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Brown long-eared bat trends for Great Britain

Plecotus auritus

Species factsheetDistribution and abundance

GB-level populations trends for brown long-eared bat from the Hibernation Survey and the Roost Count are shown on this page.

Population trends for brown long-eared bat are also produced at country-level for England and Wales. There are insufficient data available to calculate a population trend for this species in Scotland.


Hibernation Survey

GB index of brown long-eared bat population from Hibernation Surveys

Brown long-eared bat hibernation survey trend GB

Note: The graph above shows the unsmoothed index value for each year (green crosses), the smoothed trend (solid line) and 95% confidence intervals (dotted lines). The smoothed trend for 2016 is shown as a dashed line to indicate that it is provisional.

The smoothed index is currently 31.3% below the 1999 base year value, equivalent to an annual decrease of 2.2%. The smoothed index has been below the baseline year since 1999, however this decline has only become significant in the current year, and by a very narrow margin. Overall there has been a significant decline in the smoothed index since 1999. Differences between trends for England and Wales are not significant.

From all years for which data are available (1990-2016), counts from 427 sites contribute to the trend (sites surveyed in two or more years with brown long-eared bat recorded in at least one year).


Roost Count 

GB index of brown long-eared bat population from Roost Counts

Brown long-eared bat roost count trend GB

Note: The graph above shows the unsmoothed index value for each year (green crosses), the smoothed trend (solid line) and 95% confidence intervals (dotted lines). The smoothed trend for 2016 is shown as a dashed line to indicate that it is provisional.

The smoothed index is currently 20.1% above the base year value, equivalent to an annual increase of 1.2%. The trend has fluctuated since the start of monitoring. Since 2004 the smoothed index has been above the baseline year however at no point has it differed significantly from the baseline year. Overall there has been no significant change in the smoothed index since the baseline year. Differences between trends for England and Wales are not significant.

Data from 158 sites surveyed between 1990 and 2016 contribute to the trend (sites surveyed in at least two years).

Note: the baseline year for calculation of this trend has been set at 2001 as very few roosts were counted in earlier years.


Summary of survey results

The trend from the Roost Count shows no significant change in the smoothed index since the baseline year, while the Hibernation Survey trend shows a significant decline in the smoothed index in the most recent year when compared to the baseline year. The margin by which the Hibernation Survey trend is significant is small (the upper CI of the smoothed trend in 2016 is 99.2 compared to a baseline year index value of 100), and the estimate of the smoothed index value for the most recent year is considered provisional until confirmed by further years of monitoring (see Population Trend Analysis). Given the provisional nature of the estimate for the most recent year, the small margin of significance and the fact that this margin is highly likely to change when additional years of monitoring data are added to the trend, there is not yet sufficient certainty in the trend to alter the previous assessment of population change. Therefore the population of brown long-eared bat in Great Britain is currently considered to have been stable since 1999, however this assessment will need to be reviewed and potentially revised in light of the results from the next year of monitoring.

 


Distribution and abundance

The brown long-eared bat is relatively common and widespread throughout the UK with the exception of exposed islands with little woodland such as Orkney, Shetland and the Outer Hebrides. It is also recorded in the Channel Islands.

Population estimate

The population estimates are considered to be poor and should be treated with caution. Estimates are based on limited population data and are extrapolated from surveys of only part of the population

Country

UK

England

Wales

Scotland

N.Ireland

Number

245,000

155,000

17,500

27,500

45,000

 Source

 

 Harris et al. 1995

 Harris et al. 1995

 Harris et al. 1995

Russ 1999 


 

References

Harris S., Morris, P., Wray, S. & Yalden, D. (1995) A review of British mammals: population estimates and conservation status of British mammals other than cetaceans. JNCC, Peterborough.

Russ, J.M. 1999. The Microchiroptera of Northern Ireland: community composition, habitat associations and ultrasound. Unpublished PhD thesis. Queen’s University, Belfast.


Return to:

Top of pageSpecies population trendsReport HomeContents page

 

 

Brown long-eared bat factsheet

 

Listen to how a brown long-eared bat sounds on a bat detector 

 

 

Current distribution of brown long-eared bat in the UK

(Map taken from 3rd Report under Article 17 on implementation of the Habitats Directive in the UK, JNCC 2013)

Brown long-eared bat distribution

 

 

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