Now you see me, now you don’t: Why population trends should account for imperfect detection
Date:
Summary
The accurate monitoring of population trends is vital both in order to identify drivers of change and to prioritise species most in need of conservation. Indices such as IUCN Red-Lists frequently use occupancy data to assess population patterns. Such data is typically obtained by periodically revisiting a suite of sites and recording whether the species was observed. This approach implicitly assumes that if the species is present we are certain to detect it, however this is almost never the case. Imperfect detection will therefore create biases in trend estimates. Here we estimate occupancy trends across Switzerland for 14 amphibian species, using both a method that controls for detection probability and a ‘naïve’ estimate which assumes detection is perfect. We also map these measures onto Red-List criteria to illustrate how ignoring detection probabilities can overestimate extinction threat.