In March we welcome the first signs of spring—early blooming crocus, spring peepers, wave after wave of Snow Geese heading to Arctic nesting grounds. Below the surface, warming days and cool nights awaken the tissues of trees causing the sap stored deep in the roots to rise. Spring sap is drawn upward like a sponge through a tree’s sapwood layer, or xylem, to feed newly emerging leaves and flowers. Tree sap is mostly water with some minerals and sugar in the mix; the perfect cocktail to promote tree growth. Spring sap is very similar in content to flower nectar and—to our great benefit—can be tapped and processed into scrumptious maple syrup.
But tapping rising sap in spring is not limited to human ingenuity. Birds of the genus Sphyrapicus—the sapsuckers—are the original artisans of sap-tapping. The 4 species of sapsuckers endemic to North America seem to time their arrival on summer range with the rise of spring sap. These specialized members of the woodpecker guild actually “farm” live trees for sap, drilling and maintaining sap wells and collecting the trickling sap as skillfully as any maple syrup producer in the Northwoods.
Our 4 North American sapsuckers are the Williamson’s, Red-breasted, Yellow-bellied, and Red-naped. Their genus name, Sphyrapicus (sphyra = hammer + picus = woodpecker) tips us off that they have most Picidae tools of the trade: a stout bill that chisels, hammers, and excavates wood; a concussion-resistant skull; a retractable tongue to extract wood-boring insects; zygodactyl feet (two toes facing forward, two facing back) for gripping vertical tree trunks; a stiff-feathered tail to prop up against tree trunks; and a habit of drumming on objects as a means of communication.
Sapsuckers’ feeding method is unique among woodpeckers. In spring, they drill deep wells into a tree’s xylem layer to feed on sap flowing upward to budding branches. After leaf-out, sapsuckers chisel out shallow, rectangular wells in the tree’s phloem, the layer that transports nutrient-laden sap downward from leaves. The shallow holes collect the oozing sap to form “sap wells.” Sapsuckers make the rounds to feed on the sap with their specialized tongue, which is edged with tiny hair-like projections that hold the sap, much like a paintbrush holds paint. “Sapsipper” would be a more fitting name for this group than “sapsucker.”
Sap wells must be continually maintained with fresh excavations to keep the sap flowing, leaving a distinctive rectangular tattoo of neatly-spaced holes in the tree bark. Sapsuckers are known to feed on over 400 species of hardwoods and conifers, but favor diseased trees and species with high sugar concentrations in their sap, such as paper birch, yellow birch, sugar maple, red maple, and hickory.
Because sap is the lifeblood of a tree, any wound is quickly healed over to stanch the loss of sap. So how do sapsuckers so effectively overcome a tree’s defenses to keep the sap spigot flowing? Sapsuckers continue to stump the scientists; researchers have attempted to duplicate the wounding techniques and patterns of sapsuckers, but were unable to induce sap flow from same or similar trees. One study suggested that sapsuckers have some method to keep sap wells open, such as an anti-coagulant in their saliva or mechanical abrasion using their specialized tongue.
A Keystone Species
Keystone species are those whose removal from a community would hasten a further reduction in species diversity or produce other significant changes in community structure and dynamics. Sapsuckers are considered a “double keystone species” for their two distinct keystone roles. They drill sap wells that nourish a host of insects, birds, and mammals, and they excavate nest cavities required by secondary cavity-nesting birds, such as bluebirds, swallows, and chickadees, and mammals like the Northern Flying Squirrel.
Sap-loving insects from ~20 different families feed at sapsucker wells, including butterflies, moths, bees, wasps, and hornets. Mammals such as squirrels, chipmunks, bats, porcupine, readily feed on the sap. And about 35 species of birds are verified sap robbers, including other woodpeckers, Yellow-rumped, Orange-crowned, and Cape May warblers, Eastern Phoebe, Ruby-crowned Kinglet, orioles, nuthatches, chickadees, and hummingbirds. Most of these birds and mammals (and sapsuckers themselves) will also feast on the many insects drawn to the sap wells.
Sapsucker-Hummingbird Alliance
Back in 1891, a scientist named Frank Bolles noted that hummingbirds fed at sapsucker holes more frequently than other birds, especially in the early spring. Since then, ornithologists have learned that Ruby-throated Hummingbirds time their spring migration in parts of Canada to the arrival of Yellow-bellied Sapsuckers and the ready supply of sweet sap which makes a perfect nectar substitute for hummers when flowers are still scarce. Scientists have observed that the northern limit of Ruby-throated and possibly Rufous hummingbird breeding ranges coincide with the summer breeding range of the Yellow-bellied Sapsucker. The relationship isn’t all one-sided: as hummingbirds make the summer rounds to the best sap wells, they chase away other sap-robbing birds, thereby conserving the precious food resource for sapsuckers (and, of course, themselves).
An excellent video, but if strapped for time, watch the first 2 minutes, then skip to 5:15 and 7:50.
