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Sarah Wanless - One of the best experts on this subject based on the ideXlab platform.
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the importance of observer effort on the accuracy of breeding success estimates in the common guillemot Uria aalge
Bird Study, 2020Co-Authors: M P Harris, Sarah Wanless, Martin Heubeck, Maria I Bogdanova, Mark Newell, Francis DauntAbstract:Capsule: A data-thinning approach was used to assess the effects of reducing the frequency of nest-checks on estimates of breeding success of Common Guillemots Uria aalge. Inter-year and inter-colo...
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age related effects on breeding phenology and success of common guillemots Uria aalge at a north sea colony
Bird Study, 2016Co-Authors: M P Harris, S D Albon, Sarah WanlessAbstract:ABSTRACTCapsule: Common Guillemots Uria aalge show delayed breeding and marked age-related changes in reproductive success consistent with improved performance with experience.Aims: To determine age of first breeding and age-related effects on breeding phenology and success of Common Guillemots.Methods: Resighting data from a long-term colour-ringing study of Common Guillemot chicks were combined with observations of breeding phenology and success to follow the recruitment process, breeding phenology and success of 62 birds at a major North Sea colony over a 30-year period.Results: The median age of first breeding of Common Guillemots was 6.6 years. There were no detectable costs of first breeding on return rates or the likelihood of breeding the next season but first time breeders bred later and less successfully. Age of first breeding and lifetime breeding success both varied among individuals but there was no clear optimal age of first breeding and early first breeding was not associated with higher li...
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The visual fields of Common Guillemots Uria aalge and Atlantic Puffins Fratercula arctica: foraging, vigilance and collision vulnerability
Ibis, 2015Co-Authors: Graham R. Martin, Sarah WanlessAbstract:Significant differences in avian visual fields are found between closely related species that differ in their foraging technique. We report marked differences in the visual fields of two auk species. In air, Common Guillemots Uria aalge have relatively narrow binocular fields typical of those found in non-passerine predatory birds. Atlantic Puffins Fratercula arctica have much broader binocular fields similar to those that have hitherto been recorded in passerines and in a penguin. In water, visual fields narrow considerably and binocularity in the direction of the bill is probably abolished in both auk species. Although perceptual challenges associated with foraging are similar in both species during the breeding season, when they are piscivorous, Puffins (but not Guillemots) face more exacting perceptual challenges when foraging at other times, when they take a high proportion of small invertebrate prey. Capturing this prey probably requires more accurate, visually guided bill placement and we argue that this is met by the Puffin's broader binocular field, which is retained upon immersion; its upward orientation may enable prey to be seen in silhouette. These visual field configurations have potentially important consequences that render these birds vulnerable to collision with human artefacts underwater, but not in air. They also have consequences for vigilance behaviour.
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the need for year specific correction factors k values when converting counts of individual common guillemots Uria aalge to breeding pairs
Bird Study, 2015Co-Authors: M P Harris, Martin Heubeck, Mark Newell, Sarah WanlessAbstract:Capsule Long-term studies at two Scottish colonies show that the k value used to convert counts of individual Common Guillemots Uria aalge to pairs has changed substantially in the last 15 years due to decreases in survival and colony attendance. Any future wide-scale census of this species needs to collect concurrent k values if counts of individual birds are to be used to determine changes in breeding populations since the previous survey.
