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C6. Insects of the wider countryside (butterflies)
http://jncc.defra.gov.uk/page-4236
C6. Insects of the wider countryside (butterflies)
a. Semi-natural habitat specialists
b. Species of the wider countryside
Type: State Indicator
Summary
Figure C6ai. Trends in butterfly populations in the UK: habitat specialists, 1976 to 2014.
Notes:
1. The figure in brackets shows the number of species included in the index.
2. The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line)
with its 95 per cent confidence interval (shaded).
3. The bar chart shows the percentage of species within the indicator that have shown a
statistically significant increase, statistically significant decrease, or no change.
Source: Butterfly Conservation, Centre for Ecology & Hydrology, Defra, Joint Nature Conservation
Committee.
Figure C6bi. Trends in butterfly populations in the UK: species of the wider countryside, 1976
to 2014.
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C6. Insects of the wider countryside (butterflies)
http://jncc.defra.gov.uk/page-4236
Notes:
1. The figure in brackets shows the number of species included in the index.
2. The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line)
with its 95 per cent confidence interval (shaded).
3. The bar chart shows the percentage of species within the indicator that have shown a
statistically significant increase, statistically significant decrease, or no change.
4. Since 2013, an improved analysis method has been applied to the measure for species of
the wider countryside (see ‘Background’ section for further information).
Source: Butterfly Conservation, Centre for Ecology & Hydrology, Defra, Joint Nature Conservation
Committee.
Assessment of change in butterfly populations
Long term
Short term
Semi-natural habitat specialists
Latest year
Increased (2014)
1976–2014
Species of the wider countryside
2009–2014
Decreased (2014)
1976–2014
2009–2014
Notes: While percentage changes in these indices are reported based on the most recent
unsmoothed data point (2014), the formal long-term and short-term assessments of the statistical
significance of these changes are made using the smoothed data to 2014. Analysis of the underlying
trends is undertaken by the data providers.

Since 1976, the indices for butterflies strongly associated with semi-natural habitats (habitat
specialists) and for those found in the wider countryside have decreased by 61 per cent and 41 per
cent respectively.

Large fluctuations in numbers between years are typical features of butterfly populations. The
statistical assessment of change is therefore made on an analysis of the underlying smoothed
trends.
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C6. Insects of the wider countryside (butterflies)
http://jncc.defra.gov.uk/page-4236

This analysis shows that, since 1976, populations of habitat specialists and species of the wider
countryside have declined significantly.

The unsmoothed data for habitat specialists show an increase between 2009 and 2014, whilst
species of the wider countryside show a decrease over the same period. However, the underlying
analysis of the smoothed trend shows that these increases are not significant; there has been no
overall change in either of the two indices in the five years to 2014.

