Wild bird populations in England, 1970-2015
Wild bird populations in England, 1970-2015
Revised 29th June 2017
Enquiries to Department for Environment, Food and Rural Affairs Nobel House, 17 Smith Square, London, SW1P 3JR Public enquiries: 0208 225 7921 or Press enquiries: 0208 225 7317 Public enquiries & user feedback: [email protected]
Contents Executive summary ............................................................................................................. 1 Why monitor bird populations? ............................................................................................ 2 Understanding the bird population indices ........................................................................... 2 Assessing trends ................................................................................................................. 3 1. Native breeding wild bird populations in England ............................................................ 5 2. Breeding farmland bird populations in England ............................................................... 8 3. Breeding woodland bird populations in England ............................................................ 12 4. Breeding water and wetland bird populations in England .............................................. 16 5. Breeding seabird populations in England....................................................................... 22 6. Wintering waterbird populations in England ................................................................... 25 Main notes: methodological detail, limitations of the indicators and further information ..... 28 Annex A: Trends in bird species, by habitat group, in England .......................................... 30
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Why monitor bird populations? Bird populations have long been considered to provide a good indication of the broad state of wildlife in England. This is because they occupy a wide range of habitats and respond to environmental pressures that also operate on other groups of wildlife. In addition, there are considerable long-term data on trends in bird populations, allowing for comparison between short-term and long-term. Because they are a well-studied taxonomic group, drivers of change for birds are better understood than for other species groups, which enables better interpretation of any observed changes. Birds also have huge cultural importance and are highly valued as a part of England’s natural environment by the general public. However, the bird indicators presented in this publication are not intended, in isolation, as indicators of the health of the natural environment more widely. It is not possible to determine changes in the actual number of birds for each species in England each year, it is possible to estimate the relative change, from counts on sample plots surveyed as part of a range of national monitoring schemes1. Trends in bird populations are used by policy makers, government agencies and nongovernmental organisations as part of the evidence base to assess the effects of environmental management, such as agricultural practices, on bird populations. The trends are also used to assess the effectiveness of environmental interventions intended to address declines, such as agri-environment schemes targeted at farmland birds.
Understanding the bird population indices Individual bird species population trends, based on expert surveys, are calculated as an index. This relates the population in a given year to a ‘baseline’ – the first year that data are available – which is given a value of 100. Thereafter, the index is expressing the population as a percentage of this ‘baseline’. This annual Defra National Statistics Release presents data trends up to 2015 in populations of common birds (species with a population of at least 300 breeding pairs) that are native to, and breed in, England, with trends overall and for four main habitat groups (see Annex A for a list of birds in each group). The release also presents trends for wintering waterbirds, some of which also breed in England. The charts presented combine individual species indices2 into a single indicator to provide an overall trend for each group mentioned above. The indices are considered to give
1
See ‘Main notes’ at the end for more details of the surveys sources used. th Using a geometric mean - an average calculated by multiplying a set of index values and taking the n root, where n is the number of index values. More information can be found in Introduction to the Wild Birds Population Indicator. 2
2
reliable medium to long-term trends but strong reliance should not be attached to shortterm changes from year to year.
Assessing trends Two trends are referred to in the text: the unsmoothed indices show year-to-year fluctuation in populations, reflecting the observed changes in the survey results, and smoothed trends3, which are used to formally assess the statistical significance of change over time. Smoothed trends4 are used for both long and short-term assessments as they reduce the short-term peaks and troughs resulting from, for example, year to year weather and sampling variations. The most recent year of data, i.e. 2015 in this update, is likely to change due to the smoothing process following the inclusion of 2016 data in next year’s update. As a result it is not appropriate to make assessments based on this figure. Where results from the smoothed indices are quoted, this is clearly indicated. These trends are based on estimates from surveys. Smoothed trends are presented with 95% confidence intervals (CI), which are a measure of the precision of these survey estimates: a 95% CI means we are 95% confident that the true value of an indicator in a given year falls within the confidence interval around it. The size of confidence intervals varies among habitat indicators because the width of the confidence interval is influenced by the number of species in each indicator and the precision of the individual species trends that make up the indicator. The precision of trends varies due to differences in sample size. Throughout this release, assessment periods are referred to as:
‘Long-term’ – an assessment of change since the earliest date for which data are available; this varies among habitat indicators and among individual species. ‘Short-term’ – an assessment of change over the latest five years (2009-2014).
Annex A shows long-term and short-term assessments for each individual bird species.
