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Capsule Morphometrics, plumage and mitochondrial DNA of Common Eiders Somateria mollissima in Shetland indicate that these birds should be classified as subspecies faeroeensis. Aims To test whether molecular data support the suggestion based on measurements that Common Eiders in Shetland belong to the subspecies faeroeensis. Methods DNA extracted from Common Eiders found dead in Shetland was amplified and a section of the mitochondrial genome was sequenced to compare with data from birds previously sampled from Iceland, Faroes, east England and continental Europe. Results Shetland Common Eiders are closely similar to birds from the Faroe Islands classified as subspecies faeroeensis, and somewhat distinct from the nominate mollissima to which all Scottish eiders have been conventionally assigned. Eiders from southern Iceland have haplotypes more similar to faeroeensis despite differing in plumage and being assigned on plumage to a different subspecies borealis. Conclusion Molecular data indicate a need to revise the classification of common eider subspecies, with birds from Shetland considered as subspecies faeroeensis. [ABSTRACT FROM AUTHOR]

Abstract: Proposals for wind farms in areas of known importance for breeding seabirds highlight the need to understand the impacts of these structures. Using an energetic modelling approach, we examine the effects of wind farms as barriers to movement on seabirds of differing morphology. Additional costs, expressed in relation to typical daily energetic expenditures, were highest per unit flight for seabirds with high wing loadings, such as cormorants. Taking species-specific differences into account, costs were relatively higher in terns, due to the high daily frequency of foraging flights. For all species, costs of extra flight to avoid a wind farm appear much less than those imposed by low food abundance or adverse weather, although such costs will be additive to these. We conclude that adopting a species-specific approach is essential when assessing the impacts of wind farms on breeding seabird populations, to fully anticipate the effects of avoidance flights. [Copyright &y& Elsevier]

Hatching asynchrony is widespread amongst animals, but no consensus has yet emerged as to why asynchronous hatching has evolved. It is generally thought to have adaptive benefits during the raising of dependent young. However, here, we considered an alternative view of hatching asynchrony in birds as a consequence of factors acting at the onset of incubation. We recorded parental nest attendance behaviour during laying using continuous records of nest temperature in herring gulls, Larus argentatus. We tested whether nest attendance during laying was related to individual factors (clutch size and diet) and whether it had consequences on fitness outcomes (hatching spread, incubation period, hatching success and chick survival). Low nest attendance was associated with small clutch size, and independent of clutch size, pairs on a more marine diet had lower nest attendance than pairs on a lower trophic level terrestrial diet, possibly due to higher foraging effort for marine food. Broods hatched more asynchronous where pairs had a lower nest attendance during laying or took longer to complete a clutch and where the last egg took longer to hatch. Low nest attendance was also related to shorter incubation periods, possibly representing a strategy of birds in poor condition to reduce the demand of incubation by reducing the length of incubation. We found that low nest attendance during laying and increasing hatching asynchrony had detrimental effects on hatching success for small eggs laid early in the laying sequence. Increasing hatching asynchrony also had a detrimental effect on the survival of the youngest sibling. In our study population, hatching asynchrony was influenced by a more complex set of factors than simply onset of incubation and appears to be constrained by circumstances at the onset of incubation rather than to be an adaptive strategy. Thus, factors acting both during offspring rearing and at the onset of incubation need to be considered for a better understanding of hatching asynchrony. [ABSTRACT FROM AUTHOR]

The article presents a study which looked at the activity patterns of albatrosses during the nonbreeding period. For this study, the researchers used data from combination geolocator-immersion loggers deployed on the wandering albatross Diomedea exulans, black-browed albatross Thalassarche melanoprhis, grey-headed albatross Thalassarche chrysostoma and light-mantled albatross Phoebetria palpebrata from South Georgia. According to them, light-maintled albatrosses were the most active at night, while grey-headed albatrosses were the most aerial and back-browed albatrosses had the shortest flight bouts during daylight.

The article discusses a study on the genetic aspect of European starlings breeding in the Azores archipelago and in mainland Europe. Results of trial polymerase chain reactions (PCR) and mitochondrial protein-coding gene sequencing showed that the gene ND2 was more variable than cytochrome-b (cyt b). There was 0.7% maximal ND2 divergence among the populations. No genetic variation among the Azores individuals was found. Also noted is the presence of common haplotypes between the Fair Isle populations and Spain, Great Britain and Norway populations.

