Masters Thesis

Latrine site selection and seasonal habitat use of a coastal river otter population

Scent-marking, the deposition of a scent-containing excretion as a means of intraspecific olfactory communication, is common among mammals. For the North American river otter (Lontra canadensis) the latrine serves as a primary area for scent-marking where they regularly deposit scat, urine, and anal sac secretions. Latrine sites provide an efficient means for the indirect study of river otter ecology. This study was conducted on the river otter population located in the Humboldt Bay region of northern California. There were two main areas of focus: the evaluation of otter latrine site selection and examining trends in scent mark deposition at latrines. Paired logistic regression was used to compare models of habitat characteristics present at latrine sites to those at nonlatrine sites, identifying features selected for by river otters in the establishment of latrines. River otters selected for the presence of fallen logs as well as greater water depths and shore heights for the establishment of latrines across the study area. In more forested habitats, greater canopy cover was also selected for latrine establishment. The number of otter scent marks occurring at latrines located in different habitat types was recorded biweekly over the course of a year. Latrine use was compared among habitats using Poisson regression in a mixed model approach, testing the hypothesis that seasonal patterns of habitat use by river otters existed within the study area. Overall trends in seasonal scent mark deposition by river otters at latrines were similar to those found in previous studies, with peaks occurring in the spring and fall. Results suggested that seasonal fluctuations of several prey species influenced the use of habitats by river otters. Information gained through this study may benefit future research efforts by speeding the process of locating river otter latrines, allowing search efforts to focus on areas containing habitat features selected by otters. Seasonal peaks in scent-mark deposition at latrines may also provide optimal times for locating latrine sites and collecting scent marks for use in diet or demography studies. Evidence of seasonal habitat use by river otters provides insight into otter ecology and may also aid future research and land management activities.