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Review of seabird demographic rates and density dependence

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This report presents individual species accounts for a selection of British seabirds, sea ducks, divers and grebes. Each account gathers the most up to date published estimates on the following demographic parameters: age-specific survival, age-specific productivity, age of recruitment, incidence of missed breeding, and natal and adult breeding dispersal. Particular attention has been given to regional variation in demographic rates, indicating the extent to which estimates may be applied to other less-well studied colonies. Where possible, the intrinsic and extrinsic factors that influence demographic rates are also detailed. The reported rates should enable population models that assess the impacts of offshore wind farms to be developed as reliably and realistically as possible. Where sufficient data could not be gathered using UK examples, data from colonies outside of the UK have been presented, or a proxy species has been identified. The evidence for density-dependent regulation of seabird demographic rates is also reviewed using examples from the UK, as well as non-UK studies on similar species.
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... . The matrices were structured by age and the dimensions matched the mean age of first reproduction for black-legged kittiwake, i.e., four years (Horswill & Robinson, 2015). We calculated the elasticity of each demographic rate using the statistical package "popbio" (v. ...
... Therefore, population-specific estimates of juvenile (i.e., from fledging to age 1 year) and immature (i.e., before the age of first breeding) survival rates are limited (Horswill & Robinson, 2015). Available estimates for black-legged kittiwakes breeding in France report rates of juvenile survival ( ) to be 75% of adult i J survival, immature rates of survival between age 1 and 2 years to be 87.5% of adult survival ( ), and birds i I to have survival rates comparable to adults from age 2 onwards (Cam, Cooch, & Monnat, 2005). ...
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Predicting how populations may respond to climate change and anthropogenic pressures requires detailed knowledge of demographic traits, such as survival and reproduction. However, the availability of these data varies greatly across space and taxa. Therefore, it is common practice to conduct population assessments by filling in missing values from surrogate species or other populations of the same species. However, using these independent surrogate values concurrently with observed data neglects the life‐history trade‐offs that connect the different aspects of a population's demography, thus introducing biases that could ultimately lead to erroneous management decisions. We use a Bayesian hierarchical approach to combine fragmented multi‐population data with established life‐history theory and reconstruct population‐specific demographic data across a substantial part of a species breeding range. We apply our analysis to a long‐lived colonial species, the black‐legged kittiwake Rissa tridactyla, that is classified as globally Vulnerable and is highly threatened by increasing anthropogenic pressures, such as offshore renewable energy development. We then use a projection analysis to examine how the reconstructed demographic parameters may improve population assessments, compared to models that combine observed data with independent surrogate values. Reconstructed demographic parameters can be utilised in a range of population modelling approaches. They can also be used as reference estimates to assess whether independent surrogate values are likely to over or underestimate missing demographic parameters. We show that surrogate values from independent sources are often used to fill in missing parameters that have large potential demographic impact, and that resulting biases can be driven in unpredictable directions thus precluding assessments from being consistently precautionary. Synthesis and applications: Our study dramatically increases the spatial coverage of population‐specific demographic data for black‐legged kittiwakes. The reconstructed demographic parameters presented can also be used immediately to reduce uncertainty in the consenting process for offshore wind development in the UK and Ireland. More broadly, we show that the reconstruction approach used here provides a new avenue for improving evidence‐based management and policy action for animal and plant populations with fragmented and error prone demographic data.
... Several reviews of appropriate PVA model structure and parameter specification for marine birds considering OWED have been conducted Freeman et al., 2014;Horswill and Robinson, 2015;Maclean et al., 2007;Potiek et al., 2022;Searle et al., 2020;Trinder and Furness, 2015). These reviews identified varying methods depending upon the focus of the study, life history characteristics of the focal species, and/or availability of data at focal colonies. ...
