One mid-summer day while out for a walk, I heard a loud buzz and looked up to marvel at a hummingbird moving methodically along the bark of a basswood tree, lapping up sap that oozed from small holes chiseled by a yellow-bellied sapsucker. Although the sapsucker is saddled with a name that sounds like an insult, it plays a critical role in the lives of hummingbirds and many other animals.
Yellow-bellied sapsuckers are bold birds with a sporty plumage. Pastel yellow feathers on the breast are highlighted by a bright red cap and striking zigzag bars of black and white on each side of the head and neck. They also have a white wing stripe and a red neck with a bib-like black crescent.
“Sapsucker” comes from their habit of pecking neat, horizontal rows of holes in tree bark. They’re especially fond of tapping basswood, apple, hemlock, sugar maple, and white birch. As soon as male sapsuckers migrate northward in late March or early April, they start pecking lattice-like patterns of 1/4-inch holes across trunks and branches to tap the sap of the inner bark (phloem) that carries sugar and other nutrients down from the treetops. They periodically clean out and renew the holes to keep the sap flowing.
Unlike sap drawn from the xylem (sapwood), which is tapped in the deeper holes drilled by farmers to make maple syrup and which contains from 2-3 percent sugar, phloem sap may contain 20-30 percent sugar. Sapsuckers use brush-like tongues to lap the sap that accumulates at the top of each hole. Once the flow subsides, sapsuckers move up the bark and start another row of holes. They also eat cambium and inner bark as they chisel.
The mix of sugar and other nutrients contained in the sweet sap is similar to flower nectar, so it’s no surprise that the northernmost range of the ruby-throated hummingbird coincides with the summer breeding territory of the yellow-bellied sapsucker. When hummingbirds arrive in New Hampshire and Vermont in early May, enough sapsucker holes are already exuding sweet sap to supplement the nectar from early-blooming flowers. Hummingbirds continue to feed on sapsucker wells throughout the summer – they even shadow sapsuckers making the rounds of the best sap wells, chasing away other birds (except for sapsuckers) that come to feed.
But the impact of sapsucker activity extends well beyond hummingbirds. Their sap wells are nature’s soda fountains for about three dozen different species of birds, including other woodpeckers, yellow-rumped warblers, Cape May warblers, eastern phoebes, ruby-crowned kinglets, nuthatches, and chickadees. The sap also nourishes a host of mammals and insects, including squirrels, bats, porcupines, and insects from at least 20 different families, such as bees, wasps, hornets, and moths.
Some animals, like red squirrels, feed directly on the sap, while many others, including hummingbirds, also feast on insects drawn to the sweetness. Some fungi colonize the oozing sap, including one called “black bark” that forms dark, canker-like patches. Many bacteria and fungi that can decay and discolor wood enter trees through sapsucker holes.
Studies show that the diversity of many forest species, as well as the size of the population of each species, is greater in areas with high levels of sapsucker activity. Because of this effect, sapsuckers are considered a keystone species –they have a critical impact on the surrounding ecological community that goes beyond what would normally be expected from their numbers. Beavers are another example of a keystone species – their ponds provide critical food, water, and cover for an array of plants and animals.
Late sleepers, however, might describe sapsuckers as more of a hammer-stone species as males bang their notoriously loud “rat-a-tat-tat” territorial calls on metal roofs, chimney caps, and other resonant surfaces. In our region, sapsuckers often chisel nest holes in the punky wood of aging aspens infected with white trunk rot fungus. They also nest in cottonwood, beech, pine, fir, maple, birch, elm, butternut, willow, and alder. Hatchlings call incessantly for adults to bring insect meals, some of which are coated in sweet sap like a bug fondue. Adults feed on tree sap and a smorgasbord of insects, including ants, which comprise up to a third of their diet.
Sapsuckers lap at their sap wells several times a day throughout the growing season. As summer advances and the sap wanes, sapsuckers tap the species of trees that have the best sap flow at any particular time. They also supplement their diet by eating more insects and partaking of ripening berries and nuts. Overall, their signature sap-tapping has a positive influence on the world around them, even as it remains the source of their dubious moniker.
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