The Williamson's Sapsucker, a sensitive indicator species, is a medium-sized woodpecker exhibiting sexual dimorphism. Males have iridescent black upperparts, head and breast, alongside a white eye and mustache stripe, red throat and all black tail. Females have upperparts, wings and flanks barred with white, brown and black. In addition, females have a brown head and black tail with black and white barring in the middle. However, both sexes share a white rump and yellow belly. Adult females may be confused with juvenile Yellow-bellied (Sphyrapicus varius) or juvenile Red-naped (S. nuchalis) sapsuckers, but may be distinguished from both by its uniformly brown head with no red and lack of white wing-coverts.

References cited in Species Profile

• Cornell Lab of Ornithology. 2015. Williamson's Sapsucker (Sphyrapicus thyroideus). Birds in Forested Landscapes. http://www.birds.cornell.edu/bfl/speciesaccts/wilsap.html
• Dobbs, R. C., T. E. Martin, and C. J. Conway. 2012. Williamson's Sapsucker. The Birds of North America Online. http://bna.birds.cornell.edu/bna/species/285/articles/introduction