Occupancy of Semi-Aquatic Mammals in an Urban Landscape

Abstract Throughout midwestern North American ecosystems, semi-aquatic mammals including beaver (Castor canadensis), mink (Neovision vision), muskrat (Ondatra zibethicus), and river otter (Lontra canadensis) co-exist in wetlands. These species are ecologically important through their manipulation of habitats and interactions with other species present. Although natural resource managers in urban ecosystems are interested in semi-aquatic mammals and factors affecting their ecology, few such studies exist in the literature. We studied impacts of restoration practices and other environmental covariates on detection and occupancy of the 4 aforementioned focal species on forest preserves managed by the Lake County Forest Preserve District (Lake County, Illinois, USA). Sign surveys were conducted during December-April in 2018-19 and 2019-20. We quantified 12 variables representing bank measurements, temperature, precipitation, soil type, and survey replicate to inform the detection process and quantified 12 variables representing forest cover measurements, aquatic plant measurements, dominant landcover, restoration practices, and anthropogenic disturbances for the occupancy process. Single species, multi-season occupancy models were run in RStudio using the package unmarked. Detection probabilities ranged from 0.10 ± 0.07 for river otters to 0.60 ± 0.03 for muskrats; occupancy probabilities ranged from 0.28 ± 0.18 for river otters to 0.90 ± 0.05 for muskrats. Detection and occupancy were influenced by similar environmental factors (bank measurements, precipitation, and survey replicate for detection; and stream measurements and food availability for occupancy) compared to more rural locations. We provide further evidence that muskrats are urban adapters and document the initial stages of river otter recolonization in the Chicago Metropolitan Area.