The Canadian population of Olive-sided Flycatcher is best monitored by the Breeding Bird Survey (BBS), which is well-suited to detecting the species and has high precision. It poorly samples the northern part of the breeding range, which limits reliability of the survey to medium. The national trend shows a steady decline since the early 1970s, steepest in the 1990s but still ongoing, with a total loss of 74%. The trend has been similar throughout its Canadian breeding range, and is also reflected in the breeding bird atlases for Ontario, Quebec, and the Maritimes, which all show declines relative to the initial surveys in the 1980s and early 1990s.

The goal for Olive-sided Flycatcher is to increase the population to the level it was at in the early 1970s, based on the Breeding Bird Survey. Olive-sided Flycatcher 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 50% of the goal by 2050. Achieving this target, and ultimately reaching the national goal for this species, will require deliberate conservation action. This is consistent with the Recovery Strategy for Olive-sided Flycatcher under the Species at Risk Act, which calls for halting the decline by 2025 and ensuring a positive trend thereafter, while at least maintaining its current extent of occurrence in Canada (Environment Canada, 2016).