Muskrat populations in Canada and the U.S. do not necessarily behave the same: an examination of population cycles and Moran effects based on harvest data.

Analyses of harvest data (1925 – 1949) from the Hudson Bay Company in Canada have suggested that some populations of muskrats (Ondatra zibethicus) show cycles that may be related to predator-prey relationships with American mink (Neovison vison). We examined harvest data (1970 – 2011) from the U. S. for comparison. After controlling for economic influences on harvest (e.g., pelt price), we found no evidence that muskrats showed population cycles in our 41-year data set. Muskrat and mink dynamics were highly correlated without time lags, providing no support for a classic predator-prey cycle. Muskrat harvest was related to seasonal weather conditions in a few states, but factors related to harvest varied by state. Autoregressive models, usually interpreted to infer density dependence, showed the greatest power for predicting population dynamics, but the mechanisms underlying the relationships remain unclear. We caution against making generalizations about “North American muskrats” based on data from a limited part of their geographic range, and especially without controlling for factors affecting trapper effort and participation.