Assessing winter habitat selection by river otters using aerial surveys

River otters (Lontra canadensis) are widespread in the United States and are managed for sustainable fur harvest throughout much of their range in the United States. Despite their widespread distribution, river otters can be difficult to monitor due to their cryptic nature and the inaccessible habitats they often occupy. Additionally, there has been little research conducted to quantify winter habitat selection patterns of river otters. We used 4 years of aerial survey data conducted during the winter to quantify habitat selection patterns of river otters in Wisconsin, USA, and to determine factors associated with survey efficacy. We used a mixed-effects logistic regression framework to evaluate habitat and anthropogenic factors at 2 spatial scales. We found that river otters were positively associated with the amount of forested and wetland habitat within a 1 km buffer around sampling locations, but that no factors we measured were influential at a local (100 m) scale. River otters were more likely to be detected when ice cover was only partial as opposed to when ice coverage was complete or when it was completely absent. Our results suggested that river otter habitat selection in Wisconsin is not strongly affected by anthropogenic influences but instead by broad-scale habitat configuration. Furthermore, our results suggested that aerial survey approaches for river otters can be optimized by conducting surveys during periods when ice coverage is sufficient to allow for clear tracking substrate without being prevalent enough to limit movements into and out of corresponding aquatic habitats.