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Detecting population change

The purpose of the NBMP is to allow us to draw accurate conclusions about what is happening to our bat populations. We need to be able to identify any significant changes to these populations, and in particular identify possible declines early on, so that swift conservation action can be taken.

The NBMP uses a detection system which is aimed at identifying problems at an early stage. The detection system follows that used by the British Trust for Ornithology which identifies Red and Amber alerts for individual species population trends as follows:

  • Red alert: Severe decline of 50% or more over 25 years (equivalent to a 2.73% decline per year)
  • Amber alert: Moderate decline of between 25-49% over 25 years (equivalent to a 1.14% decline per year)

An assessment based on power analyses and the width of the confidence limits for the current trend estimates suggests that our samples sizes should be sufficient to detect an Amber or Red Alert change within 25 years at most.

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0345 1300 228