Graham E. Austin

Predicting the spatial distribution of buzzard Buteo buteo nesting areas using a Geographical Information System and remote sensing

Predictive models of animal distributions based on habitat can be used to assess the likely effects of changes in landuse on a species. In this study we developed a model of the distribution of buzzard nests in part of Argyll, Scotland. The model was tested on a further study site. Habitat was described in terms of vegetation cover, derived from satellite imagery, and topography, using a digital terrain model to classify altitude, slope, aspect and ruggedness. This data base was incorporated into a Geographical Infonnation System. Environmental data, in the form of areas and boundary lengths of vegetation types and landscape classifications, were extracted from the data base for circular areas of various radii from the centre of 500m grid cells covering each study area. We also included counts of buildings and lengths of roadways. Both logistic regression analysis and discriminant function analysis were used to produce classification models, which assigned each grid cell a probability that it contained a buzzard nesting area. The best predictive model was based on median altitude, total boundary length between all vegetation categories, the amount of moorland and the length of boundary between pre-thicket forestry and open ground. This model successfully reclassified 96.88% of grid cells in the areas from which it was developed and 82.35% in a test area. Previous studies have frequently predicted the distribution of species within the environment, but here we were able to predict the distribution of nesting areas within the distribution of a species.

The likely impact of sea level rise on waders (Charadrii) wintering on estuaries

Abstract Global climate change may affect the internationally important populations of waders (Charadrii) throughout their annual ranges and in a variety of ways. Within Britain, those waders that winter on estuaries are likely to be affected in two principal manners: increasingly mild winter weather already appears to have affected the distributions of the waders within Britain and rising sea level threatens to alter coastal habitats. Wader densities are largely dependent on the availability of their invertebrate prey, which, in turn depends on the nature of the estuarine sediments, itself a function of estuary morphology. Thus changes in estuary morphology, such as might occur with sea level rise, can affect wader density. Models have thus been developed that allow wader densities to be predicted from readily measured aspects of estuary morphology. The MONARCH project used case studies which employed a Geographical Information System, digital elevation models, coastline management plans and sea level rise predictions to simulate incremental increases in sea level for two estuaries. At each increment, values of morphological measurements required by the models were extracted and wader densities were modelled. In both case studies the densities of wader species favouring muddy sediments decreased under management scenarios that allowed land behind existing sea defences to be reclaimed by the sea. However, the models suggest that where changes in estuary morphology were sufficiently large to bring about a decrease in bird densities, generally as a result of increased estuary width leading to sandier sediments the associated increased area more than compensated for the assumed degradation of habitat such that larger numbers could be accommodated overall.

Numbers of wintering waterbirds in Great Britain and the Isle of Man (1994/1995–1998/1999): II. Coastal waders (Charadrii)

Abstract Great Britains wintering coastal wader populations have been estimated for the period 1994/1995–1998/1999 from data provided from two sources: the Wetland Bird Survey (WeBS) and the Non-estuarine Coastal Waterfowl Survey (UK-NEWS). New methodology for estimating the number of wintering waders is applied. It imputes (fills in) the value of missing counts before estimating the population size of each species as being the mean of the largest annual count made between November and March over the relevant 5-year period. This methodology has led to an 11% larger estimate of the number of waders present on Great Britains coasts than the traditional approach based on averaging just January counts over a 5-year period, and it suggests that Great Britains coastline supports ca. 2.1 million waders. Updated values are presented from which site evaluations based on 1% of the national population can be derived. Great Britain is of considerable international importance for waders. It holds >25 and >50% of the flyway populations of nine and four species of wader, respectively, but for the first time since the start of monitoring in the early 1970s, the historical increase in the number of predominantly coastal waders wintering in Great Britain is coming to an end. Seven of the 14 species that have shown population changes of >5% since the last set of 1987/1988–1991/1992 population estimates have declined in numbers. The possible causes of the fluctuations in wader populations, such as climate change and changing nutrient inputs to coastal waters are discussed. There is an urgent need to identify the causative factors leading to these declines, and to use the new population estimates to identify new sites that should be afforded legal protection, an action that should help Great Britain maintain its internationally important wader populations. The decrease in the updated population estimate of Eurasian oystercatcher, for example, has made it possible to determine that 19 rather than 17 sites in Great Britain are worthy of statutory protection on the basis of holding 1% or more of its national population.