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among colony synchrony in the survival of common guillemots Uria aalge reflects shared wintering areas
Ibis, 2011Co-Authors: Toby J Reynolds, M P Harris, Ruth King, R L Swann, David C Jardine, Morten Frederiksen, Sarah WanlessAbstract:Spatiotemporal variation in survival may be an important driver of multi-population dynamics in many wild animal species, yet few scientific studies have addressed this issue, primarily due to a lack of sufficiently comprehensive and detailed datasets. Synchrony in survival rates among different, often distant, subpopulations appears to be common, caused by spatially correlated environmental conditions or by movement of animals from different sites such that their ranges overlap. Many seabird populations are effectively isolated during the breeding season because colonies are widely separated, but over the winter, birds disperse widely and there may be much mixing between different populations. The non-breeding season is also the period of main mortality for seabirds. Using mark–recapture and ring-recovery data, we tested for spatial, temporal and age-related correlations in survival of Common Guillemots Uria aalge among three widely separated Scottish colonies that have varying overlap in their overwintering distributions. Survival was highly correlated over time for colonies/age-classes sharing wintering areas and, except in 2004, was essentially uncorrelated for those with separate wintering areas. These results strongly suggest that one or more aspects of the winter environment are responsible for spatiotemporal variation in survival of British Guillemots, and provide insight into the factors driving large-scale population dynamics of the species.
M P Harris - One of the best experts on this subject based on the ideXlab platform.
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the importance of observer effort on the accuracy of breeding success estimates in the common guillemot Uria aalge
Bird Study, 2020Co-Authors: M P Harris, Sarah Wanless, Martin Heubeck, Maria I Bogdanova, Mark Newell, Francis DauntAbstract:Capsule: A data-thinning approach was used to assess the effects of reducing the frequency of nest-checks on estimates of breeding success of Common Guillemots Uria aalge. Inter-year and inter-colo...
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age related effects on breeding phenology and success of common guillemots Uria aalge at a north sea colony
Bird Study, 2016Co-Authors: M P Harris, S D Albon, Sarah WanlessAbstract:ABSTRACTCapsule: Common Guillemots Uria aalge show delayed breeding and marked age-related changes in reproductive success consistent with improved performance with experience.Aims: To determine age of first breeding and age-related effects on breeding phenology and success of Common Guillemots.Methods: Resighting data from a long-term colour-ringing study of Common Guillemot chicks were combined with observations of breeding phenology and success to follow the recruitment process, breeding phenology and success of 62 birds at a major North Sea colony over a 30-year period.Results: The median age of first breeding of Common Guillemots was 6.6 years. There were no detectable costs of first breeding on return rates or the likelihood of breeding the next season but first time breeders bred later and less successfully. Age of first breeding and lifetime breeding success both varied among individuals but there was no clear optimal age of first breeding and early first breeding was not associated with higher li...
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the need for year specific correction factors k values when converting counts of individual common guillemots Uria aalge to breeding pairs
Bird Study, 2015Co-Authors: M P Harris, Martin Heubeck, Mark Newell, Sarah WanlessAbstract:Capsule Long-term studies at two Scottish colonies show that the k value used to convert counts of individual Common Guillemots Uria aalge to pairs has changed substantially in the last 15 years due to decreases in survival and colony attendance. Any future wide-scale census of this species needs to collect concurrent k values if counts of individual birds are to be used to determine changes in breeding populations since the previous survey.
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among colony synchrony in the survival of common guillemots Uria aalge reflects shared wintering areas
Ibis, 2011Co-Authors: Toby J Reynolds, M P Harris, Ruth King, R L Swann, David C Jardine, Morten Frederiksen, Sarah WanlessAbstract:Spatiotemporal variation in survival may be an important driver of multi-population dynamics in many wild animal species, yet few scientific studies have addressed this issue, primarily due to a lack of sufficiently comprehensive and detailed datasets. Synchrony in survival rates among different, often distant, subpopulations appears to be common, caused by spatially correlated environmental conditions or by movement of animals from different sites such that their ranges overlap. Many seabird populations are effectively isolated during the breeding season because colonies are widely separated, but over the winter, birds disperse widely and there may be much mixing between different populations. The non-breeding season is also the period of main mortality for seabirds. Using mark–recapture and ring-recovery data, we tested for spatial, temporal and age-related correlations in survival of Common Guillemots Uria aalge among three widely separated Scottish colonies that have varying overlap in their overwintering distributions. Survival was highly correlated over time for colonies/age-classes sharing wintering areas and, except in 2004, was essentially uncorrelated for those with separate wintering areas. These results strongly suggest that one or more aspects of the winter environment are responsible for spatiotemporal variation in survival of British Guillemots, and provide insight into the factors driving large-scale population dynamics of the species.
