The national population of Marsh Wren is best monitored in Canada by the Breeding Bird Survey (BBS), which covers about half the breeding population. BBS results suggest that the population has shown a fairly consistent increase since the early 1970s, with an over 100% increase in numbers. At the regional level, BBS results suggest large increases in all Bird Conservation Regions for which there are reasonably reliable results, including the Prairie Potholes Bird Conservation Region, which hosts the highest breeding density for this species in Canada. However, results from the Ontario and Quebec Marsh Monitoring Program (MMP) suggest little change in those populations since 1995 and 2004, respectively. It is difficult to compare results between the BBS and MMP because the latter are of shorter duration, cover a smaller portion of the species' range, and there are differences in wetland coverage between the MMP, which targets wetlands, and the roadside BBS. Based on BBS results, the Marsh Wren population is considered to have shown a large increase in Canada and is at an acceptable level relative to its national population goal (see Canada graph below). The continental population has also increased by over 100% since the early 1970s.
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
Additional information on: Quebec Marsh Monitoring Program
Additional information on: Great Lakes Marsh Monitoring Program