Habitat
Forest edges and openings, semi-open forest, water edges and harvested forest where some structure has been retained. From sea-level - 3,400 m.
Aruba, Belize, Bolivia (NB), Brazil (NB), Canada (B) (P), Colombia, Costa Rica, Ecuador (NB), El Salvador, French Guiana (NB), Guatemala, Guyana (NB), Honduras, Mexico (B), Netherlands Antilles, Nicaragua, Panama (NB), Peru (NB), St Pierre and Miquelon (P), Suriname (NB), Trinidad and Tobago (NB), USA (B), Venezuela (NB).
Vagrant to Greenland.
Breeds from northern and western Alaska eastern across central Canada to Maritime Provinces, and southern in USA to northern California, also locally into north-western Mexico (Baja California), in interior through Idaho and western Montana to north-eastern Arizona and north-western New Mexico and, in east, to boreal regions of Adirondacks and New England. Winters locally in western and southern Mexico (from Jalisco and southern Veracruz) south to Panama and (mainly in mountainous regions) from Colombia and Venezuela south to south-eastern Peru and north-western Bolivia; more locally in the Guianas, southern Amazonia (from lower R Amazon south to central Bolivia and Tapajós basin) and south-eastern Brazil.
 
Population
Estimated population is 1,200,000 (2010) and decreasing.
Status NT
Habitat loss and alteration of forest management practices perhaps limiting breeding success, is the main threat.
For more information see BirdLife International Species Factsheet.
Olive-sided Flycatcher (Contopus cooperi) [XC416924]
by Ed Pandolfino from Fraser-Fort George C, Fraser-Fort George, British Columbia, Canada (song)
Olive-sided Flycatcher (Contopus cooperi) [XC424299]
by Betchkal, Davyd from Hidden Tank, Sitgreaves National Forest, Navajo County, Arizona, United States (call)
Subspecies
No subspecies.
Formerly placed in a monotypic genus, Nuttallornis. Previously referred to as Contopus borealis, but that name preceded by present one. Closest relatives possibly Smoke-colored Pewee (Contopus fumigatus), Western Wood-Pewee (Contopus sordidulus) and Eastern Wood-Pewee (Contopus virens). Larger birds in south-western (southern California, northern Baja California) sometimes treated as a geographical subspecies, marjorinus.