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site use and fidelity in the common guillemot Uria aalge
Ibis, 2008Co-Authors: M P Harris, Sarah Wanless, T R BartonAbstract:The site fidelity of 470 colour-ringed Common Guillemots Uria aalge with at least 1 year of breeding experience was followed on the Isle of May from 1982 to 1993. On average, 85.7% of birds recorded breeding at a site in any year were present at the same site in the following season. Of those which did not retain their site, 35% had moved to another site, 25% were nonbreeders and 40% were not seen. Site- fidelity of birds which returned to the colony the next year was 91%. There were no significant age or sex effects, but there were significant (and unexplained) year and area effects. Most birds which changed sites moved less than 2 m. Some birds which obtained a new site improved their nesting success, but many others became nonbreeders; it is speculated that the former chose to move site, whilst the latter had been evicted.
Robert T Barrett - One of the best experts on this subject based on the ideXlab platform.
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Environmental variability and fledging body mass of Common Guillemot Uria aalge chicks
Marine Biology, 2013Co-Authors: Robert T Barrett, Kjell Einar ErikstadAbstract:To gain a better understanding of population processes and in the light of the critically endangered status of the Common Guillemot Uria aalge in Norway, we investigate which environmental factors might affect the fitness of guillemot chicks as they depart from the nest site over a 16-year period on a colony in NE Norway. Although prey composition did not seem to influence the fledging body mass of the chicks, there were significant relationships between the yearly variations in chick body mass and abundance of two important prey species (1-group herring Clupea harengus that is an important chick food item and 0-group cod Gadus morhua that is an important adult food item), population size and the sea surface temperature around the colony. The positive influence of young herring and cod on Common Guillemot chick mass occurred during a period of warming in the Barents Sea such that future recruitment into the population will depend partly on the long-term changes in ocean climate in the region.
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seabird fish interactions the fall and rise of a common guillemot Uria aalge population
Marine Ecology Progress Series, 2013Co-Authors: Kjell Einar Erikstad, Robert T Barrett, Tone Kristin Reiertsen, Frode Vikebo, Hanno SandvikAbstract:A major challenge in population ecology is the prediction of population responses to environmental variance. Food availability has long been hypothesized to play a major role in regulating seabird populations. In general, seabirds feed on small pelagic fish and/or young age classes of larger predatory fish. Here we used a logistic population model to predict the temporal variation in the population size of common guillemots Uria aalge in a colony in NE Norway (Hornoya) between 1987 and 2011 in relation to the variation in abundance (acoustic and trawl surveys) of important fish prey species in the Barents Sea. The fish species considered, all of which have been described in the diet of common guillemot chicks and adults on Hornoya, were capelin Mallotus villosus (all age classes), 1-group herring Clupea harengus and 0-group cod Gadus morhua. The guillemot population collapsed by more than 80% during the winter 1986/1987, when the abundance indices of all fish prey species were very low, but has since steadily in - creased. The annual variation in population growth rate after the population collapse could best be explained by the variation in abundance of 0-group cod (unlagged), and the 0-group cod and capelin 6 and 4 yr earlier, respectively (equalling the age of maturation of guillemots). We also present a numerical ocean model to identify mechanisms affecting spatio-temporal prey availabil- ity of 0-group cod around the colony during the breeding season. These results undermine earlier focus on the capelin stock as the main cause of the population crash in common guillemots.