Estimates and trends of waterbird numbers wintering in Ireland, 1994/95 to 2003/04

Capsule There has been a decline in the numbers of waterbirds wintering in Ireland between 1994/95 and 2003/04, including a 5% decline in wildfowl and an 11% decline in waders. Aims To provide estimates of numbers and trends in relative abundance of selected waterbird species wintering on the island of Ireland. Methods Waterbird counts were undertaken at key wetland sites in Ireland each winter (September to March) between 1994/95 and 2003/04. For each species, estimates were calculated for two five-season periods (1994/95–1998/99 and 1999/2000–03/04), while trends in relative abundance were analysed over the entire ten-season period. Counts were modelled using a multiplicative log-linear index model, with site, year and month factors. Results National estimates of overwintering numbers were produced for 42 species of waterbirds, and used to produce all-Ireland 1% thresholds (which are used to evaluate the importance of wetland sites). In winter, large proportions of several populations occur in Ireland, particularly Whooper Swan Cygnus cygnus, Greater White-fronted Goose (Greenland race) Anser albifrons flavirostris, Brent Goose (Canadian Light-bellied race) Branta bernicla hrota and Black-tailed Godwit Limosa limosa islandica. Of the 39 species for which trends were measured, 18 showed annual declines in excess of 2%, while ten species had increased. Numbers of the remaining 11 species were relatively stable. For many species, the trends measured appear to be continuations of longer-term changes since the 1970s. Conclusion These most recent estimates of waterbird numbers have been improved compared with those previously generated, due to improved levels of coverage and better analytical methods. This study highlights that there have been significant changes in the numbers of waterbirds wintering in Ireland over the past 30 years. The fact that many of these trends parallel wider flyway-scale population trajectories implies that large-scale drivers (e.g. climate change) may be responsible. However, many of the observed declines are likely to be a consequence of increased economic development which has led to direct habitat loss to industrial and residential development.

Surveying waterbirds away from major waterbodies: implications for waterbird population estimates in Great Britain

Capsule Population size estimates of widely dispersed waterbird species in Great Britain were improved using a stratified random sample of habitats in addition to standard counts of known wetlands. Aims To improve the estimation of national population sizes for species less well covered by the UK Wetland Bird Survey (WeBS) using a stratified random sampling approach. Methods Observers recorded habitat type and waterbird numbers within a stratified random sample of 1-km grid squares across Great Britain. For 20 species, population sizes were estimated using boot-strap techniques. These totals were added to WeBS Core Count and Non-Estuarine Coastal Waterbird Survey (UK-NEWS) data and the resulting Dispersed Waterbird Survey (DWS) estimate compared with published national population estimates. Results DWS estimates exceeded published national estimates by more than 50% for eight species but were lower for Pochard Aythya farina, Goldeneye Bucephala clangula and Moorhen Gallinula chloropus. Conclusions Our analyses suggest that the DWS provides a useful source of supplementary information for several dispersed species and demonstrates the value of a stratified random sampling approach for monitoring waterbird populations.

Population estimates of waders on the non- estuarine coasts of the UK and the Isle of Man during the winter of 1997-98

