_Breeding range._--Williamson’s sapsucker breeds =north= to central Washington (Bumping Lake and probably Dayton); and southwestern Montana (Missoula, Pipestone Creek, Bridger Creek, and Red Lodge). =East= to Montana (Red Lodge); Wyoming (Yellowstone National Park and Laramie Peak); Colorado (Estes Park, Idaho Springs, Breckenridge, El Paso County, and Fort Garland); and New Mexico (Carson Forest, Santa Fe Canyon, Las Vegas, and Hermosa). =South= to southern New Mexico (Hermosa); Arizona (Tucson, Mogollon Mountains, and Fort Whipple); and southern California (San Jacinto). =West= to eastern California (San Jacinto, San Bernardino Mountains, Pyramid Peak, Tuolumne County, Echo Lake, Lake Tahoe, Lassen Peak, and Eagle Peak); western Oregon (Rogue River Valley and Foley Springs); and west-central Washington (Bumping Lake). _Winter range._--In winter the species is regularly found =north= to central California (Yosemite Valley); central Arizona (Pine Springs, Oak Creek, and Mogollon Mountains); southwestern New Mexico (Black Range); and central Texas (San Angelo). =East= to Texas (San Angelo and probably Kerrville); eastern Chihuahua (Apache); and Jalisco (Bolanos and Guadalajara). =South= to southern Jalisco (Guadalajara). =West= to Jalisco (Guadalajara); northwestern Durango; western Chihuahua (Refugio, Casa Colorado, Bavispee River, and Colonia Garcia); northern Baja California (San Pedro Martir, Ville de la Trinidad, and Hanson Lagoon); and California (Pasadena and Yosemite Valley). As outlined, the range applies to the entire species, which has been separated into two subspecies. True Williamson’s sapsucker (_S. t. thyroideus_) is found in the Pacific coast region from British Columbia south to Baja California, while Natalie’s sapsucker (_S. t. nataliae_) inhabits the Rocky Mountain region from Montana south to Jalisco. _Spring migration._--Although the species appears to be resident throughout considerable portions of its range, and but little is known of its migratory movements, the following early dates of arrival have been noted: Colorado--Boulder County, April 5; Colorado Springs, April 5; Evergreen, April 8; Denver, April 15. Wyoming--Yellowstone Park, April 29. Montana--Charcoal Gulch, April 23. Nevada--Carson City, March 10. Washington--Pullman, April 26. A late date of departure from the southern part of the winter range is Chihuahua, Palomas Lakes, April 7. _Fall migration._--Available late dates of fall departure are: Washington--Copper River, September 3. Oregon--Rustler Peak, November 6. Nevada--Lee Canyon, October 7; Carson City, November 27. Montana--Fort Custer, September 9. Wyoming--Yellowstone Park, September 22; Wheatland, October 4. Colorado--Del Norte, September 5; Rio Blanco, September 9; Boulder County, November 6. It has been noted to reach Hanson Lagoon, Baja California, on October 11.