Mark A. Eaton

The generation and use of bird population indicators in Europe

Global and regional targets to reduce the rate of biodiversity loss bring with them the need to measure the state of nature and how it is changing. A number of different biodiversity indicators have been developed in response and here we consider bird population indicators in Europe. Birds are often used as surrogates for other elements of biodiversity because they are so well known and well studied, and not for their unique intrinsic value as environmental indicators. Yet, in certain situations and at particular scales, trends in bird populations correlate with those of other taxa making them a valuable biodiversity indicator with appropriate caveats. In this paper, we look at two case studies, in the UK and Europe as a whole, where headline bird indicators, that is, summary statistics based on bird population trends, have been developed and used to inform and assist policy makers. Wild bird indicators have been adopted by many European countries and by the European Union as indicators of biodiversity and of sustainable development. In the discussion, we review the strengths and weaknesses of using bird populations in this way, and look forward to how this work might be developed and expanded.

Status of the Hen Harrier Circus cyaneus in the UK and Isle of Man in 2004, and a comparison with the 1988/89 and 1998 surveys

Capsule The population of breeding Hen Harriers in the UK and Isle of Man increased between 1998 and 2004, although country and regional trends differed. Aims To estimate the size of the UK and Isle of Man Hen Harrier breeding population in 2004, and to compare this with previous estimates made in 1988/89 and 1998. Methods Surveys were carried out in core and a stratified random sample of 10-km squares throughout the known range, using the same methods as in the 1988/89 and 1998 national surveys. Results There were an estimated 806 territorial pairs in the UK and Isle of Man in 2004, a significant 41% increase from the 1998 estimate of 570 pairs. Increases were found throughout, with the exception of south and east Scotland and England, where numbers decreased. Scotland held 79% of the UK and Isle of Man breeding population in 2004, and 10% of Scottish pairs were associated with non-moorland habitats, such as mature conifer plantations and scrub/brash. Conclusions There was a substantial increase in the breeding population in most regions of the UK and Isle of Man between 1998 and 2004, possibly aided by increased use of non-moorland habitats. However, populations declined in upland areas of southern and eastern Scotland and northern England. Continuing illegal persecution arising from perceived conflicts between breeding Hen Harriers and driven grouse shooting may be a major cause of these regional declines.

Abundance of male Black Grouse Tetrao tetrix in Britain in 2005, and change since 1995-96

Capsule There was a non-significant decline in the number of displaying males in Britain between 1995–96 and 2005, with a significant decline in Scotland. Aims To estimate the number of displaying male Black Grouse in Britain in 2005, and to compare this with the 1995–96 estimate. Methods Surveys were carried out in a stratified sample of 1-km (Wales) and 5-km (Scotland and England) squares throughout the known range, using similar methods to the 1995–96 survey. Results There were an estimated 5078 displaying males in Britain in 2005 (95% CI 3920–6156). This estimate is 22% less than the 1995–96 estimate of 6506, although these estimates are not significantly different. In Scotland, numbers fell by 29% overall, comprising large and significant declines of 49% and 69% in southwest and southeast Scotland, respectively, but small and non-significant declines in north (16%) and northeast Scotland (9%). In England, there was a non-significant decline of 11%, while in Wales numbers rose by 39%. Where numbers have declined there has been a decrease in the number, but not the size, of display groups. Display sites in Britain were at higher altitudes (median 400 m) in 2005 than in 1995–96 (median 340 m). Conclusion Although Black Grouse numbers in Wales increased, this survey provides evidence of a large decline in southern Scotland. The causes of this decline are not fully understood, and further research is urgently required to reveal the underlying mechanisms and implement appropriate conservation measures.

Developing and enhancing biodiversity monitoring programmes: a collaborative assessment of priorities

Summary Biodiversity is changing at unprecedented rates, and it is increasingly important that these changes are quantified through monitoring programmes. Previous recommendations for developing or enhancing these programmes focus either on the end goals, that is the intended use of the data, or on how these goals are achieved, for example through volunteer involvement in citizen science, but not both. These recommendations are rarely prioritized. We used a collaborative approach, involving 52 experts in biodiversity monitoring in the UK, to develop a list of attributes of relevance to any biodiversity monitoring programme and to order these attributes by their priority. We also ranked the attributes according to their importance in monitoring biodiversity in the UK. Experts involved included data users, funders, programme organizers and participants in data collection. They covered expertise in a wide range of taxa. We developed a final list of 25 attributes of biodiversity monitoring schemes, ordered from the most elemental (those essential for monitoring schemes; e.g. articulate the objectives and gain sufficient participants) to the most aspirational (e.g. electronic data capture in the field, reporting change annually). This ordered list is a practical framework which can be used to support the development of monitoring programmes. Peoples ranking of attributes revealed a difference between those who considered attributes with benefits to end users to be most important (e.g. people from governmental organizations) and those who considered attributes with greatest benefit to participants to be most important (e.g. people involved with volunteer biological recording schemes). This reveals a distinction between focussing on aims and the pragmatism in achieving those aims. Synthesis and applications. The ordered list of attributes developed in this study will assist in prioritizing resources to develop biodiversity monitoring programmes (including citizen science). The potential conflict between end users of data and participants in data collection that we discovered should be addressed by involving the diversity of stakeholders at all stages of programme development. This will maximize the chance of successfully achieving the goals of biodiversity monitoring programmes.

