Habitat selection by muskrats in experimental marshes undergoing succession

Abstract

I analyzed habitat selection by muskrats (Ondatra zibethicus) in relation to density and plant succession in an experimental wetland complex flooded to three different levels: normal (long-term average elevation), medium (30 cm above normal), and high (60 cm above normal) at Delta, Manitoba. Locations where muskrats were trapped or built lodges were superimposed on vegetation types and water depth, in a geographic information system, to determine habitat selection. More than 60% of all individuals were captured in stands of Scirpus, Scolochloa, or Typha, and muskrats significantly avoided areas with water < 1 cm that were dominated by annuals and Hordeum. Muskrats preferred Typha and Scirpus stands for lodges, although some lodges were built in Scolochloa and Phragmites. Water depth at lodges averaged 38 cm, and > 90% of lodges were located in water ≥ 10 cm. Tall dense emergent growth trapped the most snow, resulting in the ice being less thick. Muskrats first captured in Typha or Scirpus stands gained significantly more mass during winter than did those captured in all other habitat types. As emergent vegetation changed and muskrat population density increased, the selection of habitat such as Typha in moderately deep water changed less than did the selection of habitat in shallow water or of those dominated by Scolochloa or sparse Scirpus. These data confirm density-dependent habitat selection by muskrats and suggest that spatial complexity induced by wetland succession is important in muskrat population dynamics.