C8. Mammals of the wider countryside (bats)

 

Type: State Indicator

Summary

Figure C8i.  Trends in bat populations, 1999 to 2012.

Figure C8i. Trends in bat populations, 1999 to 2012.

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. Darker line shows unsmoothed data, paler line shows smoothed trend data.

Source: Bat Conservation Trust.

 

Figure C8ii.  Historical declines in pipistrelle bat roost counts.

Figure C8ii. Historical declines in pipistrelle bat roost counts.

Notes:

  1. The graph is a composite index of common pipistrelle, soprano pipistrelle, and unidentified pipistrelle roost count data.
  2. Darker line shows unsmoothed data, paler line shows smoothed trend data.

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

 

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

Decreased (2012)

Historical pipistrelle bat roost counts

indicator declining
1977–1999

Not assessed

Not assessed

 

  • 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.
  • Since 1999, when trends from standardised large-scale monitoring became available through the National Bat Monitoring Programme, bat populations have increased by 18 per cent (Figure C8i).  The most recent five year assessment shows a decrease of slightly less than three per cent in the index, giving a stable short-term assessment. 
  • Bats have undergone severe declines historically (Figure C8ii).  Data from colony counts of pipistrelle bats show a 59 per cent decline from 1977 to 1999. 

 

 

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.  Two additional species trends, Natterer’s bat (Myotis nattereri) and brown long-eared bat (Plecotus auritus), have been incorporated into the indicator for the first time this year.  The addition of these species improves the representation of species associated with woodland habitats in the indicator.  Both species occur throughout the UK, and their inclusion also therefore broadens the geographical coverage of species.  Population change between 1999 and 2012 is analysed using a statistical model developed by the Bat Conservation Trust (Figure C8iii).  A paper documenting the statistical analysis is in preparation.  Since 1999 bat populations have increased significantly.  The short-term assessment of the indicator, however, which considers change over the past five years, shows that there has been a decrease of slightly less than three per cent since 2007, giving a stable assessment.

 

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 during the period thought to have seen 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.  Figure C8ii was replaced in 2013 as new analysis of historical declines in pipistrelle colony count data allowed the graph previously shown (from Harris et al, 1995) to be redrawn and confidence intervals calculated.  The base point of the new graph is set to 100 in 1999 as sample sizes are small in the first few years of the series.  The bats in the dataset for Figure C8ii pre-date the period in which separate common (Pipistrellus pipistrellus) and soprano pipistrelle (Pipistrellus pygmaeus) species had been identified, and the proportion of each species is unknown in the historical data.  The analysis uses only sites with five or more years of 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.

 

In response to these declines, large-scale national monitoring was put in place through the establishment of the National Bat Monitoring Programme (NBMP) so that future changes could be detected; the NBMP was established in 1996 with the first surveys undertaken in 1997.  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 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 lesser horseshoe bat increase has been sustained throughout the period of the indicator.  The recent dip in the indicator is largely due to a drop in encounter rates of common pipistrelles, soprano pipistrelles and noctules (Nyctalus noctula) in the field survey data in 2011 and 2012.

 

References

Guest, P., Jones, K.E. and 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. and 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. and 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.

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.

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

 

Relevance

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.

 

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 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 availability. 

 

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 3,500 volunteers to record observations at over 5,600 sites.

 

The indicator is a composite index which combines population trend data for eight bat species.  Surveys for these species include summer roost 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 eight index species are shown in Figure C8v.

 

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 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 C8iii).  A similar method was used to produce the smoothed trend for historical pipistrelle data; Figure C8iv shows the  smoothed historical data, as presented in figure C8ii, with confidence intervals.

 

Table C8i.  Species used in the bat indicator.

Species Status

serotine (Eptesicus serotinus)

Habitats Directive Annex IV

Daubenton's bat (Myotis daubentonii)

Habitats Directive Annex IV

Natterer's bat (Myotis nattereri)

Habitats Directive Annex IV

noctule (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

 

 

Figure C8iii.  Generalised Additive Modelling trend in bat populations, 1999 to 2012.

Figure C8iii. Generalised Additive Modelling trend in bat populations, 1999 to 2012.

Notes: 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.  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 2012 is significantly larger than in 1999.

Source: Bat Conservation Trust.

 

 

Figure C8iv. Generalised Additive Modelling trend in pipistrelle bat roost counts, 1977 to 1999.

Figure C8iv. Generalised Additive Modelling trend in pipistrelle bat roost counts, 1997 to 1999

Notes: The graph is a composite index of common pipistrelle, soprano pipistrelle, and unidentified pipistrelle roost count data.

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

 

 

Figure C8v.  Location of monitoring sites.

Figure C8V. Location of monitoring sites

 

 

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 individual national species trends.  It is planned to expand the European indicator to include 15 or more countries in the near future.

 

Further development planned

The indicator has been refined this year, so that the indicator represents a wider range of species.  It will be periodically re-evaluated in relation to the availability of suitable data.  Efforts to extend the 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-1757

 

 

Download Datasheet

 

Last updated: October 2013

Latest data available: 2012 (Bat populations); 1999 (Historical pipistrelle bat roost counts)