3
There are currently no smoothed trends available for seabirds. See analytical methods on BTO website (www.bto.org/birdtrends2011/methodology.htm) Fewster et al. 2000. Ecology 81: 1970-84. 4
3
Alongside the overall index, the percentage of species within each indicator that have increased or decreased in the long-term and in the short-term is also shown. This is based on the rate of annual change over the long or short-term, categorised by how much the population would change if that annual change continued for 25 years. The bar chart illustrates the percentage of species falling into each category: Strong increase: population increase above 50% increase Weak increase: above 33% but less than 50% increase No change: between a 25% decrease and a 33% increase Weak decline: less than 50% but greater than 25% decrease Strong decline: population decrease of 50% These thresholds are asymmetrical to represent symmetrical proportional change in an index. These thresholds are used in the formal, Government endorsed, Birds of Conservation Concern5 status assessment for birds in the UK. The bird population indices have been compiled in conjunction with the Royal Society for the Protection of Birds (RSPB), the British Trust for Ornithology (BTO) and the Joint Nature Conservation Committee (JNCC).
5
See the BTO website (http://www.bto.org/volunteer-surveys/birdtrack/bird-recording/birds-conservationconcern)
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Species breakdown The all-species index comprises of 118 species of birds, of all widespread species, with populations of at least 300 breeding pairs for which we have sufficient data. Species trends within this index vary widely, from species increasing several-fold (e.g. blackcap, buzzard, cetti’s warbler, great spotted woodpecker, and collared dove) to those having declined to less than a tenth of 1970 levels (turtle dove, tree sparrow, willow tit and grey partridge). The main patterns and drivers of change are considered by looking at the indices of species grouped by habitat in Figure 1b and the following chapters. Figure 1b: Populations of wild birds in England by habitat, 1970-2015
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2. Breeding farmland bird populations in England Farmland refers to the large proportion of England which is devoted to agriculture and consists of fields and grasslands habitat. Farmland also provides semi-natural habitats such as hedgerows and field margins that provide food and shelter to birds. In 2015 the England farmland bird index was less than half its 1970 value. The majority of this decline occurred between the late seventies and early eighties largely due to the impact of rapid changes in farmland management during this period. More recently, since 1990, the decline has slowed; the smoothed index decreased by 7% between 2009 and 2014. Figure 2: Breeding farmland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
Long-term Since 1970, 21% of species in the indicator showed a weak increase, 26% showed no change and 53% showed either a weak or a strong decline. Short-term Over the short-term period between 2009 and 2014, 42% of species in the indicator showed an increase, 26% showed no change and 32% showed a decline.
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Factors affecting farmland bird populations The large declines in the abundance of some farmland birds have many known and potential causes. Many of the declines have been caused by land management changes and the intensification of farming that took place since the 1950s and 60s, such as the loss of mixed farming, a move from spring to autumn sowing of arable crops, change in grassland management (e.g. a switch from hay to silage production), increased pesticide and fertiliser use, and the removal of non-cropped features such as hedgerows. The rate of these changes, which resulted in the loss of suitable nesting and suitable feeding habitats, and a reduction in available food, was greatest during the late 1970s and early 1980s, the period during which many farmland bird populations declined most rapidly. Some farming practices still have negative impacts on bird populations, but most farmers can and do take positive steps to conserve birds on their land. In particular, a number of incentive schemes encourage improved environmental stewardship in farming, with some measures specifically designed to help stabilise and recover farmland bird populations. These include the provision of over-wintered stubbles and planted wild bird crop covers to provide seed in the winter, uncropped margins on arable fields and sympathetic management of hedgerows. Changes in numbers experienced by some species may, to a lesser extent, be further driven by other pressures. For example, there is evidence of an adverse impact for some species from disease. Species breakdown The farmland bird index comprises 19 species of bird. The long-term decline of farmland birds in England has been driven mainly by the decline of those species that are restricted to, or highly dependent on, farmland habitats (the ‘specialists’). Between 1970 and 2015, the farmland specialists index declined by 71% while farmland generalists increased by 3%. Both smoothed trends showed declines, of 72% and 4% respectively (figure 2a). Figure 2a: Breeding farmland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trends (dashed lines) and smoothed trends (solid lines).
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3. Breeding woodland bird populations in England Woodland trees provide nesting for birds as well as foraging opportunities and cover from predators. In 2015 the breeding woodland bird indicator for England was 21% lower than in 1970. The greatest decline occurred between the early eighties and the early nineties, since 1996 the index has been more stable. Over the past 10 years the woodland bird index has showed no significant change despite some yearly fluctuations. Figure 3: Breeding woodland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
Long-term Since 1970, 26% of woodland species have increased in number, 45% showed no change and 29% declined, the majority of these showed a strong decline. Short-term Over the short-term period between 2009 and 2014, 32% of species showed an increase, 29% showed no change and 38% showed a decline. In contrast to over the long-term, the majority of declining species showed weak rather than strong decline. A number of species showed a long-term trend of no change, but a weak decline in the short-term such as the chaffinch, garden warbler and the long tailed tit. A few species showed strong decline in the long-term but weak decline in the short-term: marsh tit, willow tit. In contrast, lesser redpoll showed strong increase in the short-term, after a long-term trend of a strong decline. 12
Factors affecting woodland birds The declines in woodland birds have several known and potential causes, such as a lack of woodland management and increased deer browsing pressure, both of which result in a reduced diversity of woodland structure and, reduced availability of suitable nesting and foraging habitats. In addition, several declining woodland birds are long-distance migrants, and a decline in the extent or quality of habitats used outside the breeding season may be one factor affecting these species outside of England.