The status of breeding Woodlarks Lullula arborea in Britain in 2006

Capsule There have been marked increases (88%) in the breeding population and breeding range (46%) of Woodlarks in Britain between 1997 and 2006. Aims To provide an accurate assessment of the population and distribution of Woodlarks in Britain and how these have changed since a survey conducted in 1997. Methods Survey coverage included ‘core’ 1 km squares (known occupancy in 1997) and a stratified random sample, based on suitable habitat and soil type. Results A population estimate of 3064 territories was obtained, giving an increase of 88% since 1997, while the range of occupied 10 km squares had increased by 46%. The majority of territories were associated with two main habitat types; heathland (66.7%) and forestry plantation (32.4%), and farmland in the southwest (13.4%). Sandy soils held the majority of territories (80.3%). Conclusion In the UK, the Woodlark is a species of high to moderate conservation concern subject to a national Biodiversity Action Plan (BAP). This survey demonstrated that the population has increased to meet the BAP targets set in 1996 for population size and range expansions in England, and is on schedule to meet targets in Wales. The species has responded to conservation restoration projects and is highly dependent on forest management.

Factors constraining the distribution of Golden Eagles Aquila chrysaetos in Scotland: capsule Between 1992 and 2003 persecution appeared to be the main influential factor.

Capsule Between 1992 and 2003 persecution appeared to be the main influential factor. Aims To utilize temporal changes in the distribution and occupation of Golden Eagle territories in Scotland between the 1992 and 2003 national censuses to assess potential causes of regional and national population trends, by examining spatial associations with a number of potential constraints on the population. Methods The distribution of occupied and vacant territories in the 1992 and 2003 censuses were entered as layers in a Geographical Information System (GIS), along with boundaries of biogeographical regions (Natural Heritage Zones) for regional analyses. Additional GIS layers were created for potential factors that may constrain the eagle population: the distribution and abundance of persecution incidents, new commercial conifer forests, popular mountains for hillwalkers (as surrogates for recreational activity), and the density of sheep and Red Deer (as surrogates for carrion abundance), drawn from comparable time periods to the national eagle censuses. Analyses then looked for spatial associations between eagle territory status and those constraint factors that may have influenced change in territory status. Results We found little evidence to suggest that recreational disturbance was influential on the occupation of Golden Eagle territories, although some local effects may have occurred and further analyses are warranted. We could find evidence of only a limited number of territories having being abandoned recently due to the planting of commercial conifer forests. We also rejected the hypothesis that changes in territory occupation between national Golden Eagle censuses were influenced by change in carrion abundance. By contrast, results were consistent with the hypothesis that persecution was influential in the observed change in territory occupation between censuses, so that occupied eagle territories tended to decline where persecution was probably still influential and tended to increase where persecution had probably declined. Conclusion In accordance with earlier predictions based on models of the demographic influence of persecution, in the central and eastern Highlands where grouse moor management predominates, the eagle population continued to decline to levels where increasingly large areas of suitable habitat are unoccupied by breeding pairs.

Agricultural Management and Climatic Change Are the Major Drivers of Biodiversity Change in the UK.

Action to reduce anthropogenic impact on the environment and species within it will be most effective when targeted towards activities that have the greatest impact on biodiversity. To do this effectively we need to better understand the relative importance of different activities and how they drive changes in species’ populations. Here, we present a novel, flexible framework that reviews evidence for the relative importance of these drivers of change and uses it to explain recent alterations in species’ populations. We review drivers of change across four hundred species sampled from a broad range of taxonomic groups in the UK. We found that species’ population change (~1970–2012) has been most strongly impacted by intensive management of agricultural land and by climatic change. The impact of the former was primarily deleterious, whereas the impact of climatic change to date has been more mixed. Findings were similar across the three major taxonomic groups assessed (insects, vascular plants and vertebrates). In general, the way a habitat was managed had a greater impact than changes in its extent, which accords with the relatively small changes in the areas occupied by different habitats during our study period, compared to substantial changes in habitat management. Of the drivers classified as conservation measures, low-intensity management of agricultural land and habitat creation had the greatest impact. Our framework could be used to assess the relative importance of drivers at a range of scales to better inform our policy and management decisions. Furthermore, by scoring the quality of evidence, this framework helps us identify research gaps and needs.

