When is a species declining? optimizing survey effort to detect population changes in reptiles

Abstract

Biodiversity monitoring programs need to be designed so that population changes can be detected reliably. This can be problematical for species that are cryptic and have imperfect detection. We used occupancy modeling and power analysis to optimize the survey design for reptile monitoring programs in the UK. Surveys were carried out six times a year in 2009-2010 at multiple sites. Four out of the six species - grass snake, adder, common lizard, slow-worm -were encountered during every survey from March-September. The exceptions were the two rarest species - sand lizard and smooth snake - which were not encountered in July 2009 and March 2010 respectively. The most frequently encountered and ..