Population dynamics of muskrats in experimental marshes at Delta, Manitoba

Abstract

Muskrat populations were studied in relation to water level and vegetation succession in an experimental wetland complex at Delta Marsh, Manitoba, Canada, flooded to three different levels: normal (long-term average elevation); medium (30 cm above normal); and high (60 cm above normal). Trapping in October and May, combined with closed and open population estimators, was usesd to estimate population size, survival, and recruitment. Muskrat densities reached > 30/ha after the second growing season. Populations in medium and high treatments initially reached densities greater than in normal cells, but all populations decreased to < 1/ha in May 1988. Winter survival declined from 0.31 in 1986 to 0.09 in 1987 and recruitment had declined significantly by May 1988. Winter survival, per-capita recruitment, body condition, and winter mass changes were inversely related to population density, but not consistently related to water level treatments. Survival was directly related to winter mass gain although recruitment the following spring was not. The most influential demographic factor in observed declines in density was decreased winter survival, which was consistently low in all treatments once flooding reduced the emergent vegetation. In natural prairie marsh systems, spatial and temporal variation in vegetation response to flooding contributes to variation in the density dependence of both the survival and recruitment of muskrats.