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Offshore wind energy development (OWED) is rapidly expanding globally and has the potential to contribute significantly to renewable energy portfolios. However, development of infrastructure in the marine environment presents risks to wildlife. Marine birds in particular have life history traits that amplify population impacts from displacement and collision with offshore wind infrastructure. Here, we present a broadly applicable framework to assess and mitigate the impacts of OWED on marine birds. We outline existing techniques to quantify impact via monitoring and modeling (e.g., collision risk models, population viability analysis), and present a robust mitigation framework to avoid, minimize, or compensate for OWED impacts. Our framework addresses impacts within the context of multiple stressors across multiple wind energy developments. We also present technological and methodological approaches that can improve impact estimation and mitigation. We highlight compensatory mitigation as a tool that can be incorporated into regulatory frameworks to mitigate impacts that cannot be avoided or minimized via siting decisions or alterations to OWED infrastructure or operation. Our framework is 2 intended as a globally-relevant approach for assessing and mitigating OWED impacts on marine birds that may be adapted to existing regulatory frameworks in regions with existing or planned OWED.
... In Bayesian statistics, prior distributions can be used to summarise our understanding of how the world works to obtain meaningful inference from small and fragmented datasets (Hobbs and Hooten 2015). Like many seabirds, kittiwakes are largely unobservable during the first years of life, and population-specific estimates of juvenile survival rates are limited (Horswill and Robinson 2015). Similar to other species of seabird (Horswill et al. 2014), previous studies on age-specific survival in kittiwakes report that probabilities are similar during the first two years following fledging and vary additively with time across age-classes (Link et al. 2002, Cam et al. 2005, Aubry et al. 2009, Desprez et al. 2011. ...
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The source–sink paradigm predicts that populations in poorer‐quality habitats (‘sinks') persist due to continued immigration from more‐productive areas (‘sources'). However, this categorisation of populations assumes that habitat quality is fixed through time. Globally, we are in an era of wide‐spread habitat degradation, and consequently there is a pressing need to examine dispersal dynamics in relation to local population change. We used an integrated population model to quantify immigration dynamics in a long‐lived colonial seabird, the black‐legged kittiwake Rissa tridactyla, that is classified as globally ‘Vulnerable'. We then used a transient life table response experiment to evaluate the contribution of temporal variation in vital rates, immigration rates and population structure to realised population growth. Finally, we used a simulation analysis to examine the importance of immigration to population dynamics. We show that the contribution of immigration changed as the population declined. This study demonstrates that immigration is unlikely to maintain vulnerable sink populations indefinitely, emphasising the need for temporal analyses of dispersal to identify shifts that may have dramatic consequences for population viability.
... As observed in other seabird species, we assumed that the survival probability of birds in their first year at sea was lower than for birds older than 1 year (Horswill & Robinson, 2015;VanderWerf & Young, 2016). We allowed probabilities of survival, return and detection on Gough Island, and breeding success, to vary from ...
Article
Invasive species are one of the greatest drivers of biodiversity loss worldwide, and the eradication of invasive species from islands is a highly efficient management strategy. Because eradication operations require large financial investments, uncertainty over the magnitude of impacts of both invasive species and their removal can impede the willingness of decision makers to invest in eradication. Such uncertainty is prevalent for long‐lived species that display an inherent lag between life stages affected by invasive species and those used for population status assessments. Albatrosses are amongst the longest‐living bird species and are threatened on land by invasive species and at sea by industrial fisheries. As in many seabird species, usually only a segment of the population (breeding adults) is used for status assessments, making it difficult to assess albatross population trends and the potential benefit of conservation action, such as the management of predatory invasive species. We used population monitoring and mark‐recapture data to estimate the past population trajectory of the critically endangered Tristan albatross Diomedea dabbenena by accounting for unobservable birds at sea in an integrated population model. We then projected the future population trajectory of Tristan albatrosses for scenarios with or without predation by invasive house mice Mus musculus on their main breeding site, Gough Island. The adult breeding population remained stable between 2004 and 2021, but breeding success was low (31%) and our model indicated that the total population (including unobservable immature birds) decreased from a median estimate of 9,795 to 7,752 birds. Eradicating invasive mice leading to a two‐fold increase in breeding success would result in a 1.8–7.6 times higher albatross population by 2050 (median estimate 10,352 individuals) than without this intervention. Low reproductive output for long‐lived species may lead to a cryptic population decrease, which can be obscured from readily available counts of breeding pairs by changes in the population structure. Mouse eradication is necessary to halt the ongoing population decrease of the Tristan albatross, even if this decrease is not yet apparent in the breeding population size. Low reproductive output for long‐lived species may lead to a cryptic population decrease, which can be obscured from readily available counts of breeding pairs by changes in the population structure. Mouse eradication is necessary to halt the ongoing population decrease of the Tristan albatross, even if this decrease is not yet apparent in the breeding population size.
