Niall H. K. Burton

TEST OF A BEHAVIOR-BASED INDIVIDUAL-BASED MODEL: RESPONSE OF SHOREBIRD MORTALITY TO HABITAT LOSS

In behavior-based individual-based models (IBMs), demographic functions are emergent properties of the model and are not built into the model structure itself, as is the case with the more widely used demography-based IBMs. Our behavior-based IBM represents the physiology and behavioral decision making of individual animals and, from that, predicts how many survive the winter nonbreeding season, an important component of fitness. This paper provides the first test of such a model by predicting the change in winter mortality of a charadriid shorebird following removal of intertidal feeding habitat, the main effect of which was to increase bird density. After adjusting one calibration parameter to the level required to replicate the observed mortality rate before habitat loss, the model predicted that mortality would increase by 3.65%, which compares well with the observed increase of 3.17%. The implication that mortality was density-dependent was confirmed by predicting mortality over a range of bird densities. Further simulations showed that the density dependence was due to an increase in both interference and depletion competition as bird density increased. Other simulations suggested that an additional area of mudflat, equivalent to only 10% of the area that had been lost, would be needed by way of mitigation to return mortality to its original level. Being situated at a high shore level with the flow of water in and out impeded by inlet pipes, the mitigating mudflat would be accessible to birds when all mudflats in the estuary were covered at high tide, thus providing the birds with extra feeding time and not just a small replacement mudflat. Apart from providing the first, and confidence-raising, test of a behavior-based IBM, the results suggest (1) that the chosen calibration procedure was effective; (2) that where no new fieldwork is required, and despite being parameter rich, a behavior-based IBM can be parameterized quickly (few weeks), and thus cheaply, because so many of the parameter values can be obtained from the literature and are embedded in the model; and (3) that behavior-based IBMs can be used to explore system behavior (e.g., the role of depletion competition and interference competition in density-dependent mortality).

Modelling flight heights of marine birds to more accurately assess collision risk with offshore wind turbines

Summary 1. The number of offshore wind farms is rapidly increasing as they are a critical part of many countries’ renewable energy strategies. Quantifying the likely impacts of these developments on wildlife is a fundamental part of the impact assessments required in many regions before permission for developments is granted. A key concern related to wind turbines is the risk of birds colliding with turbine blades. We present a novel method to generate species-specific flight height distributions which can be used to improve the assessment of collision risk by better reflecting the proportion of in-flight populations at risk of collision. 2. Data describing the flight heights of birds from surveys of 32 potential offshore wind farm development sites were combined to estimate continuous distributions for 25 marine bird species. Observations of flying birds assigned to discrete height categories were treated as observations from independent multinomial distributions with a shared underlying continuous distribution. This analysis enables calculation of the uncertainty around the estimates of the proportion of the in-flight population at risk and consideration of different turbine designs. 3. The mean r 2 for model fit across species was 0� 85, and for seven of the species, good independent model validation (80% of independent observations within 95% confidence intervals) provides some confidence for use of the results at alternative sites. 4. All species exhibited positively skewed flight height distributions. These results demonstrate that under the conditions in which the data were collected, raising hub height and using fewer, larger turbines are effective measures for reducing collision risk. 5. Synthesis and applications. The methods presented here for modelling continuous flight height distributions provide measures of uncertainty and enable comparison of collision risk between different turbine designs. This approach will improve the accuracy of impact assessments and provide estimates of uncertainty, allowing better evidence to inform decisionmaking.

Differences in the diurnal and nocturnal use of intertidal feeding grounds by Redshank Tringa totanus

Capsule Redshank used more sites and had larger ranges at night than during the day. Aims To determine whether there were differences in how wintering Redshank used intertidal feeding grounds during the day and night. Methods The movements of 38 Redshank caught and radiotagged at two neighbouring sites on the Severn Estuary were monitored during four different study periods between January 1997 and October 1999. Results Individuals used a greater number of sites at night than in the day (on average, two as opposed to one). Kernel home range analyses also indicated that individuals used larger core areas and home ranges at night. In addition, there was a significant difference between the sizes of ranges of birds caught at two neighbouring sites. One foraging site was almost entirely avoided during the day, probably due to disturbance from an adjacent heliport, but was used by the majority of individuals at night when the heliport was unused. This site was rich in invertebrates as a result of the high organic and nutrient input from a sewage outfall pipe. Redshank also used riverine mudflats less during the night, preferring more open mudflats – perhaps to avoid nocturnal predators. Conclusions Comparison with previous studies suggests that the importance of sites predominantly used at night and the total extent of the areas used by waders may be underestimated by studies that rely on daytime surveys alone. It is important, therefore, that information on nocturnal distributions should be available to inform decisions on site management and protection.

