C8. Mammals of the wider countryside (bats)


Type: State Indicator



Figure C8i.  Trends in bat populations, 1999 to 2014.

Figure C8i. Trends in bat populations, 1999 to 2014.


  1. The headline measure is a composite index of eight bat species: serotine, Daubenton's bat, Natterer’s bat, noctule, common pipistrelle, soprano pipistrelle, brown long-eared bat, and lesser horseshoe bat.
  2. The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
  3. The bar chart shows the percentage of species which, over the time periods of the long-term or short-term assessments, have shown a statistically significant increase or decline.

Source: Bat Conservation Trust.


Assessment of change in widespread bat populations


Long term

Short term

Latest year

Bat populations

2010 indicator improving

2010 indicator stable

Decreased (2014)

Note: Long-term and short-term assessments are made on the basis of smoothed trends to the penultimate year (2013) by the Bat Conservation Trust.  This is because the most recent smoothed data point (2014) is likely to change in next year’s update when additional data are included for 2015.  The latest year assessment is based on unsmoothed data.



  • Between 1999, when trends from standardised large-scale monitoring became available through the National Bat Monitoring Programme (NBMP), and 2013, bat populations have increased by 23 per cent; an assessment of the underlying smoothed trend shows this is a statistically significant increase. 
  • In the short term, between 2008 and 2013, an assessment of the underlying smoothed trend shows that bat populations have shown a small, non-significant decrease of 2.5 per cent, and are therefore considered to be stable. 
  • Three species have increased in the long-term: Daubenton’s bat, common pipistrelle and lesser horseshoe bat; no species have decreased; and five species have shown no significant change in population size.  In the short term, between 2008 and 2013, one species, noctule, has shown a significant decrease; two species, common pipistrelle and lesser horseshoe bat, have shown significant increases; and five species have shown no significant change in population size.
  • Fragmented historical evidence suggests that bats underwent severe declines in the latter half of the 20th century.


Indicator description

The indicator shows changes in the population size of eight widespread bat species, based on summer field surveys and roost counts and winter hibernation counts.  Population change between 1999 and 2014 is analysed using a statistical model developed by the Bat Conservation Trust.  The composite index of bat population size has increased significantly in the long term.  The short-term assessment of the indicator, which considers change over the past five years (2008–2013), shows that the trend has stabilised over this period.  Assessments are run to the penultimate year of the trend as the most recent smoothed data point (2014) is likely to change as future years of data are added. There was a dip in the index in 2014 but this result should be treated as provisional for the reason outlined above.



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.  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 populations.  The wider relevance of bats as biodiversity indicators is presented in Jones et al. (2009).



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 (Table C8i) 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.  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 availability. 

Bats experienced major declines throughout Western Europe during the latter half of the 20th century, which have been attributed to agricultural intensification, habitat and roost loss, deliberate killing, remedial timber treatment and insecticide poisoning, and declines of their insect prey.  However bats were relatively understudied in the UK during the period of greatest population loss, and the supporting evidence, synthesised in Haysom et al. (2010), is fragmented.  Evidence includes:

  • reports of the loss of large colonies of several species from traditional roosting sites;
  • a questionnaire survey documenting roost loss, declines in abundance at roosts, and deliberate killing (Racey and Stebbings 1972);
  • range contractions of lesser horseshoe bat (Rhinolophus hipposideros); and
  • a small number of published population trends (e.g. Stebbings 1988; Ransome 1989; Guest et al. 2002).

Figure C8ii is an example historical trend showing decline of combined species of pipistrelle bats in England.  The base point of this graph is set to 100 in 1999 as sample sizes are small in the first few years of the series and the analysis uses only sites with five or more years of data.  The dataset for Figure C8ii pre-dates the separation of pipistrelles into common (Pipistrellus pipistrellus) and soprano pipistrelle (Pipistrellus pygmaeus), and the proportion of each species is unknown in the historical data.  The trend begins in 1977, the earliest year for which there are an acceptable number of sites.  Some caution is necessary in interpreting the decline in Figure C8ii, as more recent pipistrelle data suggests that trends from roost counts are negatively biased relative to those from field surveys; it is not at present possible to assess how much of the decline in Figure C8ii is genuine and how much might be an artefact caused by this bias.