... Like many seabirds, kittiwakes are largely unobservable during the first years of life. Therefore, colony-specific survival estimates for juveniles (i.e., during the first year post fledging ϕ j,t ) and immatures (i.e., from 1 to 2 years ϕ i,t ) are limited (Horswill & Robinson, 2015). Available estimates for black-legged kittiwakes breeding in France report fledgling survival rates to be 75% of adults, immature survival rates (i.e., from age 1 to 2 years) to be 87.5% of adults, and survival rates to be comparable to adults from age 2 onwards (Cam et al., 2005). ...
Article
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Population viability analyses (PVA) are now routinely used during the consenting process for offshore wind energy developments to assess potential impacts to vulnerable species, such as seabirds. These models are typically based on mean vital rates, such as survival and fecundity, with some level of environmental stochasticity (i.e., temporal variation). However, many species of seabird are experiencing population decline due to temporal (i.e., directional) trends in their vital rates. We assess the prevalence of temporal trends in rates of fecundity for a sentinel species of seabird, the black‐legged kittiwake Rissa tridactyla, and examine how accounting for these relationships affects the predictive accuracy of PVA, as well as the projected population response to an extrinsic threat. We found that temporal trends in kittiwake rates of fecundity are widespread, and that including these trends in PVA assessments dramatically influences the projected rate of population decline. We advocate that model validation become a prerequisite step in seabird PVA assessments to identify potential biases influencing the projected population response. We also argue that environmental factors driving current population dynamics need to be incorporated in PVA impact assessments as potential “worst‐case” scenarios. These findings have immediate application for improving and reducing uncertainty in impact assessments conducted as part of the consenting process for offshore wind energy developments.
... A number of seaduck species and populations are believed to be in decline, although specific drivers have yet to be identified in many cases IUCN, 2021;SDJV, 2007). Even the beststudied species, the common eider (Somateria mollissima) (Horswill & Robinson, 2015;Skarphedinsson, 1996) is classed by the IUCN as near threatened with an 'unknown' global population trend (BirdLife International, 2018). This is not due to a lack of scientific or popular interest: the common eider is a charismatic species with a large Holarctic distribution, across which it has come into direct contact with humans through hunting and eiderdown farming since at least the seventh century (Berglund, 2009;Goryashko, 2020;Waltho & Coulson, 2015). ...
Article
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This database collates vital rate estimates for the common eider (Somateria mollissima), providing a complete demographic parameterization for this slow life‐history species. Monitored across its circumpolar range, the common eider represents a data‐rich exemplar species for the less‐studied seaducks, many of which are under threat. The database contains estimates of the following vital rates: first- year survival; second- year survival; adult annual survival; first breeding (both age‐specific recruitment probability, and breeding propensity across potential recruitment ages); breeding propensity of established female breeders; clutch size; hatching success; and fledging success. These estimates are drawn from 134 studies, across the scientific and grey literature, including three previously inaccessible datasets on clutch size that were contributed in response to a call for data through the IUCN Species Survival Commission's Duck Specialist Group. Although clutch size has been much studied, the contributed datasets have enhanced coverage of studies reported in non‐English languages, which were otherwise only represented when cited in English‐language publications. Breeding propensity has been little studied, perhaps because adult females are often assumed to attempt breeding every year; we obtained a mean breeding propensity of 0.72. Our synthesis highlights the following gaps in data availability: juvenile and male survival; population change; and studies from Russia (at least accessible in English). The database is intended to serve population modellers and scientists involved in the policy and practice of seaduck conservation and management.
