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Data from: Historical surveys reveal a long-term decline in muskrat populations

Cite this dataset

Sadowski, Carrie; Bowman, Jeff (2022). Data from: Historical surveys reveal a long-term decline in muskrat populations [Dataset]. Dryad.


The muskrat (Ondatra zibethicus) is an iconic species in Canada, valued for both its fur and its integral role in wetland ecosystems, and widely regarded for its perseverance. However, the resilience of this semi-aquatic mammal seems to be in question now as increasing evidence points to widespread population declines. Recent analyses of harvest data across North America suggest a reduction in their numbers, but this has not been widely corroborated by population surveys. In this study we replicated historic muskrat house count surveys at two large Great Lakes coastal wetlands and present confirmation that declines in muskrat harvest correspond to actual declines in muskrat abundance. At the Point Pelee National Park marsh and the Matchedash Bay-Gray Marsh wetland we found that mean muskrat house counts declined by 93% and 91% respectively between historic surveys 40-50 years ago and contemporary surveys over the past seven years. The factors responsible for these dramatic declines remain unclear but there may be a relationship with changes in the habitat quality of these wetlands that have occurred over the same time frame. Not only is the loss of muskrats an issue for the resulting loss of the wetland ecosystem services they provide, but it may be an indication of broader marsh ecosystem degradation. As such, a scarcity of muskrats should be considered a red flag for the state of biodiversity in our wetlands. Continued surveys and ongoing research are needed to shed more light on the current status of muskrat populations and their marsh habitats across their native range.


This dataset was collected by conducting annual field surveys for muskrat houses in two large wetlands in Ontario, Canada over two different time periods, each comprising several years of surveys: a historic survey period between 1957-1986 and a contemporary survey period between 2014-2019.  Surveys were conducted at the Point Pelee National Park marsh and the Matchedash Bay-Gray Marsh wetland.

Historic data was compiled by this dataset's authors by obtaining historic survey reports and extracting muskrat house count data provided in these reports. Contemporary data was collected by this dataset's authors by revisiting historic survey sites and replicating the historic survey methods, as described in the historic survey reports and in the manuscript published from this dataset. 

The data presented here are numbers of new or active muskrat houses found in each study area during each survey year.  The data have not been processed; only grouped into different categories, as indicated in the data tables.

Usage notes

Two .csv files are provided, each containing house count totals by year for each survey area: 

Sadowski_2021_HistoricMuskratSurveys_TotalHouseCountData_AllYearsandSites.csv - Table containing all total muskrat house counts for each year surveyed during each survey period, at each study site (Pelee and Matchedash). Data are presented in different columns related to different categories of the analysis: all survey years and zones combined; standardized survey years and zones only; contemporary totals based on ground counts only; contemporary totals based on ground counts supplemented with aerial imagery counts. Fields without count totals are populated with descriptive text to indicate why there is no house count for that survey year in that particular column (category).

Sadowski_2021_HistoricMuskratSurveys_PeleeHouseCountsByZone_AllYears.csv - Table presenting a breakdown of the total muskrat house counts for each year surveyed by each of the 15 survey zones at the Point Pelee marsh, where breakdown data could be found.  Text notes are provided in file below table to explain why certain years have incomplete survey data. 



Ministry of Natural Resources and Forestry