Capsule An updated estimate is presented and major declines in the internationally important populations of several species identified. Aims To provide population estimates of the waders overwintering on the UK and Isle of Mans non-estuarine coasts. Methods UK-NEWS was a repeat of the 1984–85 Winter Shorebird Count (WSC). The WSC results were reanalysed to allow direct comparison with the UK-NEWS results. The new population estimates are provided with bootstrapped confidence intervals. Results UK-NEWS covered 4959 km or 38% of the UKs non-estuarine coastline and recorded over 170 000 waders of 19 species. The new population estimates for the UKs non-estuarine wader species are as follows (values in parentheses are percentages of the East Atlantic Flyway population of each species): 70 790 Oystercatcher Haematopus ostralegus (7%), 24 110 Ringed Plover Charadrius hiaticula (33%), 28 670 Golden Plover Pluvialis apricaria (2%), 2175 Grey Plover Pluvialis squatarola (1%), 41 180 Lapwing Vanellus vanellus (1%), 7625 Knot Calidris canutus (2%), 13 660 Sanderling Calidris alba (11%), 17 220 Purple Sandpiper Calidris maritima (9%), 27 880 Dunlin Calidris alpina (2%), 3670 Bar-tailed Godwit Limosa lapponica (3%), 66 330 Curlew Numenius arquata (16%), 33 820 Redshank Tringa totanus (18%) and 39 560 Turnstone Arenaria interpres (42%). Similarly the Isle of Man held 887 Ringed Plover (1%), 8895 Curlew (2%) and 5220 individuals of the other species. Conclusion Eight species have increased and five have declined in the UK since the 1984–85 survey. We discuss the possible reasons for the declines of Ringed Plover (−15%), Sanderling (−20%), Purple Sandpiper (−21%), Bar-tailed Godwit (−44%) and Turnstone (−16%), species whose numbers on the UKs non-estuarine coasts are internationally important.

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.

An approach to the assessment of change in the numbers of Canada Geese Branta canadensis and Greylag Geese Anser anser in southern Britain

Capsule Population change in geese was assessed using an approach that requires a relatively small sampling effort. Aims During the 1999 breeding season a survey was carried out to determine if the numbers of introduced Canada and re-established Greylag Geese in southern Britain had changed since 1988–91 and whether any change had occurred in areas with previously high or low Canada Goose densities. Methods A randomized stratified sample of 246 tetrads from the 24 156 tetrads covered between 1988–91 in this area, as part of the New Atlas of Breeding Birds, were resurveyed. Eight habitat categories were used in the stratification and were based on 1-km-square summary data obtained from the CEH Land Cover Map of Great Britain (water cover and urbanization) and LANDCLASS stratification (upland/lowland). The five habitat categories with the highest densities of Canada Geese and the greatest variance in numbers were sampled. Results Between 1989 and 1999, the number of Canada Geese on land with over 5% water cover and on lowland with some water cover increased by on average 156%, an average rate of increase of 9.9% per annum. Southern Britain probably now holds a minimum of 82 000 Canada Geese. Between 1989 and 1999, the number of Greylag Geese on land with over 5% water cover and on lowland with some water cover increased by on average 214%, an average rate of increase of 12% per annum. Southern Britain probably now holds a minimum of 30 000 Greylag Geese. Conclusion Maximum densities of Canada Geese may have been reached in high-density habitats but their numbers are still increasing very rapidly. Greylag Geese are increasing even more rapidly.

Population size and differential population growth of introduced Greater Canada Geese Branta canadensis and re-established Greylag Geese Anser anser across habitats in Great Britain in the year 2000

Capsule Both populations are increasing at a similar rate. Aims During 2000, an extensive survey of introduced Greater Canada Geese and re-established Greylag Geese in Great Britain was undertaken in order to update population estimates last made between 1988 and 1991. Methods A randomized stratified sample of 1329 of the 61 510 tetrads (2 km × 2 km unit) in Great Britain was surveyed. The habitat categories, or strata, were based on the proportion of water cover, urbanization, and upland/lowland in each tetrad. Non-urbanized strata were further divided into northern and southern reporting areas. Results In 2000 there were an estimated 88 866 full-grown Greater Canada Geese and 24 522 full-grown Greylag Geese in Great Britain. Since the 1988–91 survey, Greater Canada Geese have increased by 166% and Greylag Geese by 170%, an average per annum rate of increase of 9.3% for Greater Canada Geese and 9.4% for Greylag Geese. The increase in Greater Canada Goose numbers since the 1988–91 survey has occurred mainly in habitats which had previously held low goose population densities, particularly the ‘no water’ lowland habitat. Although densities were still relatively low in this habitat (<0.5 geese per km2), because of its extent it supported 56% of the total Greater Canada Goose population in 2000. The greatest increase in re-established Greylag Goose numbers has arisen from an expansion into lowland habitat with some water cover. Conclusion There was no obvious decline in the 8.3% per annum Greater Canada Goose growth rate that caused the population to treble between 1976 and 1991. Greylag Goose numbers are increasing at a similar rate to those of the Greater Canada Goose.

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.