Detecting river otter Lontra canadensis latrines near bridges: Does habitat and season influence survey success?

Abstract

During 2006, we conducted riparian surveys to detect river otter Lontra canadensis latrines at 15 bridge-suites along riverine habitats in southwestern Pennsylvania and western Maryland, USA. We defined a bridge-suite as consisting of survey locations at the bridge, a random site and a site chosen by application of a Pattern Recognition Model developed for predicting the location of latrines, with each survey location consisting of both shorelines along a 200-m section of the river. We used occupancy modeling to assess the influence of the continuous covariate SiteScore (a probability derived from Pattern Recognition modeling, with higher scores predicting habitat conditions where river otters are most likely to establish latrines). We also included two categorical covariates with the modeling, each with three factor levels: SiteType (consisting of the three survey locations within a bridge-suite: Bridge, Random and Select, chosen based on having the highest SiteScore among non-Bridge sites within a bridge-suite) and Season (spring, summer and fall) on the probability of detecting a positive site (i.e. a site with >= 1 latrine). The selected model suggested that probabilities of detection were positively related to SiteScore (i.e. habitat quality), higher in spring and fall than in summer, and higher at Selected and Random sites than at Bridge sites. In our study areas, efficacy of surveys to detect river otter signs (i.e. scats at latrines) would be considerably enhanced by considering habitat quality when selecting survey locations and by conducting surveys during spring or fall.