Many kinds of wildlife will sample the sweet taste of tree sap when it’s easily available. Various woodpeckers will occasionally drill into bark to get access to the sap. But the four species of sapsuckers of North America are unique in their degree of specialization on this resource, regularly drilling rows of “sap wells” in trees and then returning to sip the sticky treat as it oozes out.
Three of the sapsuckers — Yellow-bellied, Red-naped, and Red-breasted — are common and widespread, collectively found from coast to coast. They are very close relatives, differing mainly in the amount of red on the head, and they were formerly lumped into one species. But the fourth, Williamson’s Sapsucker, is highly distinctive. A specialty of western mountains, it is uncommon and elusive, a prize for birders.
The breeding range of Williamson’s Sapsucker extends from southern British Columbia south to the mountains of southern California, northern Baja, northern Arizona, and central New Mexico. It winters in the southern part of this range and well south into Mexico. At all seasons it occurs mainly in the mountains, but a few show up at low elevations in migration and winter. Stray migrants have appeared east to Louisiana and the Great Lakes, and one once was found on Long Island, New York.
So, although the species is extremely rare east of the Great Plains, birders everywhere have reason to watch for it.
Even within its normal range, Williamson’s Sapsucker can be hard to find. Sapsuckers in general are often quiet and inconspicuous, but Williamson’s is also very uncommon everywhere. It’s more specialized in habitat than other sapsuckers. Where its breeding range overlaps with those of Red-naped and Red-breasted Sapsuckers, those two may be found in coniferous, mixed, or deciduous forest, including pure stands of aspen or cottonwood. Williamson’s, by contrast, is very strongly tied to conifers such as pine, fir, larch, and Douglas-fir. It’s also more specialized in its diet. Other sapsuckers are known to dig sap wells in hundreds of species of trees and woody vines, but Williamson’s Sapsuckers almost always tap pines or other conifers.
Among North American woodpeckers, Williamson’s Sapsucker is unique in its degree of sexual dimorphism (the difference in appearance between the sexes). In most woodpeckers, males and females differ only in the amount of red or yellow on the head. Male and female Williamson’s are so different that they might be assumed to be different species (in fact, that has happened; see sidebar below).
Fortunately, these birds are not hard to identify once you find them. The male, mostly black with bold accents of white, yellow, and red, is not really similar to any other species. The female, more cryptically patterned in brown, might be confused with a few other things, but the images with this column should provide enough information to make it recognizable.
What to look for
Female color pattern. Brown overall, heavily marked with narrow dark bars on back, wings, and sides.
Female underparts. Black patch on chest and bright yellow center of belly, often hard to see.
Female flight pattern. White rump is noticeable in flight, but unlike other sapsuckers, lacks any white patch in wing.
Male color pattern. Mostly black with white face stripes, white wing patch and rump, yellow belly.
Juveniles. Young birds look very similar to adults of the same sex, so they pose no additional ID challenge.
Williamson’s Sapsucker, adult male. Nothing is really similar to the male Williamson’s Sapsucker. Even other woodpeckers with a lot of black in the plumage, such as Black-backed or Acorn Woodpeckers, are easily separated by a glance at face pattern or wing pattern. Although it looks striking in pictures, the overall dark appearance of this bird helps to make it inconspicuous in the shady coniferous forest where it lives. Incidentally, young juvenile Williamson’s Sapsuckers look very similar to adults of the same sex. Juvenile males have the center of the throat white instead of red, but otherwise they look almost identical to adult males. Likewise, juvenile females look like adult females, but without the black patch in the center of the chest.
Yellow-bellied Sapsucker, juvenile. In three of the four sapsucker species (including Williamson’s), juveniles are essentially finished with molting to first-winter plumage by early fall, before they leave the breeding grounds. However, young Yellow-bellied Sapsuckers complete the molt much later, migrating south while still mostly in juvenile plumage. These young birds might be confused with the female Williamson’s Sapsucker, as they are very brown overall, with buff-brown spangling on the back and some brown barring on the sides. However, even young juvenile Yellow-bellieds show some of the pattern of white stripes on the face. And at all ages they show a major vertical white stripe on the wing; the female Williamson’s is the only sapsucker that lacks this mark.
Williamson’s Sapsucker, adult female. With its muted colors and intensely irregular pattern of markings, this is probably the best-camouflaged woodpecker in North America. Although Williamson’s Sapsuckers will place their nests in the pale-barked trunks of aspen trees, like the one here, they do almost all their feeding on the dark trunks of pines, firs, larches, and other coniferous trees, where the female’s pattern blends in especially well. As seen in the photo on the previous spread, the adult female has a yellow center of the belly and a black patch on the chest — an early name for the species was “Black-breasted Woodpecker” — but these markings are usually hard to see, leaving the bird with few obvious field marks.
Gila Woodpecker, adult female. Sapsuckers are not closely related to the zebra-backed woodpeckers of the genus Melanerpes, such as Red-bellied, Golden-fronted, and Gila Woodpeckers, but the color pattern of the female Williamson’s can suggest those birds. Williamson’s Sapsuckers sometimes show up in the lowlands of the Southwest in fall or winter, and females might be mistaken for the female Gila Woodpecker, which lacks any red on the head. Farther east, they could be confused with juvenile Red-bellied or Golden-fronted Woodpeckers, which lack most color on the head at first. These Melanerpes woodpeckers are more cleanly black and white on the back, and lack heavy barring on the sides. They’re also much more active and noisy than the quiet, furtive sapsuckers.
A double identity
Williamson’s Sapsucker was described to science twice — and for two decades, it was classified as two different species. John Cassin described the female in 1852, based on specimens from California, under the name Picus thyroideus. John Newberry, taking part in an expedition led by Lieutenant Robert Williamson, collected a male in Oregon in 1855 and described it 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.
In 1873, an energetic young naturalist named Henry Henshaw traveled through the Southwest. Among other discoveries, he solved the puzzle of these birds. He wrote: “While in southern Colorado during the past season, I obtained abundant proof of the specific identity of the two birds in question, Williamsonii being the male of thyroideus. Though led to suspect this, from finding the two birds in suspicious proximity, it was some time before I could procure a pair actually mated.” At a nest excavated in the trunk of a live aspen, Henshaw observed both parent birds coming in to feed the young.
The specific name thyroideus has priority because it was published first, so the bird is now officially Sphyrapicus thyroideus. Although the name williamsonii has no scientific status, the English name of Williamson’s Sapsucker is a good second-place prize.