Muskrats ondatra zibethicus are semiaquatic herbivores experiencing long-term population declines in north america, including the great lakes basin

This economically important furbearing species is also culturally significant across north america, including within the great lakes basin. As a result of foraging behaviors thought to limit the expansion of invasive plant species and promote wetland heterogeneity, muskrats positively affect wetland biodiversity in wetlands which they occupy. Thus, this historically common species may be considered an ecosystem engineer in wetland communities. Continued declines in muskrat populations will likely have adverse effects on muskrat trappers, wetland biodiversity, and overall wetland conservation that will last decades. Understanding the causes of local population declines will be critical for informing management and population recovery at the regional level in the great lakes basin and possibly beyond.reasons for long-term regional declines of muskrat populations, including in the great lakes basin, remain unknown to wildlife professionals, trappers, and other interested groups. However, recent studies have revealed differences in muskrat population health and disease risks between regions with relatively pristine wetland habitats i.e., voyageurs national park, northern MN and heavily degraded wetland habitats i.e., central IL . In one of the first efforts to evaluate muskrat declines throughout the entire great lake basin, the preliminary results from our previously great lakes fish and wildlife restoration act funded proposal, assessing the value of an indicator species for wetland quality, connectivity, and wildlife in the great lakes basin , provided a foundation for a focused investigation for these population declines. In that proposal, we collected, organized, and analyzed numerous large-scale datasets to assess potential factors that may impact muskrat populations occurring throughout the great lakes basin. Our results suggested at least two underlying drivers of muskrat population dynamics as indexed by harvest multi-year drought conditions and vegetative disturbance within wetlands as broadly measured using a floristic quality index . Degradation of wetland quality, through drought and altered vegetation characteristics, can negatively affect muskrat health and reproduction, both important to muskrat population growth.given the potential relationship between muskrat populations and these factors, the next step in our investigation is a field-based effort to collect data on muskrat population health and demography across a gradient of drought conditions and vegetative disturbances throughout the great lakes basin. These data will help uncover mechanistic explanations for observed population declines and also help inform regional management efforts for muskrat populations and wetland complexes. Our goal is to investigate how wetland condition determined by drought and vegetation disturbances impact the population structure, reproduction, and health of muskrats using information from carcasses collected from wetland sites positioned across a gradient wetland quality throughout the great lakes basin. Our objectives include 1. To assess population structure based on SEX and age ratios of harvested muskrats.2. To assess reproduction based on examinations of carcasses of female and male muskrats.3. To assess individual and population-level health based on body-FAT content and or levels of contaminants.4. To collect site-specific wetland data, including floristic quality index and other variables e.g., HUT counts associated with wetland condition and incorporate these variables into all analyses.to meet our goal, the project team includes several state, tribal, and federal agency partners, and coordination with several other organizations.