Species breakdown The woodland bird index comprises 34 species of bird. The relatively stable trend for all woodland birds from the late -1990s masks different underlying trends for: specialist species, which are highly dependent on woodland habitats; and generalist species, which are found in a wide range of habitats, including woodland. The long-term decline of woodland birds in England has been mostly driven by the decline of specialist woodland birds. Between 1970 and 2015, the index for woodland specialists declined by 34% while the woodland generalist index showed little change. The smoothed trend shows a decline of 36% for specialists and no significant change for generalists (figure 3a). Figure 3a: Breeding woodland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trends (dashed lines) and smoothed trends (solid lines).
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4. Breeding water and wetland bird populations in England Water and wetlands include rivers, lakes, ponds, reedbeds, grazing marshes and lowland raised bogs, all providing important habitats for birds. Water and wetland bird numbers have remained fairly stable for most of the period since data collection started in 1975. In 2015 the water and wetland bird index exceeded it’s 1975 level by 8%. Numbers rose slightly in the early 2000s but more recently the smoothed index showed a significant decline of 5% between 2009 and 2014. Figure 4: Breeding water and wetland birds in England, 1975-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
Long-term For the 25 species for which a long-term trend can be calculated, 32% of species showed an increase, 40% showed no change and 28% showed a decline, the majority of species exhibiting a change showed a weak rather than a strong change. For little egret, data collection started in 2004 and therefore a long-term trend could not be calculated (for more information on the time series used for different species long-term trends, see Annex A).
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Short-term Over the short-term period between 2009 and 2014, 23% of species showed an increase, 23% showed no change and 54% showed a decline. This change in trend was mostly caused by a large number of species moving down one category (e.g. weak increase to no change) rather than large changes in the species trends over time. Factors affecting water and wetland bird populations The historical declines in breeding waders, resulted from land management changes such as drainage, the intensification of grassland management and the conversion of coastal and floodplain grazing marshes to arable land. Where populations persist in small fragments of high quality habitat, their nests and young are vulnerable to predation, which is currently thought to be limiting the recovery of several species of breeding wader. Species breakdown The 26 species of bird included in the water and wetland bird index can be split into four sub-habitat indicators. Although the all species index shows a relatively stable trend this masks underlying differences between sub-habitat indicators (figure 4a). When interpreting these trends it should be borne in mind that each sub-habitat trend is derived from relatively few species trends. Figure 4a: Breeding water and wetland birds in England, 1975-2015
Note: i) figures in brackets show the number of species, ii) graph shows unsmoothed trends (dashed lines) and smoothed trends (solid lines),
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5. Breeding seabird populations in England The English coast consists of a wide variety of habitats such as sea cliffs, sand dunes, shingle ridges and machair and intertidal areas. In 2015, the breeding seabird index in England was 22% higher than in 1986, the highest level ever recorded. Despite fluctuations the indicator has increased steadily since the late nineties driven mainly by subsurface piscivore species. Figure 5: Breeding seabirds in England, 1986-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (solid line) - no smoothed trend is available for seabirds as individual species population trends are based on census data.
Long-term Between 1986 and 2014, 27% of 11 seabird species showed an increase, 45% showed no change and 27% showed either a weak or a strong decline. Short-term Over the short-term period between 2009 and 2014, 45% of species showed an increase, 18% showed no change and 36% showed a decline.
22
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The seabirds index in England in 2015 continues to show a different pattern to the UK index6. One reason for this difference is species composition. Some species breed only in Scotland whereas others are more widespread but have the bulk of their populations in northern parts of the British Isles, and there may be insufficient data to generate an England-only trend. Furthermore, it was also possible to generate an England trend for gannet based on reliable data from a single large colony, but there are insufficient data representative of the UK population to produce a reliable UK trend for this species.
6
The UK seabird trend can be seen in the Defra National Statistics Release, Wild bird populations in the UK, 1970-2013, also published today.
