Effects of flooding and riparian buffers on survival of muskrats (Ondatra zibethicus) across a flashiness gradient

Abstract

Increased agricultural production within the Grand Prairie region, USA, has resulted in drainage of most natural wetlands within the landscape. Muskrats ( Ondatra zibethicus (L., 1766)) in this region have shifted much of their distribution to riparian habitats that have unstable flow regimes and flood inundation times that could be related to position within watersheds. We investigated predation risk of radio-marked riparian muskrats during flooding events in relation to landscape position. We used known-fate models and an information–theoretic approach to examine effects of age, season, hydrology, and riparian width on weekly survival rates. During flooding events, muskrats positioned farther from headwaters were displaced for longer, as well as exposed to predation from terrestrial predators for longer, than those positioned closer to headwaters. However, this increased exposure during floods did not translate into lower survival because most mortalities were due to predation by American mink ( Neovison vison (Schreber, 1777)) along stream edges during nonflooding periods. Weekly survival of muskrats was lower in winter (mean = 0.9377, SE = 0.1793) than in nonwinter (mean = 0.9770, SE = 0.0116) and was positively related to riparian width. Larger riparian buffers can increase muskrat survival in small streams and agricultural ditches within highly altered, human-dominated agroecosystems. Our study provides a rare example of linking riparian buffers to fitness for a stream-associated organism.