Williamson's Sapsucker Sphyrapicus thyroideus Scientific name definitions

Inhabiting open coniferous and mixed coniferous-deciduous forests of western North America, Williamson's Sapsucker has been considered a sensitive indicator species because of its specific habitat requirements. Like other sapsuckers, it drills conspicuous rings of holes (“sap wells”) into tree trunks, specializing on coniferous sap and phloem. Breeders switch to a diet of ants during the nestling period.

Unlike all other woodpeckers, Williamson's Sapsucker exhibits spectacular sexual differences in plumage. Males are black with bright red, yellow, and white, while females are mostly cryptic brown with little contrast except for their yellow bellies. These plumage differences confused early naturalists, who thought the two sexes were separate species. John Cassin first described the species as Picus thyroideus in 1851 from two adult female specimens secured by John Graham Bell while on a collecting trip to California in 1849–1850 (1 Cassin, J. (1852). Description of birds of the genera Laniarius, Dicrurus, Graucalus, Manacus and Picus, specimens of which are in the collection of the Academy of Natural Sciences of Philadelphia. Proceedings of the Academy of Natural Sciences of Philadelphia 5(1851):347-349. Close ). Cassin (2 Cassin, J. (1856). Illustrations of the birds of California, Texas, Oregon, British and Russian America. Philadelphia: J. B. Lippincott. Close ) changed the genus provisionally to Melanerpes and applied the first common name, Black-breasted Woodpecker. John Newberry (3 Newberry, J. A. (1857). Zoological Report no. 2. In Report of Explorations and Surveys to Ascertain a Route for a Railroad to the Columbia River (H. L. Abbott, Editor). U.S. War Department Reports of Explorations and Surveys 1855–60. Washington, DC, USA. Close ) collected a male in 1855 in southern Oregon near Klamath Lake and named it Williamson's Woodpecker (Picus williamsonii). Both “species” were renamed under the new genus Sphyrapicus by Baird (4 Baird, S. F. (1858). Part 2. General report upon the zoology of the several Pacific railroad routes. Reports of explorations and surveys to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean, 1853-1856. Vol. 9. Washington: War Dept. Close ); two other common names of thyroideus included Brown-headed Woodpecker (5 Baird, S. F. (1858) Catalogue of North American Birds chiefly in the museum of the Smithsonian Institution. Smithsonian Institution, Washington, DC, USA. Close ) and Round-headed Woodpecker (6 Cooper, J. G. (1870). Ornithology. In Geologic Survey of California. Volume 1: Land birds (S. F. Baird, Editor), Cambridge University Press, Cambridge, United Kingdom. Close ).

The confusion between sexes and species ended when Henry Henshaw verified in 1873 that the two were a single species when he observed a mated pair at a nest in Colorado to which he applied the common name Black-breasted Woodpecker (7 Henshaw, H. W. (1875). Report upon the ornithological collections made in portions of Nevada, Utah, California, Colorado, New Mexico, and Arizona during the years 1871, 1872, 1873, and 1874, by H. W. Henshaw. In Report Upon Geographical and Geological Explorations and Surveys West of the One Hundredth Meridian (G. M. Wheeler, Editor), U. S. Government Printing Office, Washington, D.C., U.S.A. pp. 131-508. Close ). The first ornithological compilation to treat both species as one was Coues (8 Coues, E. (1874). Birds of the Northwest: A Hand-book of the Ornithology of the Region Drained by the Missouri River and its Tributaries. U.S. Geological Survey Miscellaneous Publications, No. 3. U.S. Geological Survey, Washington, DC, USA. Close ) using the common name “Black-breasted or Williamson's Woodpecker.” The name sapsucker came into use after being applied to Sphyrapicus in the first checklist of American Ornithologists' Union in 1886, which also standardized the common name Williamson's. The species was named after Lieutenant Robert Stockton Williamson (1824–1882), who conducted early railroad surveying expeditions in the West Coast states (9 Mearns, B. C., and R. F. Mearns (1992). Audubon to Xántus: The lives of those commemorated in North American bird names. Academic Press, New York, NY, USA. Close ), including the expedition upon which John Newberry collected the first male specimen.

Williamson's Sapsucker populations had a stable trend overall from 1966–2019 based on Breeding Bird Survey (BBS) routes. In Canada, the species' status was designated as Endangered in 2005, and that assessment was re-confirmed in 2017, because of small populations and habitat loss of mature western larch (Larix occidentalis) forests, a key habitat for the species.