24
6. Wintering waterbird populations in England Waterbird refers to birds that inhabit or depend on water, this chapter is about waterbirds that over-winter in England, some of which also breed in England7. In the winter of 2014-15 the wintering waterbird index was 73% higher than 1975-96. The index peaked in the late 1990s, and has declined since, with the smoothed index falling 9% in the short-term between 2008-09 and 2013-14. Figure 6: Breeding wintering water birds in England, 1975/76-2014/15
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line). Data from surveys of wintering waterbirds are based on full counts at colonies or wetland and coastal sites of markedly varying size. This means that bootstrapping methods cannot be applied and that trends for these groups are currently presented without confidence intervals. iii) the number of species in each sub indicator do not sum to the number in the all species indicator because four species are included in all wintering waterbirds but are neither wildfowl nor wader. These are 2 grebes (little and great-crested), one rail species (coot) and cormorant. These are neither wildfowl nor waders but are in three different taxonomic groups none large enough to warrant a separate indicator. They are included in the all wintering waterbird indicator because they behave similarly to wildfowl and are counted in the same way, using the Wetland Bird Survey.
7
Not all of the wintering waterbirds in this chapter are included in the all breeding birds index, only those which also breed in England. In Annex A those species that overlap are included under both.
25
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Main notes: methodological detail, limitations of the indicators and further information 1. The bird population indices have been compiled in conjunction with the British Trust for Ornithology (BTO), the Joint Nature Conservation Committee (JNCC), and the Royal Society for the Protection of Birds (RSPB) from a wide range of sources, principally:
the Common Birds Census (from 1966 to 2000), the BTO/JNCC/RSPB Breeding Bird Survey (from 1994 to 2015), the BTO/ Waterways Bird Survey (from 1974 to 2007), the BTO/Environment Agency for England and Wales (EA) Waterways Breeding Bird Survey (from 1998 to 2013), the BTO/Wildfowl & Wetland Trust/RSPB/JNCC Wetland Bird Survey counts (from 1975-76 to 2014-15), the WWT Goose & Swan Monitoring Programme in partnership with the JNCC and Scottish Natural Heritage, the Seabird Monitoring Programme (from 1986 to 2015), the Periodic Seabird censuses supplied by JNCC, RSPB, the Seabird Group, SOTEAG (Shetland Oil Terminal Environmental Advisory Group) and other partners, Monitoring of scarce and rare breeding birds by the Statutory Conservation Agency and RSPB Annual Breeding Bird Scheme (SCARABBS) and the Rare Breeding Birds Panel.
Regional analysis is published as part of the Breeding Bird Survey. The census sources provide an indication of the average annual rate of change between censuses for some species, and this is assumed to apply to each year between censuses. More information about individual species trends, including photographs, background to the changes in population are available via the BTO website. Some regional analysis is also published as part of the Breeding Bird Survey, including for other constituent countries of the UK. More information about the State of UK birds can be accessed through the RSPB website. Details on the monitoring of scarce and rare breeding birds, including annual reports, can be found on the website of the Rare Breeding Birds Panel. 2. The indices cover birds that are native to the England, excluding rare (less than 300 breeding pairs) and introduced species. The indices portray the annual changes in abundance. Within the indices, each species is given equal weighting, and the overall index is the geometric mean of the individual species indices. Individual species populations within the index may be increasing or decreasing, irrespective of the overall index trends. Species indices are derived by modelling count data and
28
estimates are revised when new data or improved methodologies are developed and applied retrospectively to earlier years. 3. The indices are considered to give reliable medium to long-term trends but strong reliance should not be attached to short-term changes from year to year. 4. The individual species included within each indicator are given in Annex A. 5. Smoothing is a standard procedure in the generation and reporting of bird population trends (www.bto.org/birdtrends2010/methodology.htm). The smoothing methodology involves the application of a thin plate smoothing spline to remove the short-term peaks and troughs due to weather effects and any between year sampling error. Research by the BTO and RSPB further developed this procedure to enable the production of an indicator based on smoothed individual species’ indices. 6. Bootstrapping, a standard statistical technique, is used to calculate 95% confidence intervals in the indicators and in change over any specified period. The width of the confidence interval for a given indicator is influenced by the number of species in that indicator and the precision of the individual species trends that make up that indicator. The precision of trends varies between species; this is true even for species for which trends come from the same source, due to the variation in sample size. Therefore the size of confidence intervals varies among habitat indicators. 7. For the farmland bird index it should be noted that although 20 species were originally chosen for the index, a reliable annual index is not available for barn owl, so that species is excluded. 8. Details of agri-environmental schemes designed to improve environmental management in farming can be found via the following administrating bodies:
Natural England
9. Defra previously also published an annual National Statistics Release, Wild bird population indicators for the English regions. This Release was discontinued in 2011, as a result of resource constraints and changes in regional governance. The last release8 covered trends for 1994 to 2008 and was published in 2010. However, these statistical releases drew upon results from the Joint BTO/JNCC/RSPB Breeding Bird Survey and some regional analysis will continue to be published as part of the Breeding Bird Survey, including for the other constituent countries of the UK.
