Summary of findings
This report covers the findings of the National Bat Monitoring Programme (NBMP) in 2011. The primary aim of the programme is to produce statistically-defensible population trend data for UK bat species.
The core monitoring techniques employed by the programme are the Field, Waterway, and Hibernation Surveys and summer maternity Colony Counts. Newer monitoring techniques involve the use of broadband bat detectors to record a range of species along woodland transects (Woodland Survey for barbastelles) and around lakes (Nathusius’ pipistrelle pilot survey). The total NBMP site network now stands at 5,330. In 2011 a total of 2024 sites were monitored by 1135 dedicated NBMP volunteers. For the core surveys, 89% of these were repeat sites, compared to 83% repeat sites in 2010.
At present sufficient data are collected by the programme to produce population trends for 11 of the UK’s 17 resident bat species.
In 2011, five species showed statistically significant increases in at least one survey. Significant positive trends were reported for the following species:
Greater horseshoe bat (Colony Count)
Lesser horseshoe bat (Hibernation Survey & Colony Count)
Natterer’s bat (Hibernation Survey)
Whiskered/Brandt's bat (Hibernation Survey)
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.
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 both species and these Field Survey trends are presently considered more robust than the Colony Count trends.
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 started to show an increase due to very high counts in 2008 but counts have 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.
Whilst these are positive results, it should also be taken into account that these trends reflect changes in bat populations from 1997 and it is likely that prior to this, in the second half of the twentieth century, there were significant historical declines in bat populations.
NBMP surveys and data contribute to UK government biodiversity monitoring and reporting obligations including UK and country biodiversity strategies, the Habitats Directive and the national report to EUROBATS. NBMP data contribute to the UK biodiversity indicators which help measure progress towards the Government's target of halting biodiversity loss through a composite index of bat populations.
A number of collaborative projects and partnerships are also ongoing which employ and utilise NBMP data and survey techniques including developing new techniques for woodland bat monitoring, developing a prototype European bat indicator and studying the ecology of urban bat populations.
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