Field identification tips: In common with other sapsuckers (genus Sphyrapicus), the male Williamson's Sapsucker (Sphyrapicus thyroideus) has a prominent white patch on the wing, visible even when the wing is folded. The male is dark overall with black back and wings, accented by white stripes on the face and a yellow belly. Female Williamson's Sapsuckers, unlike all other North American woodpeckers, looks very different from the male, with brown and white bars over the back and wings, and is the only sapsucker with no white wing patch. However the female has the yellow belliy in common with the male. The sexual dimorphism is so extreme that in 1852 John Cassin originally described females as the Black-breasted Woodpecker (Picus thyroideus) while in 1855 John Newberry described the male as Picus williamsonii. Spencer Baird later reclassified both "species" in the genus Sphyrapicus, along with the other sapsuckers. But because the male and female looked so different, no one questioned the existence of two species. It wasn't until 1873 that Henry Henshaw observed that the two "species" were actually female and male of the same species.