8
www.defra.gov.uk/statistics/files/wdbrds201004.pdf
29
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Enquiries to Department for Environment, Food and Rural Affairs Nobel House, 17 Smith Square, London, SW1P 3JR Public enquiries: 0208 225 7921 or Press enquiries: 0208 225 7317 Public enquiries & user feedback: [email protected]
Contents Executive summary ............................................................................................................. 1 Why monitor bird populations? ............................................................................................ 2 Understanding the bird population indices ........................................................................... 2 Assessing trends ................................................................................................................. 3 1. Native breeding wild bird populations in England ............................................................ 5 2. Breeding farmland bird populations in England ............................................................... 8 3. Breeding woodland bird populations in England ............................................................ 12 4. Breeding water and wetland bird populations in England .............................................. 16 5. Breeding seabird populations in England....................................................................... 22 6. Wintering waterbird populations in England ................................................................... 25 Main notes: methodological detail, limitations of the indicators and further information ..... 28 Annex A: Trends in bird species, by habitat group, in England .......................................... 30
© Crown copyright 2017 You may re-use this information (excluding logos) free of charge in any format or medium, under the terms of the Open Government Licence v.3. To view this licence visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/, or email [email protected]. All photos are copyright © Natural England https://www.flickr.com/photos/naturalengland/albums/72157627865255667/with/94989772 11/ PB 14463
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Why monitor bird populations? Bird populations have long been considered to provide a good indication of the broad state of wildlife in England. This is because they occupy a wide range of habitats and respond to environmental pressures that also operate on other groups of wildlife. In addition, there are considerable long-term data on trends in bird populations, allowing for comparison between short-term and long-term. Because they are a well-studied taxonomic group, drivers of change for birds are better understood than for other species groups, which enables better interpretation of any observed changes. Birds also have huge cultural importance and are highly valued as a part of England’s natural environment by the general public. However, the bird indicators presented in this publication are not intended, in isolation, as indicators of the health of the natural environment more widely. It is not possible to determine changes in the actual number of birds for each species in England each year, it is possible to estimate the relative change, from counts on sample plots surveyed as part of a range of national monitoring schemes1. Trends in bird populations are used by policy makers, government agencies and nongovernmental organisations as part of the evidence base to assess the effects of environmental management, such as agricultural practices, on bird populations. The trends are also used to assess the effectiveness of environmental interventions intended to address declines, such as agri-environment schemes targeted at farmland birds.
Understanding the bird population indices Individual bird species population trends, based on expert surveys, are calculated as an index. This relates the population in a given year to a ‘baseline’ – the first year that data are available – which is given a value of 100. Thereafter, the index is expressing the population as a percentage of this ‘baseline’. This annual Defra National Statistics Release presents data trends up to 2015 in populations of common birds (species with a population of at least 300 breeding pairs) that are native to, and breed in, England, with trends overall and for four main habitat groups (see Annex A for a list of birds in each group). The release also presents trends for wintering waterbirds, some of which also breed in England. The charts presented combine individual species indices2 into a single indicator to provide an overall trend for each group mentioned above. The indices are considered to give
1
See ‘Main notes’ at the end for more details of the surveys sources used. th Using a geometric mean - an average calculated by multiplying a set of index values and taking the n root, where n is the number of index values. More information can be found in Introduction to the Wild Birds Population Indicator. 2
2
reliable medium to long-term trends but strong reliance should not be attached to shortterm changes from year to year.
Assessing trends Two trends are referred to in the text: the unsmoothed indices show year-to-year fluctuation in populations, reflecting the observed changes in the survey results, and smoothed trends3, which are used to formally assess the statistical significance of change over time. Smoothed trends4 are used for both long and short-term assessments as they reduce the short-term peaks and troughs resulting from, for example, year to year weather and sampling variations. The most recent year of data, i.e. 2015 in this update, is likely to change due to the smoothing process following the inclusion of 2016 data in next year’s update. As a result it is not appropriate to make assessments based on this figure. Where results from the smoothed indices are quoted, this is clearly indicated. These trends are based on estimates from surveys. Smoothed trends are presented with 95% confidence intervals (CI), which are a measure of the precision of these survey estimates: a 95% CI means we are 95% confident that the true value of an indicator in a given year falls within the confidence interval around it. The size of confidence intervals varies among habitat indicators because the width of the confidence interval is influenced by the number of species in each indicator and the precision of the individual species trends that make up the indicator. The precision of trends varies due to differences in sample size. Throughout this release, assessment periods are referred to as:
‘Long-term’ – an assessment of change since the earliest date for which data are available; this varies among habitat indicators and among individual species. ‘Short-term’ – an assessment of change over the latest five years (2009-2014).
Annex A shows long-term and short-term assessments for each individual bird species.