... Les résultats obtenus grâce au suivi à long terme mené sur les colonies d'océanites de l'archipel de Molène sont donc totalement inédits pour cette espèce. Classiquement, chez les oiseaux marins, la survie est plus faible pour les jeunes individus et augmente ensuite avec l'âge pour se stabiliser chez les adultes reproducteurs (Horswill & Robinson 2015). Ainsi par exemple, chez le fou de Bassan Morus bassanus, la survie est respectivement de 0,42 à 1 an, 0,83 à 2 ans, 0,89 à 3 ans, 0,90 à 4 ans et 0,92 ensuite chez les adultes (Wanless et al. 2006). ...
... There may be additional opportunities to analyse the relationship between body mass and survival in other regions of the UK for species identified as being particularly at risk from ORDs. Although the number of studies of survival of UK seabirds is limited (Horswill et al. 2015), some may include a proportion of individuals where body mass has been taken, so analyses similar to this may be possible. However, it is likely that all such studies will suffer from the same data deficiencies that we observed. ...
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Offshore renewable developments (ORDs) may negatively affect seabirds, in particular due to collisions with turbine blades, displacement to less favourable habitats and barrier effects to movement. Many so-called 'sub-lethal effects', whereby individuals birds are not killed instantaneously by an interaction with the wind farm, but behaviour is affected in the short term, may have knock on effects on energetic budgets and, in turn, demographic rates such as survival and productivity. A key potential process linking sub-lethal effects of ORDs and demography is the relationship between adult body condition at the end of the breeding season and survival probability the following winter. However, our understanding of this relationship is limited. Using long-term data collected on the Isle of May, Scotland, this report investigates the relationship between body mass during breeding and survival for 4 seabird species. For puffins, we found evidence for a strongly positive relationship between individual-specific body mass at the end of the breeding season and the probability of survival to the start of the next breeding season. In contrast, in kittiwakes, guillemots and razorbills, the estimated effect sizes were considerably smaller. In conclusion, using the best available UK data and employing advanced methods of statistical analysis, we found evidence for a positive relationship between end-of-breeding season body mass and the survival of puffins with less evidence of an effect in kittiwakes, guillemots and razorbills. We consider these estimates more suitable for use, especially in a UK context, than relationships estimated from other studies.
... This highlights the importance of obtaining accurate parameter values and associated variability across the region of interest for factors 1-3 relating to behaviour given their relative importance in calculating species SOSI scores. The results also partially allay concerns that the SOSI does not consider spatial and temporal variation in seabird demography, with variability observed in the maximum and mean clutch size, age at first breeding and adult survival rate (Horswill and Robinson 2015). The relatively low influence of demographic factors suggests that it may not be essential to account for this variation, or uncertainty in these parameter values for understudied populations, or species, and that data from surrogate species, expert opinion, or local ecological knowledge may be an appropriate alternative when data are lacking. ...
Chapter
In recent decades, political and commercial interest in the Arctic’s resources has increased dramatically. With the projected increase in shipping activity and hydrocarbon extraction, there is an increased risk to marine habitats and organisms. This comes with concomitant threats to the fragile Arctic environment especially from oil, whether from shipping accidents, pipeline leaks, or sub-surface well blowouts. Seabirds are among the most threatened group of birds, and the main threats to these species at-sea are commercial fishing and pollution. Seabirds are vulnerable to oil pollution, which can result in mass mortality events. Species are affected to a differing extent, therefore it is important to objectively predict which species are most at risk from oil spills and where. Assessing the vulnerability of seabirds to oil is achieved through establishing an index for the sensitivity of seabirds to oil – Oil Vulnerability Index (OVI). This incorporates spatial information on the distribution and density of birds as well as on species specific behaviours and other life history characteristics. This chapter focuses on the threat of oil to seabirds, especially in the Arctic, and how an OVI can be used to highlight which species are most at risk and where within the Arctic region.