Figure C8ii.  Historical declines in pipistrelle bat roost counts, 1977 to 1999.

Figure C8ii. Historical declines in pipistrelle bat roost counts, 1977 to 1999.


  1. The graph is a composite index of common pipistrelle, soprano pipistrelle, and unidentified pipistrelle roost count data from England.
  2. Graph shows unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).

Source: Bat Conservation Trust, using data collected by Stebbings and published in Harris et al. 1995, plus more recent data.


In response to the reported declines in bat populations, large-scale national monitoring was put in place through the establishment of the National Bat Monitoring Programme (NBMP) in the UK; the NBMP was established in 1996 with the first surveys undertaken in 1997.  It delivers trends for 11 of the UK’s 17 resident bat species, and since 1997 has deployed over 3,100 volunteers to record observations at almost 5,900 sites (Figure C8iii).


Figure C8iii.  Location of National Bat Monitoring Programme monitoring sites.

Figure C8iii. Location of National Bat Monitoring Programme monitoring sites.

The indicator has been compiled by the Bat Conservation Trust using data collected annually from the NBMP.  It is a composite index which combines population trend data for eight bat species.  Surveys for these species include visual and/or acoustic observations along predetermined transects within 1km randomly selected survey grids or along 1km sections of waterway, summer roost counts 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). 

For each species, Generalised Additive Modelling (GAM) is used to calculate the trends in numbers over time following Fewster et al. (2000).  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 eight 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 C8i).  A similar method was used to produce the smoothed trend for historical pipistrelle data (Figure C8ii).  The survey methods and statistical analysis used by the NBMP to produce individual species trends are described in Barlow et al. (2015).

Bats have benefited from strict legal protection, direct conservation action and public education (Mitchell-Jones 1993; Haysom et al. 2010), but remain vulnerable to pressures such as landscape change, climate change, development and emerging threats such as new building practices, wind turbines, and light pollution (Haysom et al. 2010; Kunz et al. 2007; Rebelo et al. 2009; Stone et al. 2009, 2012).  A significant increase in the lesser horseshoe bat population underpins the overall positive trend of the indicator since 1999 and has been attributed to conservation measures and a series of mainly mild winters that have enhanced winter survival.  The positive direction of the trend is in line with a prototype European indicator of trends in bat populations, developed from counts at hibernation sites in nine European countries including the UK (Haysom et al. 2014).


Table C8i.  Long-term and short-term percentage change in the species used in the bat indicator.


Long-term percentage
change (1999–2013)

Short-term percentage
change (2008–2013)


Eptesicus serotinus 



Habitats Directive
Annex IV

Daubenton’s bat
Myotis daubentonii



Habitats Directive
Annex IV 

Natterer’s bat
Myotis nattereri



Habitats Directive
Annex IV

Nyctalus noctula



Habitats Directive
Annex IV

common pipistrelle
Pipistrellus pipistrellus



Habitats Directive
Annex IV

soprano pipistrelle
Pipistrellus pygmaeus



Habitats Directive
Annex IV

brown long-eared bat
Plecotus auritus



Habitats Directive
Annex IV

lesser horseshoe bat
Rhinolophus hipposideros



Habitats Directive
Annexes II & IV

* Denotes a statistically significant change (based on smoothed data).

Note: To better capture patterns in the data, long-term and short-term assessments are made on the basis of smoothed data, with analysis of the underlying trend undertaken by Bat Conservation Trust.


In 2015-16, Defra commissioned a project (reference BE0112), to provide evidence statements to accompany a number of species trend indicators and an overview of the causes of biodiversity change. The output from this project is contained in a methods report, drivers of change report, and summary of evidence.  These are summarised indicator by indicator in a set of Evidence Statements, which aim to ensure that interpretation of trends, casual factors and relationship to policy interventions is rigorous, objective and reflects scientific consensus.

In parallel with the Evidence Statements, Defra also commissioned a Quality Assurance Panel to provide advice on improvements that could be considered to the species based indicators in the UK and England biodiversity indicator sets. The report of the review has led to an action plan of changes to be made as resources allow.