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climate fluctuations and differential survival of bridled and non bridled common guillemots Uria aalge
Ecosphere, 2012Co-Authors: Tone Kristin Reiertsen, Robert T Barrett, Kjell Einar Erikstad, Hanno Sandvik, Nigel G YoccozAbstract:Climate fluctuations and its effects on ecological processes are evident in most areas worldwide but whether such climatic effects are induced phenotypic plasticity or whether animals adapt to the new environment through micro-evolutionary processes is poorly known. In this study we have analyzed long-term data (22 years) on the relationship between climatic fluctuations and the adult survival of two distinct genetic morphs of the Common Guillemot (Uria aalge) breeding in a colony in the southern Barents Sea. In the North Atlantic, the Common Guillemot is a genetic color dimorphic species, with a non-bridled morph, with an entirely black or dark brown head, and a bridled morph having a white eye ring and auricular groove sloping back from the eye. Our results show that the two morphs responded differently to variation in the Barents Sea winter sea-surface temperature (SST). The survival rate of the bridled morph was negatively correlated to the winter SST in the Barents Sea, while that of the non-bridled morph was slightly positively correlated to the same parameter. Over the whole study period, SSTs fluctuated between warm and cold winters and the overall mean survival rates of the two morphs remained similar (96.2% and 95.9% for the bridled and non-bridled morph, respectively). This suggests a balanced selection and a stable dimorphism of the two morphs over this time period. The contrasting trends in the survival of the two morphs with respect to temperature suggest that further warming of the sea may induce directional changes and alter the frequency of the two morphs.
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optimal foraging in chick raising common guillemots Uria aalge
Journal of Ornithology, 2011Co-Authors: Julie Bugge, Robert T Barrett, Torstein PedersenAbstract:The Norwegian population of the Common Guillemot Uria aalge has declined by >95% since the 1960s, and is classified as critically endangered in the Norwegian Red List. Much of the recent decline has been attributed to reduced food availability, but without extensive documentation of adult diet. Instead, chick diet has been considered a proxy of adult diet during the breeding season in many Norwegian studies. However, central-place foraging theory, especially for single-prey loaders, predicts that this may not be so, and this study directly compares the diet of adult and chick Common Guillemots during the breeding season at a colony in NE Norway. Whereas chicks were fed mainly capelin (Mallotus villosus) and sandeels (Ammodytes sp.), most of the adult diet consisted of the two youngest year classes of Gadidae, probably cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). A successful ecosystem management of seabirds is dependent on a full understanding of how prey quality, abundance and availability influence seabird populations and their viability, such that knowing the true diet of adult Common Guillemots has important implications in the modelling and management of the Norwegian populations.
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status of black legged kittiwakes rissa tridactyla common guillemots Uria aalge and brunnich s guillemots u lomvia in murman north west russia and varanger north east norway
Polar Research, 2007Co-Authors: Yuri V Krasnov, Robert T Barrett, Natalie G NikolaevaAbstract:Recent published estimates of the numbers of seabirds breeding along the coast of Murman have been partly based on data collected in the 1960s. Counts made in some of the largest colonies in 1999–2005 show that the present populations of black-legged kittiwakes ( Rissa tridactyla ), common guillemots ( Uria aalge ) and Brunnich’s guillemot ( U. lomvia ) in Murman are approximately 110 000 pairs, 10 000–12 000 pairs and 2000–3000 pairs, respectively. In Varanger the numbers are ca. 32 000 pairs, 6000–7000 pairs and 400–500 pairs, respectively. Although there has been a large decline in black-legged kittiwake numbers in the Varanger region since 1980, there is no evidence of a similar decline in Murman at least until 1999. With the exception of one colony in Murman, numbers of common guillemots breeding throughout the region seem to have recovered after suffering a huge decline in 1986/87.
Kjell Einar Erikstad - One of the best experts on this subject based on the ideXlab platform.
