The best source of information on the population status of Mourning Warbler in Canada is the Breeding Bird Survey (BBS). Overall reliability of the BBS is considered high because it samples a high percentage of the Mourning Warbler's breeding range, and there is high precision in its trends. BBS data indicate a stable population until a steep decline in the 1990s, followed by a period of decline at a lower rate. The current population is approximately 54% lower than in the early 1970s. Similar patterns in decline have occurred in all Canadian Bird Conservation Regions with medium or high reliability trends, except for southern Ontario and Quebec, where there has been little change over the long term.

The goal for Mourning Warbler is to increase the population to the level it was at in the early 1970s, based on the Breeding Bird Survey. Trend data show that Mourning Warbler is currently below its goal range and continuing to decline. Analysis considering the historical population loss and recent trend suggests that it is unlikely that the goal can be met by 2050, so the interim target is to reach 90% of the goal by 2050. Achieving this target, and ultimately reaching the national goal for this species, will require deliberate conservation action.