Threats to the Canada warbler include forest fragmentation; over-browsing of the understory by deer, acid rain, and the spread of the woolly adelgid (a killer of fir and hemlock trees). Owing to these factors the Breeding Bird Survey data show a population decline of 3.2 percent per year throughout the Canada warbler's breeding range, with the greatest declines in the Northeast. The species has been assessed as "threatened" by the Committee on the Status of Endangered Wildlife in Canada. The IUCN, however, ranks the Canada warbler as a species of least concern.