Marsh interspersion and muskrat (Ondatra zibethicus) habitat use

Muskrat (Ondatra zibethicus) populations have been declining in North America for decades. The precise cause of these widespread declines has not yet been identified. Over a similar timeframe, wetlands across large regions of North America have been experiencing an invasion of cattails (Typha). Non-native T. angustifolia readily hybridizes with native T. latifolia to produce T. x glauca, which tends to dominate over parental species and other wetland plants alike. T. x glauca invasions are associated with many negative consequences for wetlands, including a reduction in biodiversity, open water habitat, and interspersion of water and vegetation. Muskrats are strongly tied to wetlands, especially where there is a high degree of interspersion of water and emergent vegetation. Therefore, a widespread reduction in interspersion caused by T. x glauca invasions may be contributing to widespread muskrat population declines. We sought to understand the impact of reduced marsh interspersion on fine-scale muskrat habitat use which will shed more light on broad-scale population trends. We measured intensity of habitat use by muskrats in a large, Typha-dominated marsh in south-central Ontario using remote cameras, stratifying camera placement along a gradient of marsh interspersion. We found no correlation between interspersion and intensity of use, suggesting that factors other than interspersion may drive intensity of use. Our study site, like most marshes in the region, was highly dominated by T. x glauca. Further research is needed to determine the impact of T. x glauca invasions on muskrats, as well as the cause of widespread muskrat declines. Keywords: muskrats, intensity of use, camera traps, invasive species, Typha, wetlands