The article presents a study which explores the diet of seabirds with particular focus on the fatty acid signatures (FAS) for an accurate information on food web and oceanographic variability. The study examines the tissue FAS in wild and captive-fed seabirds in the context of the Mediterranean marine ecosystem, as well as the FAS in the birds' adipose tissue and plasma. The feeding experiment results and the diet of the endangered wild shearwaters were also examined. The findings show that the pelagic feeding resources outweigh shearwater diet, wherein it states that the birds' diet contained a demersal element rich in 22:1n-11. The study concludes that the diet of shearwaters is often supplemented by demersal fish from fishery disposes.

Abstract: The wind power industry has grown rapidly in the UK to meet EU targets of sourcing 20% of energy from renewable sources by 2020. Although wind power is a renewable energy source, there are environmental concerns over increasing numbers of wind farm proposals and associated cumulative impacts. Individually, a wind farm, or indeed any action, may have minor effects on the environment, but collectively these may be significant, potentially greater than the sum of the individual parts acting alone. EU and UK legislation requires a cumulative impact assessment (CIA) as part of Environmental Impact Assessments (EIA). However, in the absence of detailed guidance and definitions, such assessments within EIA are rarely adequate, restricting the acquisition of basic knowledge about the cumulative impacts of wind farms on bird populations. Here we propose a conceptual framework to promote transparency in CIA through the explicit definition of impacts, actions and scales within an assessment. Our framework requires improved legislative guidance on the actions to include in assessments, and advice on the appropriate baselines against which to assess impacts. Cumulative impacts are currently considered on restricted scales (spatial and temporal) relating to individual development EIAs. We propose that benefits would be gained from elevating CIA to a strategic level, as a component of spatially explicit planning. [Copyright &y& Elsevier]

Seabird colonies provide rare opportunities to study trophic segregation in an entire bird community. We here present data on nitrogen and carbon isotope ratios of eight species of seabirds from New Island, Falkland Islands, and compare trophic levels (TL) and foraging distributions. We included adult feathers representing the interbreeding season, as well as chick feathers or down representing the breeding season. The stable isotope ratios indicated differences in feeding areas and TLs between species, consistent with the data of previous conventional diet analyses and observations at sea. We further reviewed conventional and stable isotope seabird community studies calculating the means and ranges of TLs observed across these studies. The mean TL (3.7) of the seabird community on New Island was at the lower end of the mean value range (3.5–4.5), but not significantly different, from the reviewed seabird communities. Seabirds on New Island had a range of 1.3 TLs, which is on the upper end of ranges within a community (0.4–1.5), indicating strong trophic structuring. [ABSTRACT FROM AUTHOR]

The article discusses a study on age determination of immature Black-browed and Atlantic Yellow-nosed Thalassarche chlororhvnchos albatrosses captured at sea off the Brazilian coast. The study used the bill colour, along with moult data, to describe the characteristics of birds of various ages, from fledging plumage up to adult plumage, from studies of birds captured at sea. Birds off Brazil, which originated mainly from the Falkland lslands/Malvinas, differ considerably from birds from South Georgia Island based on comparison with previous descriptions for ageing Black-browed Albatross.

The article presents the study on the individual migratory schedules and wintering areas of Morus bassanus or the Northern gannets in Bass Rock, Scotland. The study aims to determine these migratory schedules and wintering areas by distributing geolocation data loggers on the breeding adults of northern gannets. The scheme has been administered over two consecutive winters and observed how the individual bird engaged in various migratory behaviour. The result shows that individual gannets have variable migratory behaviours due to human influence on marine ecosystem.

In many sexually size-dimorphic species of birds and mammals, the larger sex, often the males, show increased environmental sensitivity during ontogeny. This is generally assumed to be due to higher energy requirements, reflected in higher absolute growth rates of the larger sex. Poor early conditions often increase the sex differences in vulnerability. However, it is not clear whether these patterns are equally pervasive in species where females are larger, as males face an additional early disadvantage due to high levels of testosterone. We investigated sex-specific growth patterns of mass, tarsus and wing of the great skua Stercorarius skua, a seabird with reversed size dimorphism. We were particularly interested in sex-specific effects of early conditions on growth. Beside data from unmanipulated nests, we present results from an egg removal experiment, which caused chicks to hatch from smaller eggs and in poorer body condition. Half of the experimental chicks were raised by pairs in which mothers were in poor body condition. At the end of the nesting period, great skua chicks exhibited a comparable degree of size dimorphism as is found in adults, although neither sex had reached final adult size. Despite females reaching larger asymptotic values of mass and tarsus, timing of growth was not different between the sexes. Absolute growth was higher for females around the time of maximum growth, which suggests that daughters face higher energetic demands. We found sex-specific effects of poor early conditions on growth patterns, although not to the extent which we had predicted. Hatching in poor body condition was related to slowed growth in females but not males. However, our experimental manipulations had no additional negative effect on growth. Our results indicate that daughters in the great skua face higher demands during growth than sons, and that early conditions are more important for the development of the larger sex in this reversed dimorphic species. [ABSTRACT FROM AUTHOR]