Birds of the Severn Estuary and Bristol Channel: Their current status and key environmental issues

The Severn Estuary and Bristol Channel encompass a number of designated sites supporting populations of waterbirds and seabirds that are of national or international importance, including the Severn Estuary and Burry Inlet Special Protection Areas (SPAs)/Ramsar Sites and Carmarthen Bay, the UKs first marine SPA. Here, we provide an overview of the present numbers and trends of the waterbirds and seabirds using these sites, updating previous reviews undertaken prior to these designations. We further provide a summary of the main issues that have affected the status of the areas bird populations. Declines in the numbers of waders on the Severn Estuary and the southwest over the last two decades have been linked to climate change. The Sea Empress oil-spill impacted both breeding seabirds and the wintering Common Scoters in Carmarthen Bay, though numbers of the latter recovered 3years after the spill. At the Burry Inlet, Oystercatcher numbers have fallen over the last 25years and considerable research has been undertaken into the conflict with cockle and mussel fisheries. A long-term study at Cardiff Bay, at the mouth of the Severn, revealed a significant impact on the survival of Redshanks following its impoundment and has helped to further understanding of responses of waterbirds to estuarine habitat loss. The potential impacts of the construction of a tidal power scheme on the Severn Estuary are also discussed.

A trial of three harness attachment methods and their suitability for long-term use on Lesser Black-backed Gulls and Great Skuas

Tracking devices are useful in studying the movement and behaviour of birds throughout the year. However, the effects of device attachment must be monitored for bird welfare and the scientific veracity of information gathered. We report on a trial of three different harness types (leg-loop, body and wing) for attaching GPS devices to Lesser Black-backed Gulls Larus fuscus and of a leg-loop harness on Great Skuas Stercorarius skua. This trial evaluated the functionality of the device whilst deployed, harness retention and the effects of each harness on the birds. The leg-loop harness prevented the devices from charging, due to feathers overlapping their solar panels, and individuals of both species shed this attachment during the first breeding season. For Lesser Black-backed Gull, devices functioned properly when attached using body and wing harnesses; foraging behaviour and territory attendance of birds were similar to the findings of other studies. Despite small sample sizes, annual adult survival rates for Lesser Black-backed Gull were similar to published estimates, suggesting harnesses had no deleterious effects. The wing harness has a smaller amount of skin contact than the body harness, and a non-constricting fit that better accommodates changes in body size. The wing harness was therefore considered the most appropriate for long-term studies.

Modelling the abundance and distribution of marine birds accounting for uncertain species identification

Summary Many emerging methods for ecological monitoring use passive monitoring techniques, which cannot always be used to identify the observed species with certainty. Digital aerial surveys of birds in marine areas are one such example of passive observation and they are increasingly being used to quantify the abundance and distribution of marine birds to inform impact assessments for proposed offshore wind developments. However, the uncertainty in species identification presents a major hurdle to determining the abundance and distribution of individual species. Using a novel analytical approach, we combined data from two surveys in the same area: aerial digital imagery that identified only 23% of individuals to species level and boat survey records that identified 95% of individuals to species level. The data sets were analysed to estimate the effects of environmental covariates on species density and to produce species-specific estimates of population size. For each digital aerial observation without certain species identification, randomized species assignments were generated using the observed species proportions from the boat surveys. For each species, we modelled several random realizations of species assignments and produced a density surface from the ensemble of models. The uncertainty from each stage of the process was propagated, so that final confidence limits accounted for all sources of uncertainty, including species identification. In the breeding season, several species had higher densities near colonies and this pattern was clearest for three auk species. Sandeel density was an important predictor of the density of several gull species. Synthesis and applications. This method shows it is possible to construct maps of species density in situations in which ecological observations cannot be identified to species level with certainty. The increasing use of passive detection methods is providing many more data sets with uncertain species identification and this method could be used with these data to produce species-specific abundance estimates. We discuss the advantages of this approach for estimating the abundance and distribution of birds in marine areas, particularly for quantifying the impacts of offshore renewable developments by making the estimates derived from the older digital surveys more comparable to the recently improved surveys.

