (PFASs) show the opposite trend. In conclusion, concentrations of POPs in the great Skua were influenced primarily by breeding season diet with wintering area and sex also having small but significant effects on POPs. Wintering area explained the most variation in the pattern of POPs in great Skuas. The POP concentrations found in this study exceeded those which have been found to cause adverse effects on the immune system and reproduction in other species of seabird.
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the effect of long range transport trophic position and diet specialization on legacy contaminant occurrence in great Skuas stercorarius Skua breeding across the northeast atlantic
Environmental Pollution, 2019Co-Authors: Eliza H K Leat, Robert W Furness, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Tor Harry Bjorn, Geir W Gabrielsen, Jan Ove Bustnes, Ane HaarrAbstract:Abstract High levels of halogenated organic contaminants (HOCs) have been found in the marine predatory seabird great Skua (Stercorarius Skua) from breeding colonies in the Northeastern Atlantic, with large unexplained inter-colony variation. The present study aimed at analyzing if the HOCs occurrence in breeding great Skuas in remote colonies was explained by local baseline food web exposure determined by long-range transport, or by ecological factors such as diet specialization and relative trophic position in the breeding area. The occurrence of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) was analyzed in plasma of 204 adult great Skuas collected over two years (2008 and 2009) and 5 colonies across the North-Atlantic from Shetland to Svalbard. The ΣHOCs levels in plasma ranged across two orders of magnitude, from 40 to 7600 ng/g (wet weight) and differed significantly across the great Skua colonies. The variation in contaminant occurrence among colonies did not reflect long-range transport through a latitudinal or remoteness gradient, as the second northernmost colony (Bjornoya), had the highest contaminant concentrations. No latitudinal or remoteness gradient was evident in the contaminant pattern among the colonies. The contaminant levels increased significantly with increasing δ15N values, and regurgitated pellets of undigested prey suggested that great Skuas with higher δ15N values had a higher proportion of bird prey in their diet, mostly seabirds. In contrast, great Skuas from colonies with lower δ15N and lower contaminant level fed mostly on fish. The enrichment of δ13C increased with decreasing δ15N and lower contaminant levels. Therefore, individual behavior of great Skuas, such as migration strategies and diet specialization, rather than long-range transport and thus baseline food web exposure, explain among and within colony variance in contaminant occurrence.
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contrasting effects of gps device and harness attachment on adult survival of lesser black backed gulls larus fuscus and great Skuas stercorarius Skua
Ibis, 2016Co-Authors: Chris B Thaxter, Elizabeth A Masden, Helen M Wade, Eliza H K Leat, Viola H Rosssmith, Jacquie A Clark, Nigel A Clark, Greg J Conway, Sheila C Gear, Mike MarshAbstract:Telemetry has become an important method for studying the biology and ecology of animals. However, the impact of tracking devices and their method of attachment on different species across multiple temporal scales has seldom been assessed. We compared the behavioural and demographic responses of two species of seabird, Lesser Black-backed Gull Larus fuscus and Great Skua Stercorarius Skua, to a GPS device attached using a crossover wing harness. We used telemetry information and monitoring of breeding colonies to compare birds equipped with a device and harness, and control birds without an attachment. We assessed whether tagged birds have lower short-term breeding productivity or lower longer term overwinter return rates (indicative of overwinter survival) than controls. For Great Skua, we also assessed whether territory attendance within the breeding season differed between tagged and control birds. As with previous studies on Lesser Black-backed Gull, we found no short-term impacts on breeding productivity or long-term impacts on overwinter return rates. For Great Skua, there was no evidence for impacts of the device and harness on territory attendance or breeding productivity. However, as found by a previous study of Great Skuas using a different (body) harness design, there was strong evidence of reduced overwinter return rates. Consequently, a device attached using a wing harness was considered suitable for long-term deployment on Lesser Black-backed Gulls, but not on Great Skuas. These findings will inform the planning of future tracking studies.