Masden, E. A., Haydon, D. T., Fox, A. D., Furness, R. W., Bullman, R., and Desholm, M. 2009. Barriers to movement: impacts of wind farms on migrating birds. – ICES Journal of Marine Science, 66: 746–753. Advances in technology and engineering are enhancing the contribution that wind power makes to renewable energy generation. Wind farms, both operational and in planning, can be expected to impact negatively on wildlife populations, particularly birds. We propose a novel approach to assess the impacts through the energetic costs of avoidance behaviour for a long-distance, migratory seaduck. Flight trajectories were recorded using surveillance radar at a Danish offshore wind farm with emphasis placed on the 200 000+ migrating common eiders that pass through the area annually. Minimum distance to wind farm and curvature of trajectories were compared pre- and post-construction. Additional costs of the avoidance response were estimated using an avian energetic model. The curvature of eider trajectories was greatest post-construction and within 500 m of the wind farm, with a median curvature significantly greater than pre-construction, suggesting that the birds adjusted their flight paths in the presence of the wind farm. Additional distance travelled as a consequence of the wind farm's presence was ca. 500 m and trivial compared with the total costs of a migration episode of 1400 km. However, construction of further wind farms along the migration route could have cumulative effects on the population, especially when considered in combination with other human actions. [ABSTRACT FROM PUBLISHER]

Stable isotopes of growing feathers and blood both represent assimilated diet, and both tissues are used to study the diet and foraging distribution of marine and terrestrial birds. Although most studies have assumed that both tissues represent a difference of one trophic level to diet, the enrichment factors of blood and feathers may differ, especially where endogenous reserves are used as precursors during feather synthesis. In this study, we compare carbon and nitrogen stable isotopes of blood and simultaneously growing feathers of five species of Procellariiformes, representing five genera, different geographical regions and different life stages (chicks and adults). In all species, feathers were enriched in 15N and 13C compared with blood. Isotopic values of carbon and nitrogen were correlated in different tissues growing simultaneously for most species analyzed, suggesting that mathematical corrections could be used to compare different tissues. Our results imply that more care needs to be taken when comparing stable isotope signatures across studies assuming different tissues are equivalent indicators of trophic ecology. [ABSTRACT FROM AUTHOR]

The existence of two seasonally distinct breeding populations of Oceanodroma storm-petrels in the Azores islands was first documented in 1996. The discovery of morphological differences between the populations led to the suggestion that they may represent cryptic sibling species. Recent mtDNA and microsatellite analysis from storm-petrel populations has considerably advanced our understanding of their taxonomic relationships. Here we present new information on the timing of breeding and moult of the two Azores populations, the extent of exchange of individuals between seasons, and diet from feather isotopes. We conclude that the hot-season Azores population should be considered a new species for which we propose the name Oceanodroma monteiroi, Monteiro's Storm-petrel. The species is both genetically distinct and genetically isolated from the sympatric cool-season population of Madeiran Storm-petrel Oceanodroma castro, and from all other populations of Oceanodroma castro in the Atlantic and Pacific Oceans examined to date. Differences in the vocalizations permit species recognition, and the extent of primary feather wear and stage of moult aids separation of the two species in the Azores, which is especially valuable during August when both attend the breeding colonies in large numbers. Feather carbon and nitrogen isotopes reveal that the diet of Monteiro's Storm-petrel differs from that of the sympatric Madeiran Storm-petrel during both breeding and non-breeding seasons, and unlike the Madeiran Storm-petrel, Monteiro's Storm-petrel appears to maintain the same foraging environment during the summer and winter months, though it shows a dietary shift to higher trophic levels during the non-breeding season. Monteiro's Storm-petrel is thought to be confined to the Azores archipelago, where it is currently known to nest on just two small neighbouring islets. The total population size was estimated at 250–300 pairs in 1999. [ABSTRACT FROM AUTHOR]

