1c. Trends in populations of selected species (bats)

Focal Area: Status and trends in the components of biological diversity. 

Type: State Indicator

 

Summary

Figure 1c (i).  Trends in widespread bat populations, 1999 to 2010

Figure 1c(i) Trends in widespread bat populations, 1999 to 2010

 

Assessment of change in widespread bat populations

 

Long term

Since 2000

Latest year

Bat populations

indicator declining 1978-1992

 indicator improving

Increased (2010)

 

 

  • 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 20 per cent.

Indicator description

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.  Populations of these bat species have been relatively stable during the last decade, with the overall trend positive. Assessment is based on the analysis of these trends, using a statistical model. Since 2000, the populations have increased by 20 per cent, giving an ‘improving’ assessment.
 
Bats experienced major declines during the latter half of the twentieth 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, with more recent contributions to the positive trend to a lesser extent from other species such as noctule (Nyctalus noctula) and common pipistrelle (Pipistrellus pipistrellus).

 

Relevance

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 entirely on insects and other arthropods. In order to thrive they require adequate roosting (particularly breeding and hibernating) opportunities, 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.
 
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

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 2,200 volunteers to record observations at approximately 4,700 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 1c (iii).
 
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 1 (ii)).

 

Table 1c.  Species used in the bat indicator

Species

Status

Eptesicus serotinus (serotine)

 

Habitats Directive Annex IV

Myotis daubentonii (Daubenton’s bat)

Habitats Directive Annex IV

 

Nyctalus noctula (noctule)

 

Habitats Directive Annex IV. UK BAP species from 2007

Pipistrellus pipistrellus (common pipistrelle)

 

Habitats Directive Annex IV. UK BAP species until 2007

Pipistrellus pygmaeus (soprano pipistrelle)

 

Habitats Directive Annex IV. UK BAP species

Rhinolophus hipposideros (lesser horseshoe bat)

Habitats Directive Annexes II & IV. UK BAP species

 

 

 

Figure 1c(ii).  Generalised Additive Modelling trend in bat populations, 1999 to 2010

 

Figure 1c(ii) Generalised Additive Modelling trend in bat populations, 1999-2010

 

Figure 1c (iii). Location of monitoring sites for the 6 index species

 

Figure 1c(iii) Location of monitoring sites for the 6 index species

 

Further development planned

A method to derive population trends for bats in woodland, farmland and urban landscapes has been trialed. Efforts to extend the survey network to deliver trends at country level are ongoing.

Current assessment of the indicator is based on the analysis of trends, using a statistical model which may be subject to further development.

 

Web links for further information

Reference

Title

Web site

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/index.htm

Joint Nature Conservation Committee

Tracking Mammals Partnership

http://www.jncc.defra.gov.uk/page-1757

 

 

 

 

Download Datasheet 

 

Last updated:  May 2011

Latest data available: 2010

 

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