3
There are currently no smoothed trends available for seabirds. See analytical methods on BTO website (www.bto.org/birdtrends2011/methodology.htm) Fewster et al. 2000. Ecology 81: 1970-84. 4
3
Alongside the overall index, the percentage of species within each indicator that have increased or decreased in the long-term and in the short-term is also shown. This is based on the rate of annual change over the long or short-term, categorised by how much the population would change if that annual change continued for 25 years. The bar chart illustrates the percentage of species falling into each category: Strong increase: population increase above 50% increase Weak increase: above 33% but less than 50% increase No change: between a 25% decrease and a 33% increase Weak decline: less than 50% but greater than 25% decrease Strong decline: population decrease of 50% These thresholds are asymmetrical to represent symmetrical proportional change in an index. These thresholds are used in the formal, Government endorsed, Birds of Conservation Concern5 status assessment for birds in the UK. The bird population indices have been compiled in conjunction with the Royal Society for the Protection of Birds (RSPB), the British Trust for Ornithology (BTO) and the Joint Nature Conservation Committee (JNCC).
5
See the BTO website (http://www.bto.org/volunteer-surveys/birdtrack/bird-recording/birds-conservationconcern)
4
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Species breakdown The all-species index comprises of 118 species of birds, of all widespread species, with populations of at least 300 breeding pairs for which we have sufficient data. Species trends within this index vary widely, from species increasing several-fold (e.g. blackcap, buzzard, cetti’s warbler, great spotted woodpecker, and collared dove) to those having declined to less than a tenth of 1970 levels (turtle dove, tree sparrow, willow tit and grey partridge). The main patterns and drivers of change are considered by looking at the indices of species grouped by habitat in Figure 1b and the following chapters. Figure 1b: Populations of wild birds in England by habitat, 1970-2015
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2. Breeding farmland bird populations in England Farmland refers to the large proportion of England which is devoted to agriculture and consists of fields and grasslands habitat. Farmland also provides semi-natural habitats such as hedgerows and field margins that provide food and shelter to birds. In 2015 the England farmland bird index was less than half its 1970 value. The majority of this decline occurred between the late seventies and early eighties largely due to the impact of rapid changes in farmland management during this period. More recently, since 1990, the decline has slowed; the smoothed index decreased by 7% between 2009 and 2014. Figure 2: Breeding farmland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
Long-term Since 1970, 21% of species in the indicator showed a weak increase, 26% showed no change and 53% showed either a weak or a strong decline. Short-term Over the short-term period between 2009 and 2014, 42% of species in the indicator showed an increase, 26% showed no change and 32% showed a decline.
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Factors affecting farmland bird populations The large declines in the abundance of some farmland birds have many known and potential causes. Many of the declines have been caused by land management changes and the intensification of farming that took place since the 1950s and 60s, such as the loss of mixed farming, a move from spring to autumn sowing of arable crops, change in grassland management (e.g. a switch from hay to silage production), increased pesticide and fertiliser use, and the removal of non-cropped features such as hedgerows. The rate of these changes, which resulted in the loss of suitable nesting and suitable feeding habitats, and a reduction in available food, was greatest during the late 1970s and early 1980s, the period during which many farmland bird populations declined most rapidly. Some farming practices still have negative impacts on bird populations, but most farmers can and do take positive steps to conserve birds on their land. In particular, a number of incentive schemes encourage improved environmental stewardship in farming, with some measures specifically designed to help stabilise and recover farmland bird populations. These include the provision of over-wintered stubbles and planted wild bird crop covers to provide seed in the winter, uncropped margins on arable fields and sympathetic management of hedgerows. Changes in numbers experienced by some species may, to a lesser extent, be further driven by other pressures. For example, there is evidence of an adverse impact for some species from disease. Species breakdown The farmland bird index comprises 19 species of bird. The long-term decline of farmland birds in England has been driven mainly by the decline of those species that are restricted to, or highly dependent on, farmland habitats (the ‘specialists’). Between 1970 and 2015, the farmland specialists index declined by 71% while farmland generalists increased by 3%. Both smoothed trends showed declines, of 72% and 4% respectively (figure 2a). Figure 2a: Breeding farmland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trends (dashed lines) and smoothed trends (solid lines).
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3. Breeding woodland bird populations in England Woodland trees provide nesting for birds as well as foraging opportunities and cover from predators. In 2015 the breeding woodland bird indicator for England was 21% lower than in 1970. The greatest decline occurred between the early eighties and the early nineties, since 1996 the index has been more stable. Over the past 10 years the woodland bird index has showed no significant change despite some yearly fluctuations. Figure 3: Breeding woodland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
Long-term Since 1970, 26% of woodland species have increased in number, 45% showed no change and 29% declined, the majority of these showed a strong decline. Short-term Over the short-term period between 2009 and 2014, 32% of species showed an increase, 29% showed no change and 38% showed a decline. In contrast to over the long-term, the majority of declining species showed weak rather than strong decline. A number of species showed a long-term trend of no change, but a weak decline in the short-term such as the chaffinch, garden warbler and the long tailed tit. A few species showed strong decline in the long-term but weak decline in the short-term: marsh tit, willow tit. In contrast, lesser redpoll showed strong increase in the short-term, after a long-term trend of a strong decline. 12
Factors affecting woodland birds The declines in woodland birds have several known and potential causes, such as a lack of woodland management and increased deer browsing pressure, both of which result in a reduced diversity of woodland structure and, reduced availability of suitable nesting and foraging habitats. In addition, several declining woodland birds are long-distance migrants, and a decline in the extent or quality of habitats used outside the breeding season may be one factor affecting these species outside of England.