The artificial mussel (AM), a novel chemical sampling device, has been developed for monitoring dissolved trace metals in marine environments. The AM consists of Chelex-100 suspended in artificial seawater within Perspex tubing and enclosed with semi-permeable polyacrylamide gel at both ends. To validate the field performance of the AM in temperate waters, we deployed AMs alongside transplanted blue mussels Mytilus edulis in coastal environments in Scotland (Holy Loch, Loch Fyne, Loch Striven and Millport) and Iceland (Reykjavikurhöfn, Gufunes, South of þerney, Hofsvik, Hvalfjörður and Sandgerði) for monitoring trace metals. While uptake patterns of Cd between the AM and M. edulis were highly comparable, discrepancies were found in the accumulation profiles of the other metals (Cu, Cr, Pb and Zn), in particular Zn. Nonetheless, the AMs gave a better resolution to accurately reveal the spatial difference in dissolved metal contamination when compared with M. edulis. AMs complement the use of mussels since AMs indicate dissolved metals in seawater, whereas uptake by mussels indicates a mixture of dissolved and particulate metals. Our results also indicated that historical metal exposure of the transplanted M. edulis could significantly confound their metal concentrations especially when the deployment period was short (i.e. <34d). This study suggested that the AM can overcome problems associated with variable biological attributes and pre-exposure history in the mussel, and provides a standardized and representative time-integrated estimate of dissolved metal concentrations in different marine environments. [Copyright &y& Elsevier]

Copyright of Journal of Field Ornithology is the property of Resilience Alliance and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The abundance and availability of food are critical determininants of reproductive success and population dynamics of marine top predators. However, recent work has indicated that the quality of the food may also be critically important for some marine predators. The ‘junkfood hypothesis’ was originally suggested as a potential explanation for a dramatic population decline of Stellers sea lions Eumetopias jubatus in the Gulf of Alaska. According to the hypothesis, a dietary switch to prey of low energy content led to detrimental effects on the population of sea lions. A number of observations indicate that the hypothesis is relevant for several population parameters. Recent work on piscivorous seabirds has provided substantial evidence indicating the relevance of this hypothesis in food webs in e.g. the North Pacific, the North Sea and the Baltic Sea. The emergence of ‘junk-food’ in these systems may be coupled to large scale changes in climatological and oceanographic forcing, although predation, fishing and competition provide additional plausible hypotheses. It may be possible to predict which kinds of animals will be particularly sensitive to food quality; these seem to be species with limited ability to carry food loads, with energetically-expensive foraging behaviour, and with digestive anatomy evolved to minimize mass at the cost of digestive efficiency. This review suggests that the junk-food hypothesis is a highly relevant factor in relation to sustaining ecosystem resilience, and is an important consideration in ecosystem management. Sustaining healthy populations of marine top-predators requires an understanding of the role of food quality, in addition to food abundance and availability. [ABSTRACT FROM AUTHOR]

The largest known colony of Thin-billed prions Pachyptila belcheri has been coexisting with introduced mammals for more than 100 years. Three of the introduced mammals are potential predators of adults, eggs and chicks, namely ship rats Rattus rattus, house mice Mus musculus and feral cats Felis catus. We here determine habitat preferences over three seasons and dietary patterns of the unique set of introduced predators at New Island, Falkland Islands, with emphasis on the ship rats. Our study highlights spatial and temporal differences in the levels of interaction between predators and native seabirds. Rats and mice had a preference for areas providing cover in the form of the native tussac grass Parodiochloa flabellata or introduced gorse Ulex europaeus. Their diet differed markedly between areas, over the season and between age groups in rats. During the incubation period of the prions in November–December, ship rats had mixed diets, composed mainly of plants and mammals, while only 3% of rats had ingested birds. The proportion of ingested birds, including scavenged, increased in the prion chick-rearing period, when 60% of the rats consumed prions. We used δ13C and δ15N to compare the importance of marine-derived food between mammal species and individuals, and found that rats in all but one area took diet of partly marine origin, prions being the most frequently encountered marine food. Most house mice at New Island mainly had terrestrial diet. The stable isotope analysis of tissues with different turnover times indicated that individual rats and mice were consistent in their diet over weeks, but opportunistic in the short term. Some individuals (12% of rats and 7% of mice) were highly specialized in marine-derived food. According to the isotope ratios in a small sample of cat faeces, rodents and rabbits were the chief prey of cats at New Island. Although some individuals of all three predators supplement their terrestrial diet with marine-derived food, the current impact of predation by mammals on the large population of Thin-billed prions at New Island appears small due to a number of factors, including the small size of rodent populations and restriction mainly to small areas providing cover. [ABSTRACT FROM AUTHOR]

