DOI: 10.5061/dryad.b2rbnzsf2
title: Data from: Historical surveys reveal a long-term decline in muskrat populations

description: 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.
description: 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.
description: Two .csv files are provided, each containing house count totals
 by year for each survey area: 
 <strong>Sadowski_2021_HistoricMuskratSurveys_TotalHouseCountData_AllYearsandSites.csv </strong>- 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). <strong>Sadowski_2021_HistoricMuskratSurveys_PeleeHouseCountsByZone_AllYears.csv </strong>- 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.