The best source of information on the population status of Canada Warbler is the Breeding Bird Survey (BBS), although slightly less than half of the species' breeding population is covered by the survey and the northernmost portion of its range is poorly covered. BBS data indicate a continuous long-term decrease in abundance since the early 1970s, with an overall loss of about 63% of the population. That decrease has continued through the most recent decade though at a smaller magnitude. Declines are seen in all Bird Conservation Regions that host the species and for which there are reasonably reliable results (displayed below). BBS data from throughout North America demonstrate the decrease is continent-wide. Information from the various breeding bird atlases provide some corroborating evidence of a decline. The Maritimes atlas found little change in distribution but a dramatic decrease in the probability of Canada Warbler observations between the first (1986-1990) and second (2006-2010) atlas periods (Stewart 2015). About half the population breeds in Ontario, where a decrease in the probability of observation was found between atlases (mid-1980s to mid-2000s; see table below). Preliminary results from the Atlas of the Breeding Birds of Quebec 2017 suggest there were more atlas squares with breeding evidence in the second atlas (2010-2014) compared to the first (1980-1989). However, this may reflect increased search effort and better coverage in the boreal during the second atlas. Relying mainly on the BBS, the Canada Warbler is best assessed as having shown a large decrease in population since the early 1970s and is considered to be below the lowest acceptable level relative to its national population goal (see Canada graph below). This goal is consistent with the Canada Warbler Recovery Strategy's short-term objective to halt the decline and long-term population objective to ensure a positive population trend (Environment Canada 2016b).
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
Additional information on: Atlas of the Breeding Birds of Ontario