Status of Capercaillie Tetrao urogallus in Scotland during winter 2003/04

Capsule The population estimate was 1980 individuals (95% confidence limits 1284–2758). Aim To produce a new national population estimate with greater precision than the previous survey, but retaining comparability. Methods A total of 643, 2-km-long transects were walked at sites throughout the recently occupied range. The survey intensity was high in a ‘primary’ stratum of woodland where Capercaillie have been recorded since 2000, and lower in a ‘secondary’ stratum where Capercaillie have been recorded prior to 2000 only. DISTANCE analysis software was used to calculate densities in the two strata and extrapolate to a total population estimate. Results The population estimate was 1980 individuals (95% confidence limits 1284–2758). Although this value is 84% greater than that from the previous survey in 1998/99 (1073 individuals), it lies within the confidence limits of that estimate (549–2041). A randomization test confirmed that the apparent increase since 1998/99 was not statistically significant. The range of sightings recorded in the survey, and the frequency of Capercaillie sightings in four regions, suggests that the majority of the population is concentrated in Badenoch and Strathspey, with few birds in the south of the range. Conclusion The revision to the survey design since the 1998/99 survey, along with an increase in survey effort, was successful in producing a more precise population estimate than in previous surveys. However, the imprecision in survey estimates still hampers the power to detect changes in the size of the population. A number of alternative sources of Capercaillie data suggest that there may have been a recent increase in the core areas for Capercaillie, most noticeably in Strathspey.

Status of Golden EagleAquila chrysaetosin Britain in 2003

Capsule The third complete survey of Golden Eagles in Britain found 442 pairs. Aim To investigate the population size, distribution and breeding success of Golden Eagles in Britain, for comparison with similar surveys in 1982–83 and 1992. Methods All known home-ranges were surveyed between January and August 2003, to record Golden Eagle presence, breeding attempts and productivity using a three-visit methodology. The first visits were made in January–March to look for the presence of eagles, the second in April–June to detect whether a breeding attempt was taking place and the third in July–August to establish breeding success. Results In total, 442 pairs were located, a slight increase on the numbers in 1982–83 and 1992. There was considerable variation in population trends at a regional level, with decreases since 1992 in the eastern and south-central Highlands but an increase in the Hebrides. The mean productivity in 2003 was 0.36 fledged birds/pair. There was significant variation in breeding success between regions with, as in previous surveys, productivity being highest in the eastern Highlands. Conclusion The British Golden Eagle population remains stable. There remain concerns regarding the future of this population, particularly due to the threat posed by illegal persecution, and these results provide some supporting evidence for concerns raised by previous analyses. Persecution related to grouse moor management could be depressing the population in the eastern Highlands, preventing expansion into suitable habitat still unoccupied, and may be reducing the pool of non-breeding adult ‘floaters’ which act as a buffer against adverse population impacts. However, the survey did detect increases in the Hebridean islands since 1992, which may be because of a reduction in persecution.

The status of the Hen Harrier, Circus cyaneus, in the UK and Isle of Man in 2010

Capsule The fourth national survey of Hen Harrier showed that the population in the UK and the Isle of Man declined significantly between 2004 and 2010. Aim To estimate the size of the breeding Hen Harrier population (with associated 95% confidence intervals) in the UK and Isle of Man, constituent countries and Scottish regions, in 2010 and calculate population change since previous surveys in 1998 and 2004. Methods Complete surveys were made of 10-km squares likely to be occupied by breeding Hen Harriers in England, Wales, Northern Ireland and the Isle of Man, using standard methods developed for previous national surveys. In Scotland, a ‘census’ area was non-randomly selected for survey by volunteers, and randomly selected squares were surveyed in two strata covering the rest of the known range. Results The UK and Isle of Man Hen Harrier population was estimated at 662 territorial pairs (95% confidence interval (CI): 576–770), a significant decline of 18% since 2004. Scotland holds the bulk (76%) of the population (505 territorial pairs; 95% CI: 417–612), with smaller numbers in Northern Ireland (59 pairs), Wales (57 pairs), the Isle of Man (29 pairs) and England (12 pairs). Declines of 49% and 20% were observed in the Isle of Man and in Scotland, respectively, whereas the Welsh population increased by 33%. A significant decrease was recorded in numbers of pairs using young and mature plantation forest in Scotland. Conclusion The breeding population of Hen Harriers in the UK and Isle of Man declined between 2004 and 2010. Notable decreases in Scotland and the Isle of Man may be related to habitat change and illegal persecution. Illegal persecution continues to limit the population size of harriers in England to very low levels.