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C8. Mammals of the wider countryside (bats)

Type: State Indicator

This indicator was updated in 2023.

Introduction

This indicator shows changes in the relative abundance of 11 of the UK’s 17 breeding bat species, based on data from transect surveys, roost counts and counts at hibernation sites. Whilst 11 species are included there are only 10 trends, as an aggregate trend is used for the whiskered bat (Myotis mystacinus) and Brandt’s bat (Myotis brandtii); these two species are difficult to distinguish between in the field. Bat species make up a third of the UK’s mammal fauna and occur in most lowland habitats across the UK.

Key results

The smoothed bat index has increased by 49% between 1999 and 2020. In the short term, between 2015 and 2020, the bat index has increased by 6% (Figure C8i).

The bat index is a composite of 10 trends (including 11 species, two of which are combined in a single trend). Since 1999, 5 of the trends included in the index have increased and 5 have shown little or no change (Figure C8ii). The UK’s rarer and more specialised bat species are not included in the index due to difficulties monitoring these species.

The increase in the index is underpinned by large statistically significant increases in populations of three species, greater horseshoe bat, lesser horseshoe bat and common pipistrelle. These increases indicate that some bat species are starting to recover after what are believed to have been major population declines during the 20th century.

Figure C8i is a line graph showing how the index for bats in the UK has changed between 1999 to 2022. The index has increased by around 50% between 1999 and 2022

Notes about Figure C8i:

  1. Figure C8i shows the unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
  2. This indicator includes 10 trends covering 11 species of bats, as an aggregate trend is used for whiskered bat (Myotis mystacinus) and Brandt’s bat (Myotis brandtii); these two species have been combined due to difficulties distinguishing between them in the field.
  3. Since 2018, this indicator has been extended to include 11 species instead of eight. The complete time-series in the accompanying dataset was also updated to reflect these changes.

Source: Bat Conservation Trust.

Figure C8ii consists of two 100% stacked bar charts showing the percentage of individual species within the UK bat index that have increased, decreased or shown little change over both the long term (since 1999) and short term (2015 to 2020)

Notes about Figure C8ii:

  1. Figure C8ii shows the percentage of species group trends which, over the time periods of the long-term and short-term assessments, have shown a statistically significant increase or decline, or little change.
  2. Since 2018, this indicator has been extended to include 11 species instead of eight. The complete time-series in the accompanying dataset was also updated to reflect these changes.

Source: Bat Conservation Trust.

The smoothed bat index increased every year between the 1999 baseline and 2009, it was relatively stable between 2009 and 2013, before increasing again between 2013 and 2019. Since 2019 the index has once again been relatively stable. The composite indicator masks variation between the species that contribute to it. The long-term increase in the indicator is primarily driven by strong increases in three species; greater horseshoe bat, lesser horseshoe bat and common pipistrelle. Between 1999 and 2020, the combined survey trend for these species increased by 210%, 119% and 89% respectively. Two other species showed weaker increases over the same period, and the remaining 5 species groups showed little change.

In the short term, between 2015 and 2020, 2 species have increased significantly and the remaining species groups show no significant short-term change. No species show a decline in either the long or short term, however it is not possible to produce separate trends for whiskered bat and Brandt’s bat, as they cannot be reliably distinguished between in the field. It is therefore possible that an increase in one species could mask a decline in the other. It is also important to note that the UK’s rarer and more specialised bat species are not included in the index due to difficulties monitoring these species.

Assessment of change in widespread bat populations

  Long term Short term Latest year
Bat populations

Improving

1999–2020

Improving

2015–2020

No change

(2020 to 2022)

Notes for Assessment of Change table:

Long-term and short-term assessments are made on the basis of smoothed trends to the penultimate year (2022) by the data providers. Due to the COVID-19 pandemic, National Bat Monitoring Programme Hibernation Surveys were suspended during the winter of 2020 to 2021. As a result, the 2021 index value has been estimated using imputed Hibernation Survey data for that year. The assessment of long and short-term change would usually be based on smoothed trends to the penultimate year, which in this case would be 2021. This is because the most recent smoothed data point (2022) is likely to change in next year’s update when additional data are included for 2023. However, due to the reliance of the 2021 index value on imputed data, the assessments of change here are instead based on the penultimate year for which full data is available, which is 2020. The latest year change is assessed between 2020 and 2022 and is based on unsmoothed values. Nevertheless estimates make use of all data up to and including 2022.

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Relevance

Bat populations 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 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).

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Background

The species used in this index (Table C8i) occur 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, which assist them in commuting between roost sites and feeding locations.