Species breakdown The woodland bird index comprises 34 species of bird. The relatively stable trend for all woodland birds from the late -1990s masks different underlying trends for: specialist species, which are highly dependent on woodland habitats; and generalist species, which are found in a wide range of habitats, including woodland. The long-term decline of woodland birds in England has been mostly driven by the decline of specialist woodland birds. Between 1970 and 2015, the index for woodland specialists declined by 34% while the woodland generalist index showed little change. The smoothed trend shows a decline of 36% for specialists and no significant change for generalists (figure 3a). Figure 3a: Breeding woodland birds in England, 1970-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trends (dashed lines) and smoothed trends (solid lines).
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4. Breeding water and wetland bird populations in England Water and wetlands include rivers, lakes, ponds, reedbeds, grazing marshes and lowland raised bogs, all providing important habitats for birds. Water and wetland bird numbers have remained fairly stable for most of the period since data collection started in 1975. In 2015 the water and wetland bird index exceeded it’s 1975 level by 8%. Numbers rose slightly in the early 2000s but more recently the smoothed index showed a significant decline of 5% between 2009 and 2014. Figure 4: Breeding water and wetland birds in England, 1975-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
Long-term For the 25 species for which a long-term trend can be calculated, 32% of species showed an increase, 40% showed no change and 28% showed a decline, the majority of species exhibiting a change showed a weak rather than a strong change. For little egret, data collection started in 2004 and therefore a long-term trend could not be calculated (for more information on the time series used for different species long-term trends, see Annex A).
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Short-term Over the short-term period between 2009 and 2014, 23% of species showed an increase, 23% showed no change and 54% showed a decline. This change in trend was mostly caused by a large number of species moving down one category (e.g. weak increase to no change) rather than large changes in the species trends over time. Factors affecting water and wetland bird populations The historical declines in breeding waders, resulted from land management changes such as drainage, the intensification of grassland management and the conversion of coastal and floodplain grazing marshes to arable land. Where populations persist in small fragments of high quality habitat, their nests and young are vulnerable to predation, which is currently thought to be limiting the recovery of several species of breeding wader. Species breakdown The 26 species of bird included in the water and wetland bird index can be split into four sub-habitat indicators. Although the all species index shows a relatively stable trend this masks underlying differences between sub-habitat indicators (figure 4a). When interpreting these trends it should be borne in mind that each sub-habitat trend is derived from relatively few species trends. Figure 4a: Breeding water and wetland birds in England, 1975-2015
Note: i) figures in brackets show the number of species, ii) graph shows unsmoothed trends (dashed lines) and smoothed trends (solid lines),
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5. Breeding seabird populations in England The English coast consists of a wide variety of habitats such as sea cliffs, sand dunes, shingle ridges and machair and intertidal areas. In 2015, the breeding seabird index in England was 22% higher than in 1986, the highest level ever recorded. Despite fluctuations the indicator has increased steadily since the late nineties driven mainly by subsurface piscivore species. Figure 5: Breeding seabirds in England, 1986-2015
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (solid line) - no smoothed trend is available for seabirds as individual species population trends are based on census data.
Long-term Between 1986 and 2014, 27% of 11 seabird species showed an increase, 45% showed no change and 27% showed either a weak or a strong decline. Short-term Over the short-term period between 2009 and 2014, 45% of species showed an increase, 18% showed no change and 36% showed a decline.
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The seabirds index in England in 2015 continues to show a different pattern to the UK index6. One reason for this difference is species composition. Some species breed only in Scotland whereas others are more widespread but have the bulk of their populations in northern parts of the British Isles, and there may be insufficient data to generate an England-only trend. Furthermore, it was also possible to generate an England trend for gannet based on reliable data from a single large colony, but there are insufficient data representative of the UK population to produce a reliable UK trend for this species.
6
The UK seabird trend can be seen in the Defra National Statistics Release, Wild bird populations in the UK, 1970-2013, also published today.
