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. The Canada warbler is protected at the federal level in both Canada and the United States. John James Audubon illustrates the Canada warbler in Birds of America (published, London 1827-38) as Plate 73 entitled "Bonaparte's Flycatching-Warbler—"Muscicapa bonapartii"." The single female (now properly identified as a Canada warbler) is shown perched in a Great Magnolia ("Magnolia grandiflora") branch that was painted by Joseph Mason. The final, combined image was engraved and colored by Robert Havell Jr. at the Havell workshops in London. The original painting was purchased by the New York Historical Society.