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differential breeding investment in bridled and non bridled common guillemots Uria aalge morph of the partner matters
Behavioral Ecology and Sociobiology, 2014Co-Authors: Ditte Lyngbo Kristensen, Kjell Einar Erikstad, Tone Kristin Reiertsen, Truls MoumAbstract:Polymorphism is the coexistence of two or more phenotypically distinct and genetically determinate forms in a population and implies a selective balance between the alternative morphs to permanently exist. Common guillemots Uria aalge occur in two genetically distinct morphs—a non-bridled and a bridled—the latter with white eye rings and a well-defined stripe behind the eyes. In this study, we investigated differences between the morphs with regard to reproductive parameters. We used a detailed family-based sample providing data on mother, father, and chick over three breeding seasons. The mating between morphs was random but pure non-bridled and pure bridled pairs produced smaller chicks at age 15 days than the two mixed pair compositions. Body mass of the adults showed much the same pattern; pure pairs having lower body mass than mixed pairs. There were no differences between the two morphs in reproductive parameters without considering the morph of the partner. This suggests that reproductive decisions in some way not only depend on the morph but also on the tactic of the partner. Different reproductive strategies between morph family groups as found in this study may contribute to the understanding of the existence of a balanced polymorphism in common guillemots. The overall breeding conditions during the years of this study were good. However, over time in a variable environment, we suggest that tactics of different family groups may have different success stabilizing the frequency of non-bridled and bridled birds over time.
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Environmental variability and fledging body mass of Common Guillemot Uria aalge chicks
Marine Biology, 2013Co-Authors: Robert T Barrett, Kjell Einar ErikstadAbstract:To gain a better understanding of population processes and in the light of the critically endangered status of the Common Guillemot Uria aalge in Norway, we investigate which environmental factors might affect the fitness of guillemot chicks as they depart from the nest site over a 16-year period on a colony in NE Norway. Although prey composition did not seem to influence the fledging body mass of the chicks, there were significant relationships between the yearly variations in chick body mass and abundance of two important prey species (1-group herring Clupea harengus that is an important chick food item and 0-group cod Gadus morhua that is an important adult food item), population size and the sea surface temperature around the colony. The positive influence of young herring and cod on Common Guillemot chick mass occurred during a period of warming in the Barents Sea such that future recruitment into the population will depend partly on the long-term changes in ocean climate in the region.
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seabird fish interactions the fall and rise of a common guillemot Uria aalge population
Marine Ecology Progress Series, 2013Co-Authors: Kjell Einar Erikstad, Robert T Barrett, Tone Kristin Reiertsen, Frode Vikebo, Hanno SandvikAbstract:A major challenge in population ecology is the prediction of population responses to environmental variance. Food availability has long been hypothesized to play a major role in regulating seabird populations. In general, seabirds feed on small pelagic fish and/or young age classes of larger predatory fish. Here we used a logistic population model to predict the temporal variation in the population size of common guillemots Uria aalge in a colony in NE Norway (Hornoya) between 1987 and 2011 in relation to the variation in abundance (acoustic and trawl surveys) of important fish prey species in the Barents Sea. The fish species considered, all of which have been described in the diet of common guillemot chicks and adults on Hornoya, were capelin Mallotus villosus (all age classes), 1-group herring Clupea harengus and 0-group cod Gadus morhua. The guillemot population collapsed by more than 80% during the winter 1986/1987, when the abundance indices of all fish prey species were very low, but has since steadily in - creased. The annual variation in population growth rate after the population collapse could best be explained by the variation in abundance of 0-group cod (unlagged), and the 0-group cod and capelin 6 and 4 yr earlier, respectively (equalling the age of maturation of guillemots). We also present a numerical ocean model to identify mechanisms affecting spatio-temporal prey availabil- ity of 0-group cod around the colony during the breeding season. These results undermine earlier focus on the capelin stock as the main cause of the population crash in common guillemots.