24
6. Wintering waterbird populations in England Waterbird refers to birds that inhabit or depend on water, this chapter is about waterbirds that over-winter in England, some of which also breed in England7. In the winter of 2014-15 the wintering waterbird index was 73% higher than 1975-96. The index peaked in the late 1990s, and has declined since, with the smoothed index falling 9% in the short-term between 2008-09 and 2013-14. Figure 6: Breeding wintering water birds in England, 1975/76-2014/15
Note: i) figures in brackets show the number of species. ii) graph shows unsmoothed trend (dashed line) and smoothed trend (solid line). Data from surveys of wintering waterbirds are based on full counts at colonies or wetland and coastal sites of markedly varying size. This means that bootstrapping methods cannot be applied and that trends for these groups are currently presented without confidence intervals. iii) the number of species in each sub indicator do not sum to the number in the all species indicator because four species are included in all wintering waterbirds but are neither wildfowl nor wader. These are 2 grebes (little and great-crested), one rail species (coot) and cormorant. These are neither wildfowl nor waders but are in three different taxonomic groups none large enough to warrant a separate indicator. They are included in the all wintering waterbird indicator because they behave similarly to wildfowl and are counted in the same way, using the Wetland Bird Survey.
7
Not all of the wintering waterbirds in this chapter are included in the all breeding birds index, only those which also breed in England. In Annex A those species that overlap are included under both.
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Main notes: methodological detail, limitations of the indicators and further information 1. The bird population indices have been compiled in conjunction with the British Trust for Ornithology (BTO), the Joint Nature Conservation Committee (JNCC), and the Royal Society for the Protection of Birds (RSPB) from a wide range of sources, principally:
the Common Birds Census (from 1966 to 2000), the BTO/JNCC/RSPB Breeding Bird Survey (from 1994 to 2015), the BTO/ Waterways Bird Survey (from 1974 to 2007), the BTO/Environment Agency for England and Wales (EA) Waterways Breeding Bird Survey (from 1998 to 2013), the BTO/Wildfowl & Wetland Trust/RSPB/JNCC Wetland Bird Survey counts (from 1975-76 to 2014-15), the WWT Goose & Swan Monitoring Programme in partnership with the JNCC and Scottish Natural Heritage, the Seabird Monitoring Programme (from 1986 to 2015), the Periodic Seabird censuses supplied by JNCC, RSPB, the Seabird Group, SOTEAG (Shetland Oil Terminal Environmental Advisory Group) and other partners, Monitoring of scarce and rare breeding birds by the Statutory Conservation Agency and RSPB Annual Breeding Bird Scheme (SCARABBS) and the Rare Breeding Birds Panel.
Regional analysis is published as part of the Breeding Bird Survey. The census sources provide an indication of the average annual rate of change between censuses for some species, and this is assumed to apply to each year between censuses. More information about individual species trends, including photographs, background to the changes in population are available via the BTO website. Some regional analysis is also published as part of the Breeding Bird Survey, including for other constituent countries of the UK. More information about the State of UK birds can be accessed through the RSPB website. Details on the monitoring of scarce and rare breeding birds, including annual reports, can be found on the website of the Rare Breeding Birds Panel. 2. The indices cover birds that are native to the England, excluding rare (less than 300 breeding pairs) and introduced species. The indices portray the annual changes in abundance. Within the indices, each species is given equal weighting, and the overall index is the geometric mean of the individual species indices. Individual species populations within the index may be increasing or decreasing, irrespective of the overall index trends. Species indices are derived by modelling count data and
28
estimates are revised when new data or improved methodologies are developed and applied retrospectively to earlier years. 3. The indices are considered to give reliable medium to long-term trends but strong reliance should not be attached to short-term changes from year to year. 4. The individual species included within each indicator are given in Annex A. 5. Smoothing is a standard procedure in the generation and reporting of bird population trends (www.bto.org/birdtrends2010/methodology.htm). The smoothing methodology involves the application of a thin plate smoothing spline to remove the short-term peaks and troughs due to weather effects and any between year sampling error. Research by the BTO and RSPB further developed this procedure to enable the production of an indicator based on smoothed individual species’ indices. 6. Bootstrapping, a standard statistical technique, is used to calculate 95% confidence intervals in the indicators and in change over any specified period. The width of the confidence interval for a given indicator is influenced by the number of species in that indicator and the precision of the individual species trends that make up that indicator. The precision of trends varies between species; this is true even for species for which trends come from the same source, due to the variation in sample size. Therefore the size of confidence intervals varies among habitat indicators. 7. For the farmland bird index it should be noted that although 20 species were originally chosen for the index, a reliable annual index is not available for barn owl, so that species is excluded. 8. Details of agri-environmental schemes designed to improve environmental management in farming can be found via the following administrating bodies:
Natural England
9. Defra previously also published an annual National Statistics Release, Wild bird population indicators for the English regions. This Release was discontinued in 2011, as a result of resource constraints and changes in regional governance. The last release8 covered trends for 1994 to 2008 and was published in 2010. However, these statistical releases drew upon results from the Joint BTO/JNCC/RSPB Breeding Bird Survey and some regional analysis will continue to be published as part of the Breeding Bird Survey, including for the other constituent countries of the UK.
8
www.defra.gov.uk/statistics/files/wdbrds201004.pdf
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