Species Population Trends

Summary of Trends

Positive trends: 

In 2011, five species showed statistically significant increases in at least one survey. Significant positive trends were reported for the following species:

1. Greater horseshoe bat (Colony Count)
2. Lesser horseshoe bat (Hibernation Survey & Colony Count)
3. Natterer’s bat (Hibernation Survey)
4. Whiskered/Brandt's bat (Hibernation Survey)
5. Common pipistrelle (Field Survey) 

From these results we conclude that the lesser horseshoe bat population is increasing as both sources of data are indicating the same trend. We also conclude that the common pipistrelle population is increasing, as Field Survey data are considered to be more reliable than Colony Count data for this species. It is less clear whether the increasing trend seen in Natterer’s bat from the Hibernation survey is a real reflection of population increase or other factors as the Colony Count data do not support the increase. The significant increase recorded for whiskered/Brandt's bat this year should be treated with caution as this trend comprises data from more than one species and is less likely to be reliable. The greater horseshoe bat trend should also be treated with some caution. This is mainly due to the relatively small sample size and short duration of use of consistent survey protocol in the Colony Count for this species, and the trend is not supported with a similar result from the Hibernation Survey.

Negative trends: 

Significant negative trends were reported for common pipistrelle and soprano pipistrelle in 2011 (Colony Counts), though these negative trends may be highly influenced by the mobility of these species. The Field Survey showed a significant increase for common pipistrelle and a stable trend for soprano pipistrelle in 2011 and these Field Survey trends are presently considered more robust than the Colony Count trends.

Stable species: 

The remaining species: Daubenton’s bat, brown long-eared bat, soprano pipistrelle, noctule and serotine all showed no significant trends in 2011.

Daubenton’s bat has shown a fairly stable trend from both Hibernation and Waterway Survey data, although there has been a slight, but not significant decline since 2005. Brown long-eared bat had shown a slight increase since 2005, but lower counts in 2008 and 2009 have resulted in no overall significant trend from either the Hibernation Survey or Colony Count. Soprano pipistrelle showed a borderline significant increase in the Field Survey in 2010 but this has not been sustained into 2011. Noctule had also started to show an increase due to very high counts in 2008 but counts have returned to previous levels and the overall trend is not significant. No significant trend has been shown for serotine from either the Field Survey or Colony Counts. Sample sizes are small and confidence intervals large for this species, however, as it is encountered infrequently and has a restricted range in the UK, and it may be difficult to detect trends.

Trends in context: 

The 2011 results show that currently all species surveyed appear to be stable or increasing based on data from at least one survey. Whilst these are positive results, it should also be taken into account that these trends reflect what has happened to bat populations since the late 1990s. It is generally considered that prior to this in the period between the 1950s and the late 1980s /early 1990s there were significant historical declines in bat populations, although evidence is fragmented and few data were collected in a systematic way (e.g. Harris et al. 1995; Stebbings 1988). 

Other species: 

For the remaining UK bat species (Bechstein's bat, Alcathoe bat, Leisler's bat, Nathusius' pipistrelle, barbastelle, grey long-eared bat and greater mouse-eared bat) there are insufficient data available at present to allow calculation of population trends. More details can be found here.

Species summaries:

The table below shows a summary of the UK bat species trends derived from NBMP survey results to the end of 2011. For each species, the number of sites contributing to the 2011 trend calculations is shown as well as an approximation of the average annual percentage change since the baseline year. It should be noted, however, that the average annual percentage change makes assumptions about the data analysis, and is only genuinely appropriate for those species for which the trend line appears to be linear.

Click on each species name for more details.

UK bat species population trends summary table

 Notes: Bold indicates significant result at 5% (P* indicates most statistically robust trend. # indicates UK Biodiversity Action Plan priority species

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.

Stebbings, R.E. (1988). Conservation of European Bats. London, Christopher Helm.

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