Non-invasive genotyping and spatial mark-recapture methods to estimate European pine marten density in forested landscapes

Abstract

Accurate population density estimates are important for conservation but can be difficult to obtain where species are elusive or rare. Non-invasive genotyping from hair or faeces has provided a promising solution and allowed individual identification from genotypes to inform population assessment models. We use individual genotypes derived from hair samples and Spatially Explicit Capture Recapture (SECR) models to estimate the population density of European pine marten (Martes martes) in three Scottish forests, then examine the effects of forest fragmentation on population size. Relative trends in pine marten abundance can be observed via changes in the number of scats in an area through time, but the link between this measure and population density remains unclear. We provide the first calibration of scat counts to enable population density estimation without the need for genetic analysis. Population density estimates ranged from 0.07 km-2 (95% CI 0.03 – 0.16) to 0.38 km-2 (95% CI 0.11 – 1.07), which were mid to low compared to other estimates from the Scottish population. An unequal sex ratio was found in one of the three forests. We found support for the previous finding that pine marten density in Scotland increases with forest fragmentation up to a threshold level (20 – 35% forest cover), beyond which it decreases. Our calibration suggests a non-linear relationship between scat counts and population density, although relatively small changes in population density result in marked changes in scat number. Following the recent re-introduction of pine martens to Wales, non-invasive genetic sampling for population estimation may provide an effective way of monitoring their progress.