Key pressures on bats, including landscape change, agricultural intensification, development and habitat fragmentation, are also relevant to many other wildlife groups. Bats are believed to have experienced major declines throughout Western Europe during the 20th century, which have been attributed to persecution, agricultural intensification, habitat and roost loss, remedial timber treatment and declines of their insect prey. Evidence of these declines (synthesised in Haysom et al. 2010) is fragmented as during this period few data were collected in a systematic way. Evidence includes:

  • Well documented range contractions of greater horseshoe bat and lesser horseshoe bat across Great Britain and Europe.
  • Reports of the loss of large colonies of several species from traditional roosting sites.
  • Reductions in the number of known maternity colonies across Great Britain.
  • A small number of published population trends (for example, Ransome, 1989; Guest et al. 2002).

The bat index and long-term assessment reflect changes in bat populations since 1999 and indicate that more recently some UK bat populations are beginning to recover. This recovery 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). The greatest weight of evidence suggests two factors have had a positive impact on bat populations in the UK; a reduction in human disturbance since the introduction of strict legal protection, and a milder climate (Burns et al. 2016). Climate changes over winter and spring have been shown to benefit horseshoe bat species (Battersby, 2005; Froidevaux et al. 2017; Schofield, 2008). The impact of climate change on other UK bat species is less clear. Bats have also benefited from 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, wind turbines, and light pollution (Browning et al. 2021; Haysom et al. 2010; Kunz et al. 2007; Rebelo et al. 2010; Stone et al. 2009, 2012).

The National Bat Monitoring Programme was established in 1996, with the first surveys undertaken in 1997. It currently delivers population trends for 11 of the UK’s 17 breeding bat species (two of which are combined) and has deployed 4,152 volunteers to record bat population data at 7,030 sites (see Figure C8iii).

In 2018 this indicator was extended from 8 species to 11 bat species. Data were updated for the entire time series to include all 11 bat species.

Figure C8iii. Location of National Bat Monitoring Programme monitoring sites

ukbi-2023-c8iii.png

This indicator shows changes in the relative abundance of 11 of the UK’s 17 breeding bat species: brown long-eared bat, common pipistrelle, Daubenton's bat, greater horseshoe bat, lesser horseshoe bat, Natterer’s bat, noctule, serotine, soprano pipistrelle and whiskered/Brandt’s bat (the latter two species cannot be distinguished between during monitoring surveys and so are treated as one species group). It is compiled by the Bat Conservation Trust using data collected annually from the National Bat Monitoring Programme (NBMP). Surveys for these species include summer roost counts, counts at hibernation sites and visual and/or acoustic observations made along predetermined transects. Most species are surveyed by two different survey methods, both of which are included in the index apart from summer roost count data for common and soprano pipistrelle. Pipistrelle species’ frequent ‘roost switching’ causes a negative bias in trends calculated from summer roost counts, so these data are omitted (Dambly et al. 2021).

For each species, Generalised Additive Modelling (GAM) is used to calculate the trends in numbers over time (Fewster et al. 2000). The models include terms for factors that can influence the apparent population averages (for example, bat detector model, temperature, and so on), so their effect can be taken into account. The GAM models produce smoothed trends which are more robust against random variation between years. 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 data from earlier years. As such, indices published in previous years are not strictly comparable to the current index. To generate the composite bat indicator and confidence intervals, each species has been given equal weighting, and the annual index figure is the geometric mean in that year (Figure C8i). Confidence intervals are relatively wide due to the high variability inherent in bat monitoring data and the rarity of several species. Long- and short-term assessments are run to the penultimate year of the trend as the most recent year’s smoothed data point is likely to change as future years of data are added. The latest year change is based on unsmoothed data. The survey methods and statistical analysis used by the NBMP to produce individual species trends are described in Barlow et al. (2015).

Species group Short-term time frame Short-term change Short-term significance of change Long-term time frame Long-term change Long-term significance of change
serotine (Eptesicus serotinus) 2015 to 2020 10.7 Little change 1999 to 2020 0.9 Little change
Daubenton's bat (Myotis daubentonii) 2015 to 2020 -6.2 Little change 1999 to 2020 11.1 Little change
Natterer's bat (Myotis nattereri) 2015 to 2020 3.0 Little change 2002 to 2020 34.8 Increase
whiskered Brandt’s bat (Myotis mystacinus brandti) 2015 to 2020 -2.3 Little change 1999 to 2020 22.4 Little change
noctule (Nyctalus noctula) 2015 to 2020 15.8 Little change 1999 to 2020 37.6 Little change
common pipistrelle (Pipistrellus pipistrellus) 2015 to 2020 5.4 Little change 1999 to 2020 88.6 Increase
soprano pipistrelle (Pipistrellus pygmaeus) 2015 to 2020 15.8 Little change 1999 to 2020 42.9 Increase
brown long-eared bat (Plecotus auritus) 2015 to 2020 -5.5 Little change 2001 to 2020 -2.1 Little change
lesser horseshoe bat (Rhinolophus hipposideros) 2015 to 2020 10.2 Increase 1999 to 2020 118.9 Increase
greater horseshoe bat (Rhinolophus ferrumequinum) 2015 to 2020 21.3 Increase 1999 to 2020 210.0 Increase