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Note de synthèse décrivant la méthodologie de choix pour quantifier l'impact démographique des collisions sur les populations d'oiseaux. Une comparaison détaillée entre deux approches possibles (le PBR: Potential Biological Removal ; et les projections démographiques) est faite.
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Red-throated Loon (Gavia stellata) numbers in Alaska have fluctuated dramatically over the past 3 decades; however, the demographic processes contributing to these population dynamics are poorly understood. To examine spatial and temporal variation in productivity, we estimated breeding parameters at 5 sites in Alaska: at Cape Espenberg and the Copper River Delta we estimated nest survival, and at 3 sites within the Yukon-Kuskokwim Delta we estimated nest survival and productivity. Nest survival varied broadly among sites and years; annual estimates (lower, upper 95% confidence interval) ranged from 0.09 (0.03, 0.29) at Cape Espenberg in 2001 to 0.93 (0.76, 0.99) at the Copper River Delta in 2002. Annual variation among sites was not concordant, suggesting that site-scale factors had a strong influence on nest survival. Models of nest survival indicated that visits to monitor nests had a negative effect on nest daily survival probability, which if not accounted for biased nest survival strongly downward. The sensitivity of breeding Red-throated Loons to nest monitoring suggests other sources of disturbance that cause incubating birds to flush from their nests may also reduce nest survival. Nest daily survival probability at the Yukon-Kuskokwim Delta was negatively associated with an annual index of fox occurrence. Survival through the incubation and chick-rearing periods on the Yukon-Kuskokwim Delta ranged from 0.09 (0.001, 0.493) to 0.50 (0.04, 0.77). Daily survival probability during the chick-rearing period was lower for chicks that had a sibling in 2 of 3 years, consistent with the hypothesis that food availability was limited. Estimates of annual productivity on the Yukon-Kuskokwim Delta ranged from 0.17 to 1.0 chicks per pair. Productivity was not sufficient to maintain population stability in 2 of 3 years, indicating that nest depredation by foxes and poor foraging conditions during chick rearing can have important effects on productivity.
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Fishing boats in the North Sea and west of Britain may discharge 95 000 tonnes of offal and 135 000 tonnes of whitefish discards each year, enough to feed two million scavenging seabirds. Fulmars Fulmarus glacialis take most offal. Success rates in obtaining discards are gannet Sula bassana>great skua Stercorarius skua>great black-backed gull Larus marinus>lesser black-backed gull L. fuscus>herring gull L. argentatus>kittiwake Rissa tridactyla and fulmar. Gannets mainly exploit discards in spring, when they cause a reduced feeding success in, and partially displace, herring gulls from feeding at boats. Lesser black-backs show a greater tendency than herring gulls to feed at boats rather than at refuse tips. Numbers foraging at boats in the Clyde. W Scotland, in summer are large in relation to breeding numbers for lesser and great black-backed gulls. Discards are important for adult gulls of these species in summer. Discards can be an important part of herring gull chick diets but are less important for adults. Planned net-mesh changes to reduce discarding and a trend to use offal rather than discharge it may have pronounced effects on scavenging seabird populations. -from Authors
Article
Report on results of census projects in Scotland, Norway and the USA. Breeding success and adult and immature survival of puffins are usually high, but the last is difficult to determine as a high proportion of young breed away from their natal colony. Populations can increase rapidly, eg 19% per annum on the Isle of May, 1973-81. The calculated intrinsic rate over this period was only 16% which suggests that there was net immigration. Later, adult and immature survival declined and the calculated increase was 5% per annum. The population had by then stabilized and immature survival was probably lower than the single estimate suggested; immature survival and immigration have critical effects on population size. Conditions in the North Sea, possibly winter food, appear to have changed. This change may be widespread as the annual survival rates for adults on Skomer and the Isle of May were significantly correlated and the birds from these colonies winter in different areas. Little can be done to conserve most species of seabird except to manage fish stock sensibly and control pollution. -Authors