Birds such as great skuas Catharacta skua adapted for successful breeding at high latitudes may experience problems of heat dissipation in mild climates. Great skuas spend time bathing at freshwater sites close to breeding territories and here, we examine impacts of heat stress on bathing, foraging and nest attendance of adults during three breeding seasons with marked variation in the availability of prey (1-group sandeels Ammodytes marinus). Adults exhibited diurnal variation in bathing activity that matched heat-stress conditions. Moreover more birds bathed on days of higher average heat stress, suggesting that bathing plays a role in thermoregulation. Bathing numbers were lower in years of poor food availability, when adult attendance at territories was low, probably because lower attendance reduced the opportunity for parents to bathe without leaving chicks unattended. Chicks are normally guarded by female parents and fed by males but under conditions of low food availability territorial attendance of breeding pairs was particularly low on days of high heat stress, with chicks regularly left unattended at air temperatures exceeding 14°C. Unattended chicks are at risk of being killed by neighbouring conspecifics and survival of chicks to fledging was low in the two years of low sandeel stocks. Our study indicates that for great skuas, indirect effects of climate change on prey stocks and direct effects on heat stress experienced by adults may be additive. [ABSTRACT FROM AUTHOR]

Capsule: Siskins and Coal Tits were present in gardens more often in years of poor Sitka Spruce cone crops, with synchrony across the UK. Aims: To examine how the relative abundances of Siskins and Coal Tits in a garden in western Scotland varied annually with the size of the spruce cone crop, and to determine whether this pattern was similar nationally. Methods: A ten-year mist-netting data set from Tarbet, Argyll and Bute was used to test the hypothesis that some species utilize supplementary food in gardens more often in years with poor cone crops than in years when crops are large. Annual peaks in the relative abundances of four species (two that ate conifer seed and two that did not) in Tarbet were correlated with a Sitka Spruce masting index. BTO Garden Bird Watch data from six regions of the UK were correlated with the Tarbet data, the cone index and each other to determine the extent of synchrony. Results: Both Siskins and Coal Tits were present more often in the Tarbet garden in years with poor cone crops, with relative abundances significantly negatively correlated with cone crop for both species (r = -0.739 and -0.832, respectively). Correlations between regions using BTO data showed abundances of species in gardens to be broadly similar across the UK. Independent scores of cone abundance in Kielder and Galloway were correlated. Correlations between BTO data, cone index and Tarbet garden data were mostly high and almost all in the same direction, also indicating a degree of synchrony in cone production across the UK. Conclusion: Both Siskins and Coal Tits appear to be influenced by changes in cone abundance, switching to feed on supplementary food in gardens more often in years with few cones than in mast years. While such a relationship has been shown previously for Siskins, for Coal Tits this is a novel result. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Capsule The main factors are past and present human activities, especially the introduction of rats to islands. Aims To assess factors that influence breeding distribution and abundance of Storm-petrel. Methods We used a database for 142 islands in Shetland and Orkney. Breeding status of Storm-petrel was related to data for each island on introduced and indigenous predators, other human-related features, and aspects of island geography. Results Although 92% of the total land area of the archipelagos comprised islands with rats present, Storm-petrel colonies were almost totally restricted to rat-free islands. They also occurred more frequently on islands with cliffs, far from neighbouring islands with humans, and on islands with a low rate of human visits. Colony size was smaller on the smallest occupied islands. Breeding numbers of Great Skuas Stercorarius skua, Great Black-backed Gulls Larus marinus, and Storm-petrels all correlated, as each increased with island size. Conclusions The presence or absence of rats is the single most important influence on Storm-petrel breeding distribution in Orkney and Shetland. However, geographical and human-related effects, such as the presence of cliffs or the occurrence of human visits, also appear to influence the distribution of Storm-petrels, whereas avian predators appear to have had little effect until now. [ABSTRACT FROM AUTHOR]

Long-lived species are expected to reduce their current reproductive effort in adverse conditions in order not to jeopardize their future reproduction. Parasitic Jaegers (Stercorarius parasiticus) breeding in Shetland, United Kingdom, have declined substantially in numbers over the last 15 years, although the causes of this decline remain unclear. By carrying out a supplementary feeding experiment during the chick-rearing period, we tested the hypothesis that food availability has contributed to this decline. Data were collected on adult territory attendance, chick growth rates, and breeding success during the experimental season, and adult return rates, body condition, and laying dates during the following season. Differences in carbon and nitrogen isotope ratios in the natural and supplementary food, analyzed in the chicks' feathers, showed that chicks received one-fifth of their protein requirements from the supplementary food, but this amount varied between broods. Compared with controls, supplemented pairs showed higher attendance on the territory, improved breeding success, and higher return rate. This emphasizes that adult return rate is more sensitive to food availability than has been assumed previously. Control birds may have maintained too high a current reproductive effort at the expense of future reproduction, perhaps due to the unpredictability of their main food source, sandeels, which seemed abundant early in the season but scarce during chick rearing. This study suggests that the consequences of poor food availability are shared between offspring and parents in this species. [ABSTRACT FROM AUTHOR]