The Sapsucker Species
Finally, here are brief overviews of the 4 sapsucker species of North America, but I invite you to click on the All About Birds (Cornell Lab) linked headers for deeper dives. Of the 4 species, 3 (Williamson’s, Red-breasted, Red-naped) are birds of the western half of the continent, while the Yellow-bellied Sapsucker is the most widespread, generally occurring east of the Rocky Mountains. The Red-breasted and Red-naped sapsuckers were once considered races of Yellow-bellied Sapsucker, but in 1983 were split into 3 distinct species based on distribution, ecology, plumage, mating, and genetics. These 3 species will interbreed where their ranges overlap, and birds with intermediate plumage are often reported.
All 4 species have a slow and irregular drumming pattern reminiscent of someone tapping out Morse code. Their calls are all slightly different, but are variably described as a scratchy, whiny mew or waa, a harsh squeal, raspy chatter, and in the case of the Williamson’s Sapsucker, a high, nasal chyaah that sounds remarkably like a raptor.
Williamson’s Sapsucker
Appearance: A medium-sized bird; males have a black back, white wing patch, white rump, bright red throat, black breast and yellow belly; black head has 2 white facial stripes; females have a brown head, fine horizontal dark brown and white barring on back and wings, white rump, and black breast patch.
Distribution/habitat: Uncommon woodpecker of western mountains and dry conifer forests. Migrates south along mountain ranges in fall as far south as west-central Mexico, or to lower elevations in California.
Fun Facts:
- The female Williamson’s was once considered a different species by early naturalists. By 1873, ornithologists realized they were sexually dimorphic members of the same species.
- Observations by early ornithologists noted Williamson’s Sapsuckers using sap wells in aspen trees; however, observers in the last century report their sap wells solely in conifers, suggesting the early reports may have been Williamson’s robbing sap from wells created by Red-naped Sapsuckers.
Red-breasted Sapsucker
Appearance: Medium-sized bird with red head, nape and breast, white rump, white patch in front of eye, large white wing patch, black back lightly spotted with white or yellow, pale yellow belly, sexes look alike.
Distribution/habitat: Breeds from SE Alaska and British Columbia south along the Pacific coast to S. California. The least migratory of sapsuckers due to relatively temperate climate. Breeds in coniferous forests with a mix of deciduous aspen, alder, and willow.
Fun facts:
- The Red-breasted is the brightest red of North America’s 4 sapsucker species, following an east-to-west pattern of increasing red plumage.
- The Rufous Hummingbird is closely allied with the Red-breasted Sapsucker, nesting near sap wells and shadowing the sapsucker during the day to feed at wells the sapsucker maintains.
Great example of sapsucker drumming in this video.
Yellow-bellied Sapsucker
Appearance: Medium-sized bird with pale yellow underparts and bib-like black crescent at neck; bright red cap, red chin, and throat in male; striking zigzag black and white bars on sides of head and neck; white rump, blackish back, and large white wing patch.
Distribution/habitat: Highly migratory – the “jet setter” of the woodpecker clan; breeding range is mixed coniferous/deciduous forests across Canada and NE United States; during migration, passes through all areas east of the Rockies; winters in SE U.S. southward into Mexico, Central America, and West Indies.
Fun facts:
- Female Yellow-bellieds migrate farther south than males, with females comprising ~75% of the overwintering population in Mexico, Central America, or the West Indies. This may be related to springtime pressure on males to get to breeding grounds ASAP to establish territories.
- The Yellow-bellied Sapsucker often uses human infrastructure to amplify its territorial drumming. Surfaces like metal roofs, rain gutters, chimney caps, metal trash cans, street signs, or satellite dishes all resonate loudly to proclaim a territory.
Excellent sap drinking footage in this video + mouthfuls of flying insects!
Red-naped Sapsucker
Appearance: Medium-sized woodpecker with red forecrown and nape patch on black and white head; chin and throat red in male; females have small white chin patch; pale yellow underparts with spotted sides, black breast band, white wing patches; red nape patch distinguishes this species from Yellow-bellied Sapsuckers in the East and Red-breasted Sapsuckers in western coastal states.
Distribution/habitat: Breeds in the Rocky Mountains from SW Canada south to CA, AZ, and NM; short-distance migrant to SW U.S. and Mexico; summer range is deciduous and coniferous forests with a mix of willow, aspen, birch, ponderosa pine, juniper, or Douglas-fir trees up to 10,000 ft. elevation.
Fun facts:
- Rufous, Calliope, and Broad-tailed hummingbirds follow Red-naped Sapsuckers around, stealing sips of sweet sap and picking off arthropods mired in the ooze.
- Courting Red-naped Sapsuckers face each other with bills raised, red throat feathers puffed out, and crown feathers erect while swinging their bills from side to side.
Excellent quality video showcasing Red-naped Sapsucker calls and excavation.
Which sapsuckers live in your part of the country?
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