Figure C8i. Trends in widespread bat populations,
1999 to 2011.
Notes: The headline measure
is a composite index of six species: Daubenton's bat, noctule,
serotine, lesser horseshoe bat, common pipistrelle and soprano
Source: Bat Conservation
Notes: Estimates for
combined (common and soprano) pipistrelle,
1978–1992. Although based on limited data, this
places the more recent trends in a longer-term context.
Source: Bat Conservation
Trust. Data from: Harris, S., Morris, P., Wray, S. and Yalden, D.
1995. A review of British mammals: population estimates and
conservation status of British mammals other than cetaceans.
Assessment of change in widespread bat
- Bat populations are considered to be a good indicator of the
broad state of wildlife and landscape quality because they utilise
a range of habitats across the landscape and are sensitive to
pressures in the urban, suburban and rural environment.
- Bats have undergone severe declines historically. However since
2000, bat populations have increased by 17 per cent.
The indicator shows changes in the population size of six
widespread bat species, based on summer field surveys and colony
counts and winter hibernation counts. Assessment is based on
the analysis of these trends, using a statistical model developed
by the Bat Conservation Trust. Since 2000, the populations have
increased by 17 per cent, giving an ‘improving’ assessment.
Bats experienced major declines during the latter half of the
20th century. In response to these declines, large-scale
national monitoring was put in place so that future changes could
be detected. Bats have benefited from strict legal
protection, direct conservation action and public education, but
remain vulnerable to pressures such as landscape change and
development. A significant increase in the lesser horseshoe
bat (Rhinolophus hipposideros) population underpins this
positive trend and has been attributed to conservation measures and
a series of mild winters that have enhanced winter survival.
The lesser horseshoe bat increase has been sustained throughout the
period of the indicator. The dip in the indicator in
2011 is due to lower colony counts of serotines (Eptesicus
serotinus) and soprano pipistrelles (Pipistrellus
pygmaeus) and lower encounter rates of noctules (Nyctalus
noctula) in the field survey.
All bats and their roosts are protected by
domestic and European legislation. The UK is a signatory to
the EUROBATs agreement, set up under the Convention on Migratory
Species, with the intention of conserving all European bat
In 2011, National Bat Monitoring Programme
(NBMP) data were used alongside datasets from eight other European
countries to construct a prototype European indicator of population
trends in hibernating bats, a project funded by European
Environment Agency (EEA). The development of a European
indicator provides additional context for the interpretation of
national species trends. It is planned to expand the European
indicator to include 15 or more countries in the near future.
Bat species make up a third of the UK’s mammal fauna and
occur in most lowland habitats across the UK. The species used in
this index are widespread throughout a variety of landscapes
including urban areas, farmland, woodland, and river/lake systems.
All bats in the UK feed at night and prey on insects. In
order to thrive they require adequate roosting opportunities
(particularly for breeding and hibernating), foraging habitat and
connected landscape features, such as hedgerows and tree lines that
assist them in commuting between roost sites and feeding
locations. Key pressures on bats (landscape change,
agricultural intensification, development, habitat fragmentation)
are also relevant to many other wildlife groups. Bats are
sensitive to pollution and factors affecting their insect prey
(e.g. pesticides, drainage, land management change). Climatic
shifts are predicted to affect bat populations through changes in
their yearly hibernation cycles, breeding success and food
The indicator has been compiled by the Bat Conservation Trust
(BCT) using data collected annually from the National Bat
Monitoring Programme (NBMP). This delivers trends for 11 of
the UK’s 17 resident bat species by deploying a network of over
2,300 volunteers to record observations at over 5,000 sites.
The indicator is a composite index which combines population
trend data for six widespread species. Surveys for these
species include summer roost (colony) counts, visual and/or
acoustic observations along predetermined transects within 1km
randomly selected survey grids or along 1km sections of waterway,
and counts at hibernation sites. Most of the species are
surveyed by two of the three methods, all of which are included in
the index. The index is presented independent of habitat, but
the predominant habitat types represented in the combined dataset
are woodland (broad-leaf and conifer), farmland (arable and
grassland), urban and waterway (rivers, streams and canals).
The locations of monitoring sites for the six index species are
shown in Figure C8iii.
For each species, Generalised Additive Modelling (GAM) is used
to calculate the trends in numbers over time. The models
include terms for factors that can influence the apparent
population means (e.g. bat acoustic detector model, temperature,
etc), so their effect can be taken into account. For easier
interpretation the means are then converted to an index that is set
to 100 for the selected baseline year of data. The species
indices are revised when new data become available or when improved
modelling methods are developed and applied retrospectively to
earlier years. To generate the overall composite bat
indicator, each of the six species has been given equal weighting,
and the annual index figure is the geometric mean in that year.
The GAM models produce smoothed trends with confidence
intervals which are the basis of the indicator assessment (Figure
Table C8i. Species used in the bat indicator.
serotine (Eptesicus serotinus)
Habitats Directive Annex IV
Daubenton’s bat (Myotis daubentonii)
Habitats Directive Annex IV
noctule (Nyctalus noctula)
Habitats Directive Annex IV. UK BAP species from 2007
common pipistrelle (Pipistrellus pipistrellus)
Habitats Directive Annex IV. UK BAP species until 2007
soprano pipistrelle (Pipistrellus pygmaeus)
Habitats Directive Annex IV. UK BAP species
lesser horseshoe bat (Rhinolophus hipposideros)
Habitats Directive Annexes II & IV. UK BAP species
Figure C8ii. Generalised Additive Modelling trend in bat
populations, 1999 to 2011.
Notes: Composite index of six
species;:Daubenton's bat, noctule, serotine, lesser horseshoe bat,
common pipistrelle and soprano pipistrelle. This version of
the composite index has been smoothed to help control for random,
between year variation, and to show the overall trend more clearly.
Between year, 95% confidence intervals have also been
calculated and plotted to show that the value of the index in 2011
is significantly larger than in 1999.
Source: Bat Conservation Trust.
Figure C8iii. Location of monitoring sites.
Further development planned
Work is underway to revise the UK indicators for threatened and
widespread species and the indicator is likely to be refined or
augmented in future years, so that the indicator set represents a
wider range of species.
Methods to produce population trend indicators for bats in major
UK landscapes (e.g. woodland, farmland and urban) will be explored
in 2012. Efforts to extend the survey network to deliver
trends and indicators at country level are
Goals and targets
Aichi Targets for which this is a primary
Aichi Targets for which this is a relevant
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.
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
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.
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.
Target 13: By
2020, the genetic diversity of cultivated plants and farmed and
domesticated animals and of wild relatives, including other
socio-economically as well as culturally valuable species, is
maintained, and strategies have been developed and implemented for
minimizing genetic erosion and safeguarding their genetic
Strategic Goal D. Enhance the benefits to all
from biodiversity and ecosystems.
Target 14: By
2020, ecosystems that provide essential services, including
services related to water, and contribute to health, livelihoods
and well-being, are restored and safeguarded, taking into account
the needs of women, indigenous and local communities, and the poor
Target 15: By
2020, ecosystem resilience and the contribution of biodiversity to
carbon stocks has been enhanced, through conservation and
restoration, including restoration of at least 15 per cent of
degraded ecosystems, thereby contributing to climate change
mitigation and adaptation and to combating desertification.