Detectability of the Eurasian otter by standard surveys: an approach using marking intensity to estimate false negative rates

摘要: False negative detections may bias the surveys for rare species and reduce reliability of models based on proportion occupied patches. We assessed detectability Eurasian otter Lutra lutra through standard survey method by analysing detection history 28 sampling stretches surveyed monthly between March 2001 January 2003. Each spraints was considered as a false if had been recorded in previous and/or following month (respectively, cFN FN). Otter marking intensity (MI) (MI=N° per kilometre) calculated assumed to represent an index its relative abundance. Spraints were found 81.7% all surveys. Yearly MI ranged from 1.02 101.4 kilometre. In 2002, mean significantly lower than year, while no clear seasonal trend could be outlined. The minimum number required establish occurrence otter, estimated probability model, 2.6 inversely related MI. For sub-sample 18 stretches, relation frequency both FN five variables potential interest otters tested means stepwise linear multiple regressions, yielding two highly significant models, which included only explanatory variable. correlated resulting equations used assess percentage positive years. After correction non-detections, site occupancy did not vary 2 years, except one river when applying more conservative estimate negatives (cFN). Multiple visits assessing should become components This approach has broad applicability applied large-scale distribution other or elusive mammalian carnivores.