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Contrasting effects of GPS device and harness attachment on adult survival of Lesser Black‐backed Gulls Larus fuscus and Great Skuas Stercorarius Skua
Ibis, 2016Co-Authors: Chris B Thaxter, Elizabeth A Masden, Helen M Wade, Eliza H K Leat, Jacquie A Clark, Nigel A Clark, Greg J Conway, Sheila C Gear, Viola H. Ross-smith, Mike MarshAbstract:Telemetry has become an important method for studying the biology and ecology of animals. However, the impact of tracking devices and their method of attachment on different species across multiple temporal scales has seldom been assessed. We compared the behavioural and demographic responses of two species of seabird, Lesser Black-backed Gull Larus fuscus and Great Skua Stercorarius Skua, to a GPS device attached using a crossover wing harness. We used telemetry information and monitoring of breeding colonies to compare birds equipped with a device and harness, and control birds without an attachment. We assessed whether tagged birds have lower short-term breeding productivity or lower longer term overwinter return rates (indicative of overwinter survival) than controls. For Great Skua, we also assessed whether territory attendance within the breeding season differed between tagged and control birds. As with previous studies on Lesser Black-backed Gull, we found no short-term impacts on breeding productivity or long-term impacts on overwinter return rates. For Great Skua, there was no evidence for impacts of the device and harness on territory attendance or breeding productivity. However, as found by a previous study of Great Skuas using a different (body) harness design, there was strong evidence of reduced overwinter return rates. Consequently, a device attached using a wing harness was considered suitable for long-term deployment on Lesser Black-backed Gulls, but not on Great Skuas. These findings will inform the planning of future tracking studies.
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activity patterns of wintering great Skuas stercorarius Skua
Bird Study, 2014Co-Authors: Ellen Magnusdottir, Richard A Phillips, Eliza H K Leat, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Jan Ove Bustnes, Jon Einar Jonsson, Robert W FurnessAbstract:Capsule Great Skuas Stercorarius Skua wintering in different areas spent different amounts of time in flight (foraging or searching for food) and so may be experiencing different feeding conditions.Aims To compare the daily percentage of time spent in flight (foraging or searching for food) between different wintering areas.Methods In 2008, loggers equipped with a saltwater sensor were deployed on adult Great Skuas at three colonies in the northeast Atlantic, and the data used to compare foraging activity between the five main wintering areas.Results The five areas used by 22 Great Skuas in winter were widely separated, from the northwest Atlantic to northwest Africa, and differ substantially in oceanography. The main difference in foraging effort among areas for individuals that were site-faithful was that the percentage of time per day spent in flight off northwest Africa was much lower than elsewhere. Among five birds that travelled between wintering areas, one reduced the percentage of time in flight ...
Sophie Bourgeon - One of the best experts on this subject based on the ideXlab platform.
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the effect of long range transport trophic position and diet specialization on legacy contaminant occurrence in great Skuas stercorarius Skua breeding across the northeast atlantic
Environmental Pollution, 2019Co-Authors: Eliza H K Leat, Robert W Furness, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Tor Harry Bjorn, Geir W Gabrielsen, Jan Ove Bustnes, Ane HaarrAbstract:Abstract High levels of halogenated organic contaminants (HOCs) have been found in the marine predatory seabird great Skua (Stercorarius Skua) from breeding colonies in the Northeastern Atlantic, with large unexplained inter-colony variation. The present study aimed at analyzing if the HOCs occurrence in breeding great Skuas in remote colonies was explained by local baseline food web exposure determined by long-range transport, or by ecological factors such as diet specialization and relative trophic position in the breeding area. The occurrence of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) was analyzed in plasma of 204 adult great Skuas collected over two years (2008 and 2009) and 5 colonies across the North-Atlantic from Shetland to Svalbard. The ΣHOCs levels in plasma ranged across two orders of magnitude, from 40 to 7600 ng/g (wet weight) and differed significantly across the great Skua colonies. The variation in contaminant occurrence among colonies did not reflect long-range transport through a latitudinal or remoteness gradient, as the second northernmost colony (Bjornoya), had the highest contaminant concentrations. No latitudinal or remoteness gradient was evident in the contaminant pattern among the colonies. The contaminant levels increased significantly with increasing δ15N values, and regurgitated pellets of undigested prey suggested that great Skuas with higher δ15N values had a higher proportion of bird prey in their diet, mostly seabirds. In contrast, great Skuas from colonies with lower δ15N and lower contaminant level fed mostly on fish. The enrichment of δ13C increased with decreasing δ15N and lower contaminant levels. Therefore, individual behavior of great Skuas, such as migration strategies and diet specialization, rather than long-range transport and thus baseline food web exposure, explain among and within colony variance in contaminant occurrence.
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activity patterns of wintering great Skuas stercorarius Skua
Bird Study, 2014Co-Authors: Ellen Magnusdottir, Richard A Phillips, Eliza H K Leat, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Jan Ove Bustnes, Jon Einar Jonsson, Robert W FurnessAbstract:Capsule Great Skuas Stercorarius Skua wintering in different areas spent different amounts of time in flight (foraging or searching for food) and so may be experiencing different feeding conditions.Aims To compare the daily percentage of time spent in flight (foraging or searching for food) between different wintering areas.Methods In 2008, loggers equipped with a saltwater sensor were deployed on adult Great Skuas at three colonies in the northeast Atlantic, and the data used to compare foraging activity between the five main wintering areas.Results The five areas used by 22 Great Skuas in winter were widely separated, from the northwest Atlantic to northwest Africa, and differ substantially in oceanography. The main difference in foraging effort among areas for individuals that were site-faithful was that the percentage of time per day spent in flight off northwest Africa was much lower than elsewhere. Among five birds that travelled between wintering areas, one reduced the percentage of time in flight ...
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feather corticosterone levels on wintering grounds have no carry over effects on breeding among three populations of great Skuas stercorarius Skua
PLOS ONE, 2014Co-Authors: Sophie Bourgeon, Robert W Furness, Eliza H K Leat, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Geir W Gabrielsen, Ellen Magnusdottir, Jan Ove BustnesAbstract:Environmental conditions encountered by migratory seabirds in their wintering areas can shape their fitness. However, the underlying physiological mechanisms remain largely unknown as birds are relatively inaccessible during winter. To assess physiological condition during this period, we measured corticosterone concentrations in winter-grown primary feathers of female great Skuas (Stercorarius Skua) from three breeding colonies (Bjornoya, Iceland, Shetland) with wintering areas identified from characteristic stable isotope signatures. We subsequently compared winter feather corticosterone levels between three wintering areas (Africa, Europe and America). Among females breeding in 2009, we found significant differences in feather corticosterone levels between wintering areas. Surprisingly, levels were significantly higher in Africa despite seemingly better local ecological factors (based on lower foraging effort). Moreover, contrary to our predictions, females sharing the same wintering grounds showed significant differences in feather corticosterone levels depending on their colony of origin suggesting that some Skuas could be using suboptimal wintering areas. Among females wintering in Africa, Shetland females showed feather corticosterone levels on average 22% lower than Bjornoya and Iceland females. Finally, the lack of significant relationships between winter feather corticosterone levels and any of the breeding phenology traits does not support the hypothesis of potential carry-over effects of winter feather corticosterone. Yet, the fitness consequences of elevated feather corticosterone levels remain to be determined.
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organohalogen contaminants and blood plasma clinical chemical parameters in three colonies of north atlantic great Skua stercorarius Skua
Ecotoxicology and Environmental Safety, 2013Co-Authors: Christian Sonne, Eliza H K Leat, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Geir W Gabrielsen, Frank F Riget, Katrine Borga, Kristin OlafsdottirAbstract:The present study compares blood plasma clinical–chemical parameters (BCCPs) in birds from three geographically distinct North Atlantic Great Skua (Stercorarius Skua) colonies. Birds from these sites bioaccumulate different POP (persistent organic pollutant) concentrations and that enabled us to compare Great Skua BCCPs in different exposure scenarios. Persistent organic pollutants (organochlorines: PCB, DDT, chlordanes, HCB, HCH, mirex and brominated flame retardants: PBDEs) and nineteen BCCPs were analysed in 114 adult Great Skuas sampled during summer 2009 in North Atlantic colonies at Bjornoya (n=42), Iceland (n=57) and Shetland (n=15). Specimens from Bjornoya had the highest blood plasma concentrations of all contaminant groups followed by Iceland and Shetland birds, respectively (ANOVA: p 0.05). Therefore correlation analyses of these seven BCCPs vs. POPs were done on the combined colony data while the analyses of the remaining 12 BCCPs were carried out for each colony separately. The analyses of combined colony data showed that the blood plasma concentration of liver enzymes ALAT and GGT increased with increasing concentrations of ΣPBDE and ΣHCH, HCB and ΣCHL, respectively (all Pearson's p<0.05). In Great Skuas from Shetland, the important osmotic transport protein albumin increased with increasing concentrations of ΣPCB and ΣDDT, while total blood plasma protein increased with ΣPCB, ΣDDT, ΣHCH and HCB concentrations (all Pearson's p<0.05). In both Bjornoya and Iceland Skuas, blood plasma pancreatic enzyme amylase decreased with increasing ΣHCH concentrations while the erythrocyte waste product total bilirubin in blood plasma increased with increasing ΣHCH and ΣPBDE concentrations in Iceland Great Skuas (all Pearson's p<0.05). In Bjornoya birds, blood plasma urea from protein metabolism (reflects kidney function) increased with increasing ΣPBDE concentrations (Pearson's p<0.05). Furthermore, a redundancy analysis showed that 10.6% of the variations in BCCPs could be explained by the variations in POP concentrations. Based on these results we suggest that liver and renal functions could be negatively affected by different POP compounds. It is, however, uncertain if the colony BCCP differences and their relationship to POP concentrations reflect health effects that could have an overall impact on the populations via reduced survival and reproduction parameters.
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Organohalogen contaminants and Blood plasma clinical-chemical parameters in three colonies of North Atlantic Great Skua (Stercorarius Skua).
Ecotoxicology and Environmental Safety, 2013Co-Authors: Christian Sonne, Eliza H K Leat, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Geir W Gabrielsen, Frank F Riget, Katrine Borga, Kristin OlafsdottirAbstract:The present study compares blood plasma clinical–chemical parameters (BCCPs) in birds from three geographically distinct North Atlantic Great Skua (Stercorarius Skua) colonies. Birds from these sites bioaccumulate different POP (persistent organic pollutant) concentrations and that enabled us to compare Great Skua BCCPs in different exposure scenarios. Persistent organic pollutants (organochlorines: PCB, DDT, chlordanes, HCB, HCH, mirex and brominated flame retardants: PBDEs) and nineteen BCCPs were analysed in 114 adult Great Skuas sampled during summer 2009 in North Atlantic colonies at Bjornoya (n=42), Iceland (n=57) and Shetland (n=15). Specimens from Bjornoya had the highest blood plasma concentrations of all contaminant groups followed by Iceland and Shetland birds, respectively (ANOVA: p 0.05). Therefore correlation analyses of these seven BCCPs vs. POPs were done on the combined colony data while the analyses of the remaining 12 BCCPs were carried out for each colony separately. The analyses of combined colony data showed that the blood plasma concentration of liver enzymes ALAT and GGT increased with increasing concentrations of ΣPBDE and ΣHCH, HCB and ΣCHL, respectively (all Pearson's p
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activity patterns of wintering great Skuas stercorarius Skua
Bird Study, 2014Co-Authors: Ellen Magnusdottir, Richard A Phillips, Eliza H K Leat, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Jan Ove Bustnes, Jon Einar Jonsson, Robert W FurnessAbstract:Capsule Great Skuas Stercorarius Skua wintering in different areas spent different amounts of time in flight (foraging or searching for food) and so may be experiencing different feeding conditions.Aims To compare the daily percentage of time spent in flight (foraging or searching for food) between different wintering areas.Methods In 2008, loggers equipped with a saltwater sensor were deployed on adult Great Skuas at three colonies in the northeast Atlantic, and the data used to compare foraging activity between the five main wintering areas.Results The five areas used by 22 Great Skuas in winter were widely separated, from the northwest Atlantic to northwest Africa, and differ substantially in oceanography. The main difference in foraging effort among areas for individuals that were site-faithful was that the percentage of time per day spent in flight off northwest Africa was much lower than elsewhere. Among five birds that travelled between wintering areas, one reduced the percentage of time in flight ...
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wintering areas of great Skuas stercorarius Skua breeding in scotland iceland and norway
Bird Study, 2012Co-Authors: Ellen Magnusdottir, Richard A Phillips, Eliza H K Leat, Sophie Bourgeon, Sveinn Are Hanssen, Aevar Petersen, Hallvard Strom, Jan Ove Bustnes, Pall Hersteinsson, Robert W FurnessAbstract:Capsule Great Skuas Stercorarius Skua breeding in Scotland, Iceland, and Norway, winter in different areas. Aims To assess the winter distribution of adult Great Skuas breeding in different countries. Methods Geolocation data-loggers were deployed on breeding adults at colonies in Shetland (Scotland), southeast Iceland, and Bjornoya (Norway) in 2008. Loggers were recovered when birds returned to breed the next year and downloaded data were processed to indicate the location of each individual throughout the winter period. Results Adult Great Skuas from Scotland wintered off northwest Africa and southern Europe. Adults from Iceland mostly wintered off Canada, with small numbers visiting northwest Africa and Europe. Although adults from Bjornoya (Norway) migrated to similar areas to birds from Iceland, a slightly greater proportion wintered off Europe, and most used areas further north than birds from Scotland. Although three birds studied over consecutive winters used the same small area in consecutive years, four moved between different areas within one winter. Conclusion Great Skuas show clear variation in migrations among breeding regions, and some evidence of individual consistency.
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phylogeography of the southern Skua complex rapid colonization of the southern hemisphere during a glacial period and reticulate evolution
Molecular Phylogenetics and Evolution, 2008Co-Authors: Markus S. Ritz, Richard A Phillips, Gary D. Miller, Peter G Ryan, Craig D Millar, Viviane Sternkopf, Dorit Liebershelbig, Hans-ulrich PeterAbstract:Whilst we have now a good understanding how past glaciation influenced species at the northern hemisphere, our knowledge of patterns and modes of speciation is far more limited for the southern hemisphere. We provide mtDNA based data on the phylogeography of a circumpolar distributed southern hemisphere seabird group—the southern Skua complex (Catharacta spp.). Diversification of southern Skuas dates between 210,000 yBP and 150,000 yBP and coincides with a glacial spanning 230,000–140,000 yBP. Skuas most likely first inhabited the Antarctic continent, in the course of global cooling and increasing glaciation spread to the sub-antarctic islands and Tristan da Cunha and finally colonized Patagonia and the Falkland Islands at the glacial maximum. Despite significant differences between taxa most populations still exchange genes with neighboring populations of other taxa and speciation is incomplete.
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Nocturnal foraging by great Skuas Stercorarius Skua: implications for conservation of storm-petrel populations
Journal of Ornithology, 2006Co-Authors: Stephen C Votier, Jonathan E. Crane, Ana León, Claire A. Mcsorley, Eduardo Mínguez, Ian P. Mitchell, Stuart Bearhop, Richard A Phillips, Matthew Parsons, Robert W FurnessAbstract:At St Kilda, Outer Hebrides, a large colony of great Skuas Stercorarius Skua feed extensively on one of the largest colonies of Leach’s storm-petrels Oceanodroma leucorhoa in Europe, but little is known about the dynamics of this predator–prey system. Recently published population estimates of storm-petrels make it possible to estimate the impact of Skua predation for the first time. Although Skuas in the southern hemisphere catch petrels attending breeding colonies at night, it is not known whether congeners in the northern hemisphere also forage during the hours of darkness. We found (using radio-transmitters) that Skuas regularly forage at night and (using light intensifying equipment) observed them catching storm-petrels at night. However, Skuas also foraged during daylight hours, and it is unknown whether they might also catch storm-petrels at sea. Data on diet composition reveals that the proportion of storm-petrels in Skua diet declined between 1996 and 1997, but remained constant thereafter. Although a large proportion of the storm-petrel prey is likely to consist of non-breeders, numbers consumed suggest that breeders and an unknown quantity of transients may also been eaten. The numbers of storm-petrels eaten are not sustainable and may result in substantial long-term population declines. Under current conditions, maintenance of large populations of both Leach’s storm-petrels and great Skuas at St Kilda appears to be mutually exclusive.
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Predation by great Skuas at a large Shetland seabird colony
Journal of Applied Ecology, 2004Co-Authors: Stephen C Votier, Stuart Bearhop, Richard A Phillips, Norman Ratcliffe, Robert W FurnessAbstract:Summary 1. Skuas are top predators in marine ecosystems and may have detrimental effects on seabird communities they prey upon. However, predation rates are poorly understood and poorly quantified. Using a bio-energetics model we estimate seabird predation by great Skuas, Stercorarius Skua , at a large UK colony (Hermaness, Shetland). We investigate the influence of dietary specialization and fishery management on predation and explore the effect of experimental removal of specialist bird predators. 2. Great Skuas at Hermaness required 491·5 × 10 6 kJ and 546·6 × 10 6 kJ of energy in each of two breeding seasons. Breeding Skuas fell into one of two groups: a small proportion (5%) of specialist bird predators or the vast majority (95%) that fed opportunistically on birds or specialized on fishery discards. During 1999, great Skuas consumed ≈ 80 000 kg of fish, which increased to over 90 000 kg in 2001. About 13 000 seabirds were consumed by great Skuas each year, with 26‐29% being consumed by specialist bird predators. 3. Although it is difficult to assess, great Skuas appear to be having a negative impact on seabird populations. Altering model inputs to test differing scenarios revealed that reductions in fishery discards would result in increased seabird predation rates. However, proposed changes in fishery management over the period of the study did not reduce discarding rates, which instead increased. 4. Synthesis and applications . The use of a bioenergetics model reveals that great Skua predation may negatively affect seabird populations. Availability of fishery discards is an important factor influencing seabird predation rates, but predicting the effect of changes in fishery management may be difficult in the short term. Specialist bird predators consume large quantities of seabird prey, but this is less significant at the population level. Although experimental removal of specialist bird predators may reduce predation at a minimal loss of Skuas, it is unclear whether conspecifics may replace them and retain high rates of predation.