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 × 106 kJ and 546·6 × 106 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.Journal of Applied Ecology(2004)41, 1117 –1128 [ABSTRACT FROM AUTHOR]

We investigated the effects of increased egg production on body condition as well as on measures of reproductive performance in great skuas,Stercorarius skua, over two subsequent years. We experimentally increased egg production from the normal two to six eggs. Six eggs might also be produced under natural circumstances after repeated clutch loss. After the production of the last egg we measured: (i) body mass, (ii) pectoral muscle, and (iii) haematocrit, total red blood cell count and mean corpuscular volume, as indicators of body condition. We took the same measurements of control females who had produced the normal clutch of two eggs. The measurements were repeated one year after the manipulation, and survival, laying dates, clutch sizes and hatching success were recorded for up to three consecutive years. After producing six eggs, females were lighter, had smaller pectoral muscles and lower haematological values than control females. Hatching success of eggs was significantly reduced. Even one year after the experiment there were still differences in body condition. Annual survival was not affected by the manipulations, although there was an indication that survival costs depended on whether chicks were raised after the increased egg production. While pair bonds and egg sizes were not affected in the post-experimental year, females started breeding significantly later than in the previous year. Two years after the experiment laying dates had advanced again and were not different from those of control females. This pattern of maintaining survival and egg sizes, but delaying breeding in the post-experimental year was found for two independent groups of females which had both been subjected to increased egg production. These results present evidence that increased egg production can have long-term effects on female body condition and aspects of reproduction. However, although present, the costs of extra eggs appear to have been relatively small in the great skua in comparison to the two other bird species for which inter-annual effects have been reported. [ABSTRACT FROM AUTHOR]

Copyright of Condor is the property of Oxford University Press / USA and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is clear that discards from commercial fisheries are a key food resource for many seabird species around the world. But predicting the response of seabird communities to changes in discard rates is problematic and requires historical data to elucidate the confounding effects of other, more ‘natural’ ecological processes. In the North Sea, declining stocks, changes in technical measures, changes in population structure and the establishment of a recovery programme for cod (Gadus morhua) will alter the amount of fish discarded. This region also supports internationally important populations of seabirds, some of which feed extensively, but facultatively, on discards, in particular on undersized haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus). Here we use long-term data sets from the northern North Sea to show that there is a direct link between discard availability and discard use by a generalist predator and scavenger-the great skua (Stercorarius skua). Reduced rates of discarding, particularly when coupled with reduced availability of small shoaling pelagic fish such as sandeel (Ammodytes marinus), result in an increase in predation by great skuas on other birds. This switching of prey by a facultative scavenger presents a potentially serious threat to some seabird communities. [ABSTRACT FROM AUTHOR]

Evidence from mtDNA suggests that two skuas, one discovered in the Scilly Islands Cornwall in October 2001, the other in Glamorgan in February 2002, belong to the Brown Skua groupCatharacta antarctica– a species not previously recorded in the North Atlantic. These molecular data do not exclude the possibility of either bird being a hybrid between Brown Skua and South Polar SkuaC. maccormicki, but population estimates suggest that this is unlikely. More importantly, biometrics show that the Glamorgan bird is much smaller than hybrids but matches Falkland SkuaC. a. antarctica. The distributions ofC. antarcticasubspecies at sea are not well known, but the discovery of two of these birds in the UK suggests that they may wander more extensively than previously thought. [ABSTRACT FROM AUTHOR]

