The UK Government has released a report assessing bird populations across the UK between 1970 and 2015 particularly in selected and vulnerable groups: farmland, woodland, water and seabirds
Why should governments monitor bird populations?
Bird populations have long been considered to provide a good indication of the broad state of wildlife in the UK. 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 the UK’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 the UK each year, it is possible to estimate the relative change, from counts on sample plots surveyed as part of a range of national monitoring schemes just as Birds On The Edge and others do in Jersey.
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 500 breeding pairs) that are native to, and breed in, the UK, with trends overall and for four main habitat groups (see Annex A in the report for a list of birds in each group). The release also presents trends for wintering waterbirds, some of which also breed in the UK. The charts presented combine individual species indices into a single indicator to provide an overall trend for each group mentioned above. 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.
Assessing the 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 trends, which are used to formally assess the statistical significance of change over time. Smoothed trends 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.
The combined all species index has changed little compared with 40 years ago in the UK, however, this masks considerable flux, with some species increasing and some species decreasing in population size. These changes in relative abundance tend to cancel each other out in the combined index.
- The all-species index in the UK was 2% below its 1970 value
- There were less than half the number of farmland birds than in 1970, most of this decline occurred between the late seventies and early eighties
- There were 18% less woodland birds than in 1970
- Water and wetland bird numbers were 7% lower than in 1975
- There were 22% less seabirds compared to 1986
- The number of wintering waterbirds was 88% higher than in 1975-76, the index peaked in 2001 and has declined since.
Between 2009 and 2014:
- The smoothed all species index remained level
- Farmland birds smoothed index decreased 8%
- The number of woodland birds did not change significantly, although the unsmoothed index dipped to the lowest figure ever recorded in 2013 before recovering
- The smoothed water and wetland bird index declined by 7%
- The number of seabirds declined 6%, in 2013 numbers dipped to the lowest ever but have since increased slightly
- The smoothed wintering water bird index fell 8%.
Download the report Wild bird populations in the UK, 1970-2015 here