The Breeding Bird Survey (BBS) is the best available source of monitoring data for the Wilson's Warbler, despite covering only about one-third of the species' breeding population. BBS annual indices (see graph below) indicate a decrease in abundance until the late 1990s, but the magnitude of change (22%) is within the range considered to be relatively similar to those in the early 1970s. However, results vary among the various Bird Conservation Regions (BCRs) in which the species occurs and for which there are reasonably reliable results (displayed below). Several BCRs show decreases greater than 50%. Reliable results are not available for the Canadian portion of the Northwestern Interior Forest BCR, where breeding densities are high. Interestingly, the results for that entire BCR, including data from Alaska, suggest a strongly declining trend (60%; Smith, A.C. ECCC, pers. comm.). In contrast to the population status in Canada, results from the BBS from throughout North America indicate a large decrease in the continental population. Considering all information, the species is perhaps best assessed as having shown little overall change relative to 1970, but the reliability of this assessment is considered medium because of poor coverage in its northernmost range and evidence to suggest the possibility of a stronger decrease. The Wilson's Warbler is currently at an acceptable level relative to its national population goal (see BBS Canada graph below), though if the small decrease continues, it may drop below this level in future.
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis