Drying drives decline in muskrat population in the Peace-Athabasca Delta, Canada

Empirical and anecdotal reports suggest that muskrat are in decline across NorthAmerica, including in the Peace-Athabasca Delta ('Delta'), Canada, one of the largest inland deltas in the world and part of a World Heritage Sitewith 'in Danger' status pending. Muskrat are a key ecological indicator in the Delta. Weinvestigate whether the large-scale loss of critical habitat over the past half-century could be driving a decline in muskrat abundance in the Delta. To do this, we use the Landsat record (1972-2017) to construct a 46 year record of inundation, and compare changes in the extent of critical habitat to the survey record for muskrat (1970-2016) over this 5500 km(2) region. Results showthat the declines in critical habitat and muskrat numbers in the Delta are synchronous: similar to 1450 km(2) of temporarily inundated regions that support critical habitat have diminished by similar to 10 km(2) yr(-1) over the past 46 years, while the muskrat population density (houses/km(2)) has also declined and is significantly related to critical habitat area (km(2)) (R-2 = 0.60, P = 0.0001). These findings have implications for the Delta, a Ramsar Wetland of International Importance in part for its role as a habitat for nearly 200 species of birds, many ofwhich rely on the aquatic habitat considered here. Our results further suggest that the loss ofwetland habitat is a primary driver of the decline of muskrat across the species' native range.