C8. Mammals of the wider countryside (bats)


Type: State Indicator


Indicator Description

Bat species make up a third of the UK’s mammal fauna and occur in most lowland habitats across the UK.  The indicator shows changes in the population size of eight widespread bat species, based on summer field surveys and roost counts and winter hibernation counts.  Population change between 1999 and 2017 is analysed using a statistical model developed by the Bat Conservation Trust. 




The bat index has increased by 31% between 1999 and 2016. In the short term, between 2011 and 2016, the bat index has increased by 4.7%.

The bat index is a composite of eight species trends. Since 1999 populations of four of the bat species included in the index have increased and four have shown no significant change. 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 significant increases in the populations of two species, lesser horseshoe bat and common pipistrelle.


Figure C8i.  Trends in bat populations, 1999 to 2017.






  1. The headline measure is a composite index of eight bat species: brown long-eared bat, common pipistrelle, Daubenton's bat, lesser horseshoe bat, Natterer’s bat, noctule, serotine and soprano pipistrelle.
  2. The model used to analyse some individual species trends has changed since the previous publication, and these results are therefore not directly comparable (see Background section for more details).
  3.  The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line) with its 95% confidence interval (shaded).
  4. The bar chart shows the percentage of species which, over the time periods of the long-term and short-term assessments, have shown a statistically significant increase or decline, or no significant change.

Source: Bat Conservation Trust.

Four species have increased over the period of the long-term assessment: common pipistrelle, Daubenton’s bat, lesser horseshoe bat and Natterer’s bat.   Four species have shown no significant long term change in population size: brown long-eared bat, noctule, soprano pipistrelle and serotine.  In the short term, between 2011 and 2016, three species continue to show an increase: common pipistrelle, Daubenton’s bat and lesser horseshoe bat.  Five species, brown long-eared bat, Natterer’s bat, noctule, serotine and soprano pipistrelle, have shown no significant short term change.  No species show a decline in either the long- or short-term.

Long and short term assessments are run to the penultimate year of the trend as the most recent smoothed data point (2017) is likely to change as future years of data are added.  The assessment of change in the latest year (2017) is based on unsmoothed data.


Assessment of change in widespread bat populations


Long term

Short term

Latest year

Bat populations



Increased (2017)

Note: Long-term and short-term assessments are made on the basis of smoothed trends to the penultimate year (2016) by the Bat Conservation Trust.  This is because the most recent smoothed data point (2017) is likely to change in next year’s update when additional data are included for 2018. As such, the latest year assessment is based on unsmoothed data.


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Download Datasheet

Download Technical background document

Download Evidence statement


Last updated: July 2018

Latest data available: 2017 (2016 smoothed)

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