The uniquely patterned White-headed Woodpecker is restricted to mixed coniferous forests dominated by pines (Pinus spp.) in the mountains of far western North America, from south-central British Columbia to southern California. Pine seeds are an important part of its diet through much of the year but especially in fall and winter. Individuals typically take pine seeds from open cones or by perching directly on an unopened cone and drilling into it. The species is closely associated with the ponderosa pine (Pinus ponderosa) over most of its range, but reaches greatest abundances where 2 or more species of pines with large, seed-laden cones occur. Its diverse foraging repertoire also includes flaking and gleaning of the trunk and branch surfaces of living conifers, as well as probing of needle clusters. These birds rarely, if ever, drill deeper into live, decaying, or dead wood.
Pine seed predation and relatively superficial bark foraging distinguishes the White-headed Woodpecker ecologically from its sympatric and similar-sized relative, the Hairy Woodpecker (Picoides villosus). The White-headed Woodpecker is generally sedentary, although some movement within mountain ranges has been documented and there are records of wanderers to lowland regions up to 150 km from known breeding areas. Modern forestry practices, including clear-cutting, even-age stand management, snag removal, fire suppression, and forest fragmentation have contributed to local declines of this species, particularly north of California.
This is a territorial, monogamous breeder, with some evidence that pairs remain bonded through the winter. No seed-caching behavior or attendant social behaviors have evolved, undoubtedly because the pine seeds utilized are usually extracted in pieces from unopened cones and cannot be stored whole. Pairs usually excavate nests in snags, stumps, dead portions of living trees, or logs; nest sites on average are lower than those of sympatric woodpecker species, often within 3 meters of the ground.
The relationships of the White-headed Woodpecker to other “pied woodpeckers” of the genus Picoides are uncertain, although its closest relatives are hypothesized to be the Hairy and Strickland's (P. stricklandi) woodpeckers. This woodpecker was one of many western bird species originally described by John Cassin (Cassin 1850a), in this case from a specimen secured by John Graham Bell in the gold rush country of the west slope of the Sierra Nevada in El Dorado County, California; Cassin assigned it to the genus Leuconerpes Swainson. Derived plumage characters and the relatively short tongue of the White-headed Woodpecker inspired the recognition of the monotypic genus Xenopicus by Baird, Cassin, and Lawrence (Baird et al. 1858). A weakly differentiated subspecies from the mountains of southern California, described by Grinnell (Grinnell 1902c), continues to be recognized by the American Ornithologists' Union (1957). The White-headed Woodpecker remains one of the most poorly studied woodpeckers in North America.