Several different techniques have been used to study the diet composition of skuas and gulls in polar regions. In this study, we assessed the diet of great skuas using five techniques (pellets, prey remains, spontaneous regurgitates, observed feeds and water off-loading). The estimates of diet derived from each sampling technique during a single breeding season were generally similar. Although it is easy to collect large samples of pellets and remains, these over-estimate the amount of indigestible material in the diet. Prey remains provide a high degree of taxonomic accuracy, but may under-estimate prey swallowed whole. Water off-loading provides unbiased estimates of chick diet but only during a short period in the breeding season. It may also stress birds, and is labour-intensive. Spontaneous regurgitates are useful for assessing chick and adult diet but are difficult to collect systematically, and differing prey digestibility may bias results. Observed feeds are time consuming to record and over-represent easily identifiable prey. Technique-dependent biases highlight that sampling methods should be selected on the basis of sample sizes, time, taxonomic detail and age of study birds. Biomass may be estimated using pellets with correction factors, and also spontaneous regurgitates and water off-loading, but prey remains and observed feeds may be more inaccurate. [ABSTRACT FROM AUTHOR]

Examines the influence of food availability and predation on the survival of Kittiwakes in Shetland, Scotland. Environmental factors reducing the fecundity of the Kittiwakes breeding; Explanations for the decline in the metapopulation of the animals; Details on the food supply and breeding success of the animals.

By switching great skuas Catharacta skua from one isotopically distinct diet to another, we measured diet-tissue discrimination factors and tested the assumption that dietary nitrogen and carbon isotope signatures are incorporated into blood and feathers at similar rates. We also examined the effects of metabolic rate and looked for evidence of isotopic routing. We found that blood δ[sup15]N and δ[sup13]C signatures altered after the diet swish at similar rates (14.4 d and 15.7 d, respectively). Qualitative analyses imply that the same was true with feathers. Mass balance calculations suggest that only a small amount of lipid is likely to be involved in the synthesis of Mood and feathers. Differences in diet-tissue discrimination factors before and after the diet switch may mean that toward the end of the experiment, some of the nutrients for blood synthesis had been coming from stores. Repeated measures mixed models provided evidence that increases in metabolic rate might accelerate fractional turnover rates in blood. There is a need for more laboratory-based experimental isotope studies in order to address further questions that this study has raised. [ABSTRACT FROM AUTHOR]

The lesser sandeel, Ammodytes marinus, is a key food for many seabirds and seals, and is also the target of the largest single-species fishery in the North Sea. Despite claims that sandeel fishing has harmed dependent predator populations, census data show that most seabirds and grey seals increased in numbers as the fishery grew and reached peak harvest. Generally high breeding success of black-legged kittiwakes at North Sea colonies also suggests that sandeel abundance has remained good for breeding seabirds at the broad scale, though local and small-scale effects of sandeel fishing should not be overlooked. VPA and CPUE data suggest that abundance increased as the fishery grew. A negative correlation between sandeel recruitment and total stock size preceding spawning suggests that there is now resource competition (bottom-up control). Bioenergetics modelling indicates that predatory fish take far more sandeel than taken by the industrial fishery or wildlife. Effects of decreases in predatory fish stocks have been greater than increases in the take by seabirds and seals and by the fishery. Thus, overall, there appears to have been a reduction in mortality during the last 30 years. Changes in predatory fish abundances, especially mackerel and whiting, may influence sandeel stocks more than changes in industrial fishery, at least at the scale of the North Sea as a whole. These interactions imply that seabird and seal food supply in terms of sandeel may be strongly dependent on decisions regarding management of stocks of mackerel and gadoids. The overwhelming influence of predation on “food-fish” by predatory fish may be a feature of many marine food webs worldwide, where “fishing down the food web” has occurred, and this has clear management implications if wildlife and fisheries are to coexist. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]

Assesses the use of pellets as indicators of diet in great skuas in Scotland. Comparison with other methods of sampling skua diet; Factors contributing to differences in pellet production; Pellet production per meal.

Presents information on a study which assessed the diet of breeding Great Skuas in Great Britain. Methodology; Results and discussion.

Examines the kinetics, dose-response, and excretion of methylmercury in free-living adult Cory's shearwaters. Kinetics of methylmercury in blood; Comparison of blood mercury concentrations measured at various times after dose administration in early May for each dose by sex; Partition coefficients.