Great skua (Stercorarius skua) movements at sea in relation to marine renewable energy developments

Marine renewable energy developments (MREDs) are an increasing feature of the marine environment. Owing to the relatively small number of existing developments and the early stage of their associated environmental monitoring programmes, the effects of MREDs on seabirds are not fully known. Our ability to fully predict potential effects is limited by a lack of knowledge regarding movements of seabirds at sea. We used GPS tracking to improve our understanding of the movements at sea of a protected seabird species breeding in Scotland, the great skua (Stercorarius skua), to better predict how this species may be affected by MREDs. We found that the overlap of great skuas with leased and proposed MREDs was low; particularly with offshore wind sites, which are predicted to present a greater risk to great skuas than wave or tidal-stream developments. Failed breeders overlapped with larger areas of MREDs than breeding birds but the overall overlap with core areas used remained low. Overlap with wave energy development sites was greater than for offshore wind and tidal-stream sites. Comparison of 2011 data with historical data indicates that distances travelled by great skuas have likely increased over recent decades. This suggests that basing marine spatial planning decisions on short-term tracking data could be less informative than longer-term data.

Indexing winter gull numbers in Great Britain using data from the 1953 to 2004 Winter Gull Roost Surveys

Capsule Winter Gull Roost Survey data spanning 50 years were used to generate population indices. Aims To evaluate how wintering numbers of five gull species have changed in Great Britain over the last five decades. Methods Generalized linear models were used to relate gull numbers to habitat, site and year factors, and so derive species‐specific indices for nine regions of Great Britain. Regional models considered data from different timescales depending on coverage. Results Patterns of change varied by species and region. All species showed increases in number over the period 1953 to 2004. In most regions, Black‐headed Gull Chroicocephalus ridibundus numbers have declined since peaks between 1973 and 1993; Common Gulls Larus canus have also declined recently in some regions. Lesser Black‐backed Gull L. fuscus numbers have increased dramatically since 1953, whereas numbers of Herring Gull L. argentatus showed large declines between 1963 and 1983. Great Black‐backed Gull L. marinus numbers have increased in the west and the Midlands, but recently declined in eastern regions. Conclusions Numbers of wintering gulls in Great Britain have shown rapid changes over the last five decades, reflecting changes in the sizes of breeding populations. These changes are likely to be associated with changes in human activities and resource availability.

Improved estimates of population trends of Great Cormorants Phalacrocorax carbo in England and Wales for effective management of a protected species at the centre of a human–wildlife conflict

Capsule A new method of estimating winter Great Cormorant population trends was developed to improve monitoring. Aims To develop methods of estimating Cormorant population trends with confidence intervals by combining data from different monitoring schemes. Methods Estimates of inland and coastal winter Cormorant populations were made for England and Wales from 1988 to 2010. Annual counts from the Wetland Bird Survey were used, supplemented with Dispersed Waterbird Survey data for inland populations, and Non-Estuarine Coastal Waterbird Survey data for coastal populations. Bootstrapping was undertaken to produce confidence intervals. Results The winter Cormorant population in England and Wales increased by about 59% between 1988 and 2010. The annual trend of the inland population became less positive from 2004 onwards, the year in which numbers controlled under licence greatly increased. Conclusions The improved precision of the new estimates provides a sound basis on which to assess potential population-level effects of licensed control of Cormorants. Although there was an indication that recent declines in the inland population were concurrent with increased control intensity, this can only be considered weak evidence, and such effects may be better considered through intensive research on Cormorant site use and dispersal in relation to control activities.

The importance of the United Kingdom for wintering gulls: population estimates and conservation requirements

Capsule The UK supported over 3.8 million wintering gulls in 2003/04–2005/06. Aims To provide new winter population estimates for Great Britain, its constituent countries, Northern Ireland, Channel Islands and Isle of Man, for five species of gull. Methods Observers undertook counts of gulls at roosts across three winters. Population estimates were produced by combining counts from key inland and coastal sites and estimates derived from stratified random sampling of inland tetrads and coastal stretches. Results Over 3.8 million gulls were estimated to winter in the UK and its near-shore coastal waters, a total that, due to more comprehensive methods, adds appreciably to previous estimates. Results inform conservation listings and required site-based conservation measures. Twenty sites held internationally important numbers of individual species and 37 internationally important assemblages and provisionally could qualify as Special Protection Areas for gulls alone. Forty-nine sites held nationally important numbers of particular species and provisionally could be notified as Sites/Areas of Special Scientific Interest solely for their importance for gulls. Conclusions Given the importance of the UK for wintering gulls and the declining status of some species, there is a clear requirement to consider measures and information needs that would provide for their conservation.