Species Population Trends

Summary of Trends

Positive trends: 

In 2010, 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. Common pipistrelle (Field Survey)
5. Soprano pipistrelle (Field Survey)

From these results we conclude that the lesser horseshoe 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 generally than Colony Count data. 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. Similarly the increase recorded for soprano pipistrelle in the Field Survey has reached borderline significance in 2010 while the Colony Counts indicate a decline. The greater horseshoe bat trend should be treated with caution at present mainly due to the relatively small sample size and short duration of use of consistent survey protocol for this species.

Negative trends: 

Significant negative trends were reported for common pipistrelle and soprano pipistrelle in 2010 (Colony Counts), though these negative trends may be highly influenced by the mobility of these species. The Field Survey showed a significant increase for both species and these Field Survey trends are presently considered more robust than the Colony Count trends.

Stable species: 

The remaining species: Daubenton’s bat, whiskered/Brandt's bat, brown long-eared bat, noctule and serotine all showed no significant trends in 2010.

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. Whiskered/Brand's bat has shown an increase in recent years but this has not continued and there is no significant trend; this trend should be treated with extreme caution as it combines data from more than one species and is likely to less reliable. 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. Noctule had also started to show an increase due to very high counts in 2008 but these high values 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 2010 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 2010. For each species, the number of sites contributing to the trend 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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