Natterer's bat population trends
The results of the population trends for Natterer's bat from the Hibernation Survey and the Colony Counts are shown on this page, and interpretation of the survey results.
Click here for details on how the population trends are calculated.
Hibernation Survey
UK Index of Natterer's bat from the Hibernation Survey (1997-2011)
Note: The trend for 2011 is shown as a dashed line to indicate that it is provisional. The figure shows trend analysis results (solid line) with 95% confidence limits (dotted lines).
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The index has fluctuated since 1997 but with an overall increase and is currently 80% above the 1999 base year value. This is equivalent to an average annual increase of 5%, a significant upward trend.
Number of Hibernation Survey sites
| Period | Total no. sites | No. sites with bats |
| 2011 | 374 | 188 |
| All years (1997-2011) | 622 | 350 |
Colony Counts
UK Index of Natterer's bat population from Colony Counts (2000-2011)
Note: The trend for 2011 is shown as a dashed line to indicate that it is provisional. The figure shows trend analysis results (solid line) with 95% confidence limits (dotted lines).
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The index is currently 13.6% below the 2000 base year value, equivalent to an annual decrease of 1.3% and there is no significant trend. Note: the baseline year for calculation of this trend is 2000 as very few colonies were counted in earlier years.
Number of Colony Counts sites
| Period | No. sites UK | Colony size |
| 2011 | 38 (35 with bats present) | Average 42 |
| All years (1997-2011) | 89 | Median all counts 38 |
Interpretation of survey results
The significant increase reported from Hibernation Surveys had been sustained for this species for a number of years, although lower counts in the last two years have led to a flattening of this rise. Increase in winter abundance may suggest an increase in the total UK population, but could also reflect other influences on the species' use of hibernation sites.
The trend from the Colony Counts does not reflect that of the Hibernation Survey, but the time series is short and the sample size relatively small, so the power of this survey to detect significant trends is reduced. Recruitment of more sites into the Colony Counts and retention of the existing site network should help to gain a better understanding of the relationship between the results of the two surveys and any overall population change.
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