In the most recent year, 2014, habitat specialist butterflies increased by 6.7 per cent from the
previous year, whilst wider countryside species decreased by 8.0 per cent.
Indicator description
The indicator consists of two measures of annual butterfly population abundance: the first for
specialist butterflies (species strongly associated with semi-natural habitats such as unimproved
grassland) and the second for butterflies found in both semi-natural habitats and the wider
countryside. Both measures show marked fluctuations from year to year, principally in response to
weather conditions. For this reason, the assessment of change is based on an analysis of underlying
smoothed trends and undertaken by Butterfly Conservation and the Centre for Ecology & Hydrology.
The species of the wider countryside index decreased by 41 per cent between 1976 and 2014; the
underlying analysis indicates that this decrease was chiefly due to a statistically significant reduction
in relative abundance over the period 1976 to 2002. The index showed a decrease over the period
2009 to 2014, from 61 per cent to 59 per cent of the 1976 level. However, this change is not
statistically significant and an amber assessment is assigned to the measure in the short term.
Habitat specialist species, which are vulnerable to semi-natural habitat loss and fragmentation, have
not recovered from population declines experienced in the late 1970s, attributed mainly to drought
conditions in 1976. The habitat specialist index has declined by 61 per cent between 1976 and 2014.
The underlying analysis shows that this decrease was due to a statistically significant reduction in
abundance over the period 1976 to 1980. There is some suggestion of recent recovery in habitat
specialists from 2009–2014, with an increase from 35 per cent to 39 per cent of the 1976 level.
However, the change since 2009 is not statistically significant and an amber assessment is assigned
to the measure in the short term.
Relevance
Butterflies respond rapidly to changes in environmental conditions and habitat management, occur in
a wide range of habitats, and are representative of many other insects, in that they utilise areas with
abundant plant food resources. Butterflies are complementary to birds and bats as an indicator,
especially the habitat specialists, because they use resources in the landscape at a much finer spatial
scale than either of these groups.
Background
This indicator is a multi-species index compiled by Butterfly Conservation (BC) and the Centre for
Ecology & Hydrology (CEH) from data collated through the UK Butterfly Monitoring Scheme (UKBMS)
and, for the wider countryside measure, the Wider Countryside Butterfly Monitoring Scheme (WCBS).
The indicator shows individual measures for 26 habitat specialist butterflies (low mobility species
restricted to semi-natural habitats) and 25 butterflies which use habitats across the wider countryside
using data collected at 4,040 sites (Figure C6i). The wider countryside measure, however, includes
24 trends, as an aggregate trend is used for Small Skipper (Thymelicus lineola) and Essex skipper
(Thymelicus sylvestris), which have been combined due to difficulties in distinguishing them in the
field.
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C6. Insects of the wider countryside (butterflies)
http://jncc.defra.gov.uk/page-4236
The year-to-year fluctuations of butterflies are often linked to natural environmental variation,
especially weather conditions. To identify underlying patterns in population trends, the assessment of
change is based on smoothed indices. The smoothed trend in the multi-species indicator is assessed
by structural time-series analysis. A statistical test is performed using the software TrendSpotter to
compare the difference in the smoothed index in the latest year versus other years in the series.
Within the measures, each individual species trend is given equal weight, and the annual figure is the
geometric mean of the component species indices for that year. Populations of individual species
within each measure may be increasing or decreasing, irrespective of the overall trends. The bar
chart provided alongside each habitat chart above shows the percentage of species within that
indicator that have shown a statistically significant increase, a statistically significant decrease or no
change.
A table listing the species that are included in each index can be found in the Datasheet. For each
species, an estimate of change in the long-term and in the short-term is given, as well as an
assessment of whether the species trend is increasing or decreasing.
Since 2013, an improved analytical method has been applied to the measure for species of the wider
countryside. The new method makes more efficient use of available data to generate more precise
and representative indices and trends. The new method uses all butterfly counts collected at both
UKBMS sites (2,383 compared with 2,330 in 2013) and randomly selected 1km squares of the Wider
Countryside Butterfly Survey (1,657). The method uses all butterfly counts in a season to estimate
the seasonal pattern of butterfly counts for that year, and uses this to weight observed counts when
calculating annual population indices. Further details of the method can be found in Dennis et al.
(2013). The new trend for species of the wider countryside is similar to that generated through the old
analysis, though population indices are at times lower as on average additional wider countryside
sample sites support lower densities of butterflies. In 2015, the site index only data was incorporated
into the models; these data are most prevalent in earlier years and thus the graphs are slightly
different to those previously presented.
As there are delays in data submission, data for previous years are also updated retrospectively; in
2014 extra data were added for 2012 and 2013, for example. This means that the species indices for
individual years may vary from previous publications.
Further details of the methods used can be found on the UK Butterfly Monitoring Scheme website and
in the technical background paper provided at the end of this indicator.
Figure C6i. Locations of the 2,383 UK Butterfly Monitoring Scheme sites (blue) and 1,657
Wider Countryside Butterfly Monitoring Scheme squares (red).
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C6. Insects of the wider countryside (butterflies)
http://jncc.defra.gov.uk/page-4236
Further development planned
Development of country and regional breakdowns is ongoing. There are also plans to implement
smoothing by using Generalised Additive Models, the technique adopted for birds and bats, to make
the assessments more comparable between indicators. The indicator may be further revised if
improved methodologies are developed and applied retrospectively to earlier years.
Goals and targets
Aichi Targets for which this is a primary indicator
Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.
Target 7: By 2020, areas under agriculture, aquaculture and forestry are managed
sustainably, ensuring conservation of biodiversity.
Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and
genetic diversity.
Target 12: By 2020, the extinction of known threatened species has been prevented and
their conservation status, particularly of those most in decline, has been improved and sustained.
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C6. Insects of the wider countryside (butterflies)
http://jncc.defra.gov.uk/page-4236
Aichi Targets for which this is a relevant indicator
Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.
Target 5: By 2020, the rate of loss of all natural habitats, including forests, is at least
halved and where feasible brought close to zero, and degradation and fragmentation is significantly
reduced.
Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and
genetic diversity.
Target 11: By 2020, at least 17 per cent of terrestrial and inland water, and 10 per cent of
coastal and marine areas, especially areas of particular importance for biodiversity and ecosystem
services, are conserved through effectively and equitably managed, ecologically representative and
well connected systems of protected areas and other effective area-based conservation measures,
and integrated into the wider landscape and seascapes.
Web links for further information
Reference
UK Butterfly Monitoring
Scheme
Title
Website
Butterflies as
indicators
http://www.ukbms.org/indicators.aspx
References
Dennis, E.B., Freeman, S.N., Brereton, T. & Roy, D.B. 2013. Indexing butterfly abundance whilst accounting
for missing counts and variability in seasonal pattern. Methods in Ecology and Evolution, 4(7), 637–645.
Download Datasheet
Download Technical background paper
Last updated: October 2015
Latest data available: 2014
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