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climate fluctuations and differential survival of bridled and non bridled common guillemots Uria aalge
Ecosphere, 2012Co-Authors: Tone Kristin Reiertsen, Robert T Barrett, Kjell Einar Erikstad, Hanno Sandvik, Nigel G YoccozAbstract:Climate fluctuations and its effects on ecological processes are evident in most areas worldwide but whether such climatic effects are induced phenotypic plasticity or whether animals adapt to the new environment through micro-evolutionary processes is poorly known. In this study we have analyzed long-term data (22 years) on the relationship between climatic fluctuations and the adult survival of two distinct genetic morphs of the Common Guillemot (Uria aalge) breeding in a colony in the southern Barents Sea. In the North Atlantic, the Common Guillemot is a genetic color dimorphic species, with a non-bridled morph, with an entirely black or dark brown head, and a bridled morph having a white eye ring and auricular groove sloping back from the eye. Our results show that the two morphs responded differently to variation in the Barents Sea winter sea-surface temperature (SST). The survival rate of the bridled morph was negatively correlated to the winter SST in the Barents Sea, while that of the non-bridled morph was slightly positively correlated to the same parameter. Over the whole study period, SSTs fluctuated between warm and cold winters and the overall mean survival rates of the two morphs remained similar (96.2% and 95.9% for the bridled and non-bridled morph, respectively). This suggests a balanced selection and a stable dimorphism of the two morphs over this time period. The contrasting trends in the survival of the two morphs with respect to temperature suggest that further warming of the sea may induce directional changes and alter the frequency of the two morphs.
Olof Olsson - One of the best experts on this subject based on the ideXlab platform.
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bayesian immature survival analysis of the largest colony of common murre Uria aalge in the baltic sea
Waterbirds, 2019Co-Authors: Blanca Sarzo, Carmen Armero, David Conesa, Jonas Hentatisundberg, Olof OlssonAbstract:In long-lived species, such as seabirds, immature survival is the most important life history parameter after adult survival. The assessment of immature survival has often been difficult due to extended periods in which young birds remain unobservable at sea. This study presents results on survival of immature Common Murre (Uria aalge) obtained from an extensive mark-recapture study of a large colony at Stora Karlso in the Baltic Sea, Sweden. This colony, in contrast with other colonies, has the unique feature that many 1-year-old birds return to the colony (12%). Between 2006 and 2016, 28,930 chicks were marked at fledging, of which 5,493 individuals were later resighted in the colony. Annual survival and recapture probabilities were estimated using Bayesian Cormack-Jolly-Seber models with four age classes for survival probability, and recapture probability being age and time dependent. Informative prior distributions were used to correct partial observability problems in older age classes (observed at breeding ledges). The estimated survival probability of 1-year-old birds was 0.53 (95% CI = 0.49-0.58), 2-year-old birds was 0.87 (0.79-0.96), 3-year-old birds was 0.96 (0.90-0.99), and 4-to-10-year old bird survival probability was 0.63 (0.61-0.64). Survival estimates for younger age classes were consistent with previous studies. Several biological factors may contribute to the observed decline in survival for older age classes.
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Population trends and status of four seabird species (Uria aalge, Alca torda, Larus fuscus, Larus argentatus) at Stora Karlsö in the Baltic Sea
Ornis Svecica, 2017Co-Authors: Olof Olsson, Jonas Hentati-sundbergAbstract:The island of Stora Karlsö hosts the largest colonies of fish-eating seabirds in the Baltic Sea. However, recent and reliable estimates of the number of breeding pairs of the main species have been missing. Based on a complete census in 2014, we estimated the number of Common Guillemots Uria aalge to 15,700 pairs, more than half (up to 70%) of the Baltic Sea population. The number has almost tripled since the early 1970s and the increase has been particularly strong the last 11 years, with an annual increase of 5.1%. We counted 24,600 individual adult Razorbills Alca torda and estimated it to correspond to a maximum of 12,300 pairs in 2015–2016 (census over two seasons). The colony has grown strongly; on average by 5.6% annually since the early 1970s, and Stora Karlsö now hosts up to 30% of the Baltic Sea population. Stora Karlsö also hosts colonies with about 300 pairs each of Lesser Black-backed Gull Larus fuscus and Herring Gull Larus argentatus. The gulls’ trends are negative, with an average annual decline the last 10-year period by 5.0% and 6.2%, respectively.