Notes about Table C8i:

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. All 11 species are protected through Annex IV of the Habitats Directive. Greater horseshoe bat and lesser horseshoe bat are also listed on Annex II of the Directive – leading to Special Areas of Conservation being designated for these species.

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Goals and Targets

The UK and England Biodiversity Indicators are currently being assessed alongside the Environment Improvement Plan Targets, and the new Kunming-Montreal Global Biodiversity Framework Targets, when this work has been completed the references to Biodiversity 2020 and the Aichi Global Biodiversity Framework Targets will be updated.

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.

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.

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.

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.

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References

  • Barlow, K. E., Briggs, P. A., Haysom, K. A., Hutson, A. M., Lechiara, N. L., Racey, P. A., Walsh, A. L. and Langton, S. D. (2015). Citizen science reveals trends in bat populations: the National Bat Monitoring Programme in Great Britain. Biological Conservation, 182, pp. 14 to 26.
  • Battersby, J. (2005). UK Mammals: Species Status and Population Trends. First Report by the Tracking Mammals Partnership. Peterborough, UK.
  • Browning, E., Barlow, K.E., Burns, F., Hawkins, C., Boughey, K. (2021), Drivers of European bat population change: a review reveals evidence gaps. Mammal Review, 51, pp. 353 to 368.
  • Burns F, Eaton M. A., Barlow K. E., Beckmann B. C., Brereton T., Brooks D. R., Brown P. M. J., Al Fulaij A., Gent T., Henderson I., Noble D. G., Parsons M., Powney G. D., Gregory R. D. (2016) Agricultural Management and Climatic Change Are the Major Drivers of Biodiversity Change in the UK. PLoS ONE 11(3): e0151595. https://doi.org/10.1371/journal.pone.0151595.
  • Dambly, L.I., Jones, K.E., Boughey, K.L., Isaac, N.J.B. (2021). Observer retention, site selection and population dynamics interact to bias abundance trends in bats. Journal of Applied Ecology, 58, pp. 236 to 247.
  • Fewster, R. M., Buckland, S. T., Siriwardena, G. M., Baillie, S. R. and Wilson, J. D. (2000). Analysis of population trends for farmland birds using generalized additive models. Ecology, 81, pp. 1970 to 1984.
  • Froidevaux J. S. P., Boughey K. L., Barlow K. E., Jones G. (2017). Factors driving population recovery of the greater horseshoe bat (Rhinolophus ferrumequinum) in the UK: implications for conservation. Biodiversity and Conservation, 26, pp. 1 to 21.
  • Guest, P., Jones, K. E. and Tovey, J. (2002). Bats in Greater London: unique evidence of a decline over 15 years. British Wildlife, 13, pp. 1 to 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 to 280 in: Maclean N (ed.) Silent Summer: The State of Wildlife in Britain and Ireland. Cambridge University Press.
  • Kunz, T. H., Arnett, E. B., Erickson, W. P., Hoar, A. R., Johnson, G. D., Larkin, R. P., Strickland, M. D., Thresher, R. W. and Tuttle, M. D. (2007). Ecological impacts of wind energy development on bats: questions, research needs, and hypotheses. Frontiers in Ecology and the Environment, 5, pp. 315 to 324.
  • Mitchell-Jones, A. J. (1993). The growth and development of bat conservation in Britain. Mammal Review, 23, pp. 139 to 148
  • 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 to 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 to 576.
  • Schofield, H. (2008). The Lesser Horseshoe Bat Conservation Handbook. Vincent Wildlife Trust, Herefordshire.
  • Stone, E.L., Jones, G. & Harris, S. (2009). Street lighting disturbs commuting bats. Current Biology, 19, 1123 to 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 to 2465.

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Downloads

Download the Datasheet and Technical background document from JNCC's Resource Hub.

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Last updated: November 2023

Latest data available: 2022

 

This content is available on request as a pdf in non-accessible format. If you wish for a copy please go to the enquiries page.

 

Categories:

UK Biodiversity Indicators 2023

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