Evaluating unoccupied aerial vehicles for estimating relative abundance of muskrats

Due to muskrat (Ondatra zibethicus) population declines in North America, it is important to develop rapid, safe, and economical tools for estimating abundance over large spatial and temporal scales. During November 2020–February 2021, we assessed unoccupied aerial vehicles (UAVs) at Bear Creek Flooding State Wildlife Management Area in the northern Lower Peninsula of Michigan. We examined aerial red-green-blue (RGB) and thermal imagery for estimating the total number of muskrat houses during a snow-free and snow-cover period relative to ground surveys. Muskrat house counts were similar between the December snow-cover UAV RGB image survey and February ground survey (V = 70, P = 0.559), but 132% and 136% lower for November snow-free UAV survey compared to snow-cover UAV (V = 203.5, P < 0.001) and ground (V = 196, P < 0.001) surveys, respectively. Unoccupied aerial vehicles can rapidly, safely, and economically estimate and track relative abundance of muskrats in wetlands that have some snow cover and should be evaluated further in more systems at different times of the year. Effective use of UAV imaging for muskrat house surveys is dependent on time of day, temperature, and weather conditions. Conducting UAV surveys in tandem with ground surveys would improve estimates of relative abundance if active muskrat houses are better defined.