Further development planned

The indicator will be periodically re-evaluated in relation to the availability of suitable data.  Efforts to extend the NBMP survey network to deliver trends and indicators at country level are on-going.


Goals and targets

Aichi Targets for which this is a primary indicator

Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity.

Aichi icon 12Target 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.


Aichi Targets for which this is a relevant indicator

Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.

Aichi icon 5Target 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.

Aichi icon 11Target 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




Bat Conservation Trust

The National Bat Monitoring Programme



EUROBATS (The Agreement on the Conservation of Populations of European bats)


Joint Nature Conservation Committee

Tracking Mammals Partnership



European Environment Agency

European bat population trends – a prototype biodiversity indicator


Defra Evidence Statements project: Method report http://sciencesearch.defra.gov.uk/Document.aspx?Document=13933_BE0112FinalReport.pdf
Defra Evidence Statements project: Drivers of Change http://sciencesearch.defra.gov.uk/Document.aspx?Document=13945_Annex2_DriversOfChange.pdf
Defra Evidence Statements project: Summary of Evidence http://sciencesearch.defra.gov.uk/Document.aspx?Document=13947_Annex3_SummaryOfEvidence.pdf
Defra Quality Assurance Science Panel report View QASP report



Barlow, K.E., Briggs, P.A., Haysom, K.A., Hutson, A.M., Lechiara, N.L., Racey, P.A., Walsh, A.L. & Langton, S.D. (2015) Citizen science reveals trends in bat populations: the National Bat Monitoring Programme in Great Britain. Biological Conservation, 182, 14–26.

Fewster, R.M., Buckland, S.T., Siriwardena, G.M., Baillie, S.R. & Wilson, J.D. (2000) Analysis of population trends for farmland birds using generalized additive models. Ecology, 81, 1970–1984.

Guest, P., Jones, K.E. & Tovey, J. (2002)  Bats in Greater London: unique evidence of a decline over 15 years. British Wildlife, 13, 1–5.

Harris, S., Morris, P., Wray, S. & Yalden, D. (1995)  A review of British mammals: population estimates and conservation status of British mammals other than cetaceans. Peterborough, JNCC.

Haysom, K.A., Jones, G., Merrett, D. & Racey, P.A. (2010) Bats.  In: N. Maclean, ed. Silent Summer: The State of Wildlife in Britain and Ireland. Cambridge University Press, 259–280.

Haysom, K.A., Dekker, J., van der Meij, T. & van Strien, A. (2014) European bat population trends. A prototype biodiversity indicator. EEA Technical Report No. 19/2013. European Environment Agency, Luxembourg.

Jones, G., Jacobs, D.S., Kunz, T.H., Willig, M.R. & Racey, P.A. (2009) Carpe noctem: the importance of bats as bioindicators. Endangered Species Research, 8, 93–115.

Kunz, T.H., Arnett, E.B., Erickson, W.P., Hoar, A.R., Johnson, G.D., Larkin, R.P., Strickland, M.D., Thresher, R.W. & Tuttle, M.D. (2007) Ecological impacts of wind energy development on bats: questions, research needs, and hypotheses. Frontiers in Ecology and the Environment, 5, 315–324.

Mitchell-Jones, A.J. (1993) The growth and development of bat conservation in Britain. Mammal Review, 23, 139–148.

Racey, P.A. & Stebbings, R.E. (1972) Bats in Britain – a status report. Oryx, 11, 319–327.

Ransome, R.D. (1989)  Population changes of Greater horseshoe bats studied near Bristol over the past twenty-six years. Biological Journal of the Linnean Society, 38, 71–82.

Rebelo, H., Tarroso, P. & Jones, G. (2010) Predicted impact of climate change on European bats in relation to their biogeographic patterns. Global Change Biology, 16(2), 561–576.

Stebbings, R.E. (1988) Conservation of European Bats. London: Christopher Helm.

Stone, E.L., Jones, G. & Harris, S. (2009) Street lighting disturbs commuting bats. Current Biology, 19, 1123–1127.

Stone, E.L., Jones, G. & Harris, S. (2012) Conserving energy at a cost to biodiversity? Impacts of LED lighting on bats. Global Change Biology, 18, 2458–2465.


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Last updated: November 2016

Latest data available: 2014