C8. Mammals of the wider countryside (bats)

Summary

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 pipistrelle.

Source: Bat Conservation Trust.

 

 

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. Peterborough, JNCC.

 

Assessment of change in widespread bat populations

	Long term	Since 2000	Latest year
Bat populations	1978–1992		Decreased (2011)

• 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.

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.  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.

Relevance

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 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 C8ii).

Table C8i.  Species used in the bat indicator.

Figure C8ii.  Generalised Additive Modelling trend in bat populations, 1999 to 2011.

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 ongoing.

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.

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 diversity.

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 diversity.

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 and vulnerable.

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.

Web links for further information