C8. Mammals of the wider countryside (bats)

 

Type: State Indicator

 

Summary

Figure C8i.  Trends in bat populations, 1999 to 2013.

Figure C8i. Trends in bat populations, 1999 to 2013

Notes:

  1. The headline measure is a composite index of eight species: serotine, Daubenton's bat, Natterer’s bat, noctule, common pipistrelle, soprano pipistrelle, brown long-eared bat, and lesser horseshoe bat.
  2. Graph shows 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 period of the short-term or long-term assessment respectively, have shown a statistically significant increase or decrease.

Source: Bat Conservation Trust.

 

Assessment of change in widespread bat populations

 

Long term

Short term

Latest year

Bat populations

2010 indicator improving
1999–2012

2010 indicator stable
2007–2012

Increased (2013)

Note: Long-term and short-term assessments are made on the basis of smoothed trends to the penultimate year (2012) by the Bat Conservation Trust.  This is because the most recent smoothed data point (2013) is likely to change in next year’s update when additional data are included for 2014.  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 2012, bat populations have increased by 18 per cent; an assessment of the underlying smoothed trend shows this is a statistically significant increase. 
  • In the short term, between 2007 and 2012, an assessment of the underlying smoothed trend shows that bat populations have shown a small, insignificant decrease of less than 3 per cent, and are therefore considered to be stable. 
  • Four species (50 per cent) have increased in the long-term; one species, soprano pipistrelle, has decreased.  In the short term, between 2007 and 2012, seven of the eight species have shown no significant change in population size.  Lesser horseshoe bats have shown a statistically significant increase.
  • Bats have undergone severe declines historically.  Data from roost counts of pipistrelle bats show there was a 60 per cent decline from 1977 to 1999 in England; assessment of the underlying smoothed trend shows this was a significant decrease. 

 

Indicator description

The indicator shows changes in the population size of eight bat species, which occur in the wider countryside, based on summer field surveys and roost counts and winter hibernation counts.   Population change between 1999 and 2013 is analysed using a statistical model developed by the Bat Conservation Trust.  Bat populations have increased significantly in the long term.  The short-term assessment of the indicator, which considers change over the past five years (2007–2012), shows that the trend has stabilised over this period.  Assessments run to the penultimate year of the trend as the most recent smoothed data point (2013) is likely to change as future years of data are added.

The summer of 2013 was warmer and drier compared to the very poor season in 2012. Possibly as a result of this, most species showed a slight recovery from the dip in 2012.

 

Relevance

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).

 

Background

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 pipistrells bat roost counts, 1977 to 1999.

Notes:

  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 by deploying a network of over 3,500 volunteers to record observations at over 5,900 sites (Figure C8iii). 

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).  A paper documenting the survey methods and statistical analysis used by the NBMP to produce individual species trends is currently under review for publication (Barlow et al. In review).

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 recently published prototype European indicator of trends in bat populations, developed from counts at hibernation sites in nine European countries including UK (Haysom et al. 2014).

 

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

Species

Long-term percentage
change (1999–2012)

Short-term percentage
change (2007–2012)

Status

serotine
Eptesicus serotinus 

-4.3

-3.5

 Habitats Directive
 Annex IV

Daubenton’s bat
Myotis daubentonii

11.7*

2.1

 Habitats Directive
 Annex IV 

Natterer’s bat
Myotis nattereri

20.9*
(2002–2012)

4.8

Habitats Directive
Annex IV

noctule
Nyctalus noctula

15.9

-9.4

Habitats Directive
Annex IV

common pipistrelle
Pipistrellus pipistrellus

64.7*

1.3

Habitats Directive
Annex IV

soprano pipistrelle
Pipistrellus pygmaeus

-17.5*

-8.1

Habitats Directive
Annex IV

brown long-eared bat
Plecotus auritus

14.7
(2001–2012)

0.4

Habitats Directive
Annex IV

lesser horseshoe bat
Rhinolophus hipposideros

76.8*

18.5*

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.

 

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

Figure C8iii. Location of National Bat Monitoring Programme

 

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

None

 

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.

Aichi icon 7Target 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.

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.

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 icon 13Target 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 diversity.

Strategic Goal D. Enhance the benefits to all from biodiversity and ecosystems.

Aichi icon 14Target 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 and vulnerable.

Aichi icon 15Target 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.

 

Web links for further information

Reference

Title

Website

Bat Conservation Trust

The National Bat Monitoring Programme

http://www.bats.org.uk/pages/nbmp.html

EUROBATS

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

http://www.eurobats.org/

Joint Nature Conservation Committee

Tracking Mammals Partnership

http://www.jncc.defra.gov.uk/page-1741

 

European Environment Agency

European bat population trends – a prototype biodiversity indicator

http://www.eea.europa.eu/publications/european-bat-population-trends-2013

 

References

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

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.  pp 259–280 in: Maclean, N. (ed.) Silent Summer: The State of Wildlife in Britain and Ireland.  Cambridge University Press.

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. and 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: December 2014

Latest data available: 2013