We present data on digestive efficiencies and gut retention times of eight North Atlantic seabird species, fed on two fish species -- lesser sandeel Ammodytes marinus and whiting Merlangius merlangus -- which commonly occur in the diet of wild seabirds. In an interspecific comparison, there was a positive relationship between retention time and digestive efficiency, which we suggest represents a trade-off between conflicting benefits of efficient digestion and rapid digestion. Analysis of excretion curves revealed that retention time of digesta in the stomach was more important than passage time of digesta through the intestine in determining whole gut retention time Differences in stomach retention time of lesser sandeel and whiting explained the longer overall retention time of the latter diet. Stomach relention time and whole gut retention time were greater in species with relatively large stomachs, while intestine passage time was correlated with relative intestine length. Species which typically eat a wide range of food types, including low quality items, tended to have slow and efficient digestion and heavy stomachs. whereas species which specialise on readily digestible and energy dense food types had the opposite digestion strategy. [ABSTRACT FROM AUTHOR]

Territorial or nest attendance by adult breeding seabirds is often essential to prevent egg or chick mortality. As a result, parent birds, when not engaged in foraging trips, should stay on their territories whenever there is a risk from leaving their eggs and chicks unattended. Differences in territorial attendance and time spent foraging by birds of different ages have been interpreted as resulting from differences in adult foraging ability or in motivation to invest in the current reproductive attempt. However, most studies have failed to take into account seasonal variations in food availability, which could affect these patterns, because timing of breeding is often dependent on adult age. We designed an experiment to investigate the levels of territorial attendance displayed by Great Skuas of known age facing the same environmental conditions and with similar food requirements. This was achieved by manipulating clutches so that all study pairs hatched their chicks at the same time. Pairs with one chick had a higher attendance (mean number of adults per territory) than pairs with two chicks. This suggests that the need to increase the time foraging in response to the nutritional demands of a larger brood overrides any effect due to differential motivations in the amount of parental effort to be invested in brood protection. Pairs with older males had a higher attendance than pairs with younger males. About 61% of the estimated foraging time of the pairs fell on the males. Attendance and adult age were not correlated with chick body condition. We conclude that pairs with two chicks that had high attendance achieved this by being more efficient foragers, and not by provisioning their chicks less well. Therefore, our results suggests that older males are better foragers than younger birds. Female age did not correlate with attendance levels. However, pairs with older females were less likely to leave their chicks unattended, which suggests that those pairs had... [ABSTRACT FROM AUTHOR]

1. The numbers of cormorants Phalacrocorax carbo feeding at English freshwater fisheries during winter have increased rapidly over the last 20 years, causing concern among fishery managers and anglers. 2. In order to assess the extent of freshwater feeding, stable isotope ratios of carbon and nitrogen (δ13 C and δ15 N) in feathers of wild cormorants from inland freshwater fisheries were compared with those in the feathers of piscivorous birds with marine diets (captive ‘marine-fed’ cormorants, free-ranging shags Phalacrocorax aristotelis ) and freshwater diets (juvenile goosanders Mergus merganser ). 3. Isotope signatures of feathers represent the diet at the time of growth. Feathers grown at different times of the year were taken from wild cormorants; each feather type therefore represented the diet over a different temporal scale. 4. Isotopic analyses of feathers indicated that, when shot, nearly all of the cormorants had been feeding entirely on freshwater prey. The mean δ13 C value of primary feathers growing when birds were shot was –22·2‰, indicative of an entirely freshwater diet. 5. The move to freshwater habitats from coastal breeding grounds occurred over several months, but once established cormorants appear to have fed at freshwater sites throughout the autumn and winter. 6. The suitability of using a two-source isotopic mixing model in order to quantify the extent of freshwater feeding in piscivorous birds is discussed. 7. Although the results indicate long-term residency and feeding in freshwater systems, they do not indicate whether birds were feeding regularly at the sites at which they were shot, or the composition of the diet. It is recommended that further studies using telemetry and multiple isotope analyses be carried out in order to address these issues. [ABSTRACT FROM AUTHOR]

Discusses the influences of breeding experience on the reproductive performance of great skuas Catharacta skua on Foula, Shetland in Scotland. Factors for increases in clutch size, a-egg volume and hatching; Association of increase in breeding performance to experience.

Measures the field metabolic rate of nesting Northern Fulmars using the doubly labeled water technique. Behavior of labeled birds; At-sea metabolism; Effects of win on FMR; Wingbeat frequency.

Presents the study of copulation behavior and territorial intrusions in the great skua. Description of the great skua; Information on the copulation process; Indepth look at the study.

Presents a study regarding the high levels of nonbreeding by experienced Great Skuas (Catharacta skua), and Parasitic Jaegers on Foula, Shetland Islands, in Scotland. Methods used to conduct the study; Correlation between environmental conditions and the incidence of nonbreeding at the population level; Results of the study.

Investigates the effect of hatching date on chick body condition, chick survival, post-fledgling survival and eventual breeding performance among adult great skuas Catharacta skua on Foula, Shetland in Scotland. Survival of chicks in early broods; Annual variation in the seasonal pattern of chick growth and survival.