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adult survival and avian cholera in common guillemots Uria aalge in the baltic sea
Ibis, 2004Co-Authors: Henrik Osterblom, Henk P Van Der Jeugd, Olof OlssonAbstract:An influence at one trophic level can result in dynamic impacts also on other components of a food web. These dynamics are known as trophic cascades, and can be both top-down and bottom-up. After a near-collapse of the Baltic cod Gadus morhua stock in the 1980s, its main prey sprat Sprattus sprattus increased dramatically. The main food of sprat, marine copepods, decreased during the same time period, likely a combined effect of increased predation pressure from sprat and decreasing salinities. This shortage of food for sprat resulted in decreasing quality of sprat as a food source for common guillemots Uria aalge. However, a recent increase in fishing for sprat has again resulted in better feeding conditions for guillemots.Human impacts on this simple food web can be complex. In the early 20th century, marine mammals were abundant and nutrient levels were low in the Baltic Sea. This thesis illustrate that this situation corresponded to lower fish biomass. A reduction of seals early in the century led to reduced top-down control, which resulted in increasing fish stocks. Later, in the 1950s, the largest inflow of salt water during the century mobilized accumulated phosphorus from the deep sediments, which stimulated nitrogen fixation. Combined with increasing anthropogenic nutrient loads, this led to increased primary production and a rapid change from an oligotrophic to a eutrophicated state. This change can be termed a regime shift, which also stimulated fish production. Subsequent over-fishing of cod likely caused a second regime shift, from a cod- to a clupeid- dominated state, which led to the described effects on the common guillemots.Several factors affect the life-history of this long-lived seabird. Bycatches in gillnet fisheries is one factor directly affecting guillemot survival, and the proportion of bycatches increased during a period of increasing fishing effort. Surprisingly, avian cholera, a previously undocumented disease in common guillemots, was found at times to cause considerable adult mortality. Common guillemot life-history information can communicate the diversity of factors influencing marine ecosystems – hopefully this can increase our understanding of how complex even "simple" food webs are.
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bycatches of common guillemot Uria aalge in the baltic sea gillnet fishery
Biological Conservation, 2002Co-Authors: Henrik Osterblom, Thord Fransson, Olof OlssonAbstract:Abstract Bycatch of common guillemots (Uria aalge) appears to be the single most serious threat to the population, and the proportion of recoveries of ringed birds in fishing gear, compared with other finding circumstances, has significantly increased during a 28 year period (P
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changes in feeding behaviour and reproductive success in the common guillemot Uria aalge on the island of stora karlso
2002Co-Authors: Henrik Osterblom, Olof OlssonAbstract:We studied the feeding behaviour and reproductive success in Common Guillemots Uria aalge at the island of Stora Karlso to reveal effects of an increased density of the prey fish Sprat Sprattus sprattus. Feeding rates were almost twice as high in 1998 (4.3 feeds/chick/day) as in 1975 (2.2 feeds/chick/day), and feeding trips were short. The adult birds spent a large proportion of the day together at the site during the chick‐rearing period, indicating that the birds were not under significant food stress. Contrary to what we had expected, reproductive success was lower in 1998 and 1999 (0.671, SE = ±0.045, n = 2) than in 1974‐1977 (0.803, SE = ±0.010, n = 4) and chick survival and age at fledging was unchanged despite the increase of available Received 17 October 2001, Accepted 11 January 2002, Editor: A. Hedenstrom prey. We speculate that the condition (nutritional value), rather than the abundance of Sprat, has been important in changing the Guillemots feeding behaviour. The study indicates that the reason for the observed lower reproductive success was lower egg survival, most likely an effect of an increased predation pressure from Herring Gulls Larus argentatus.
