Friday, April 19, 2024

A male yellow-bellied sapsucker rests in a tree in February. Males and females have a red crown, but only the males have a red throat. (Photo: Richard George)

I was older than I care to admit before I realized that a yellow-bellied sapsucker (Sphyrapicus varius) was an actual bird and not an insult flung around on Saturday morning cartoons. Just saying the term can elicit laughs from an audience.

It turns out that a yellow-bellied sapsucker is a type of woodpecker, and one you can see here in Cambridge. Unlike other woodpeckers, which drum trees rapidly in search of grubs, insects or ants, a sapsucker often pecks a series of holes into trees to create reservoirs called sap wells, into which sap drips. The bird feeds on the thick sap by collecting the sap with its brushlike tongue. Sapsuckers also dip insects in the sap to mop up the sticky delight. The birds visit their sap wells frequently, especially during the late summer and fall when sap is their primary food source. Hummingbirds, squirrels, butterflies, beetles, moths, chipmunks and bats eat the sap when the sapsucker leaves the holes unattended. Very few trees are injured permanently by this process.

A yellow-bellied sapsucker pokes its bill into a tree in Avon Hill in December. (Photo: Richard George)

During nesting season (late spring into the summer), insects make up about half of the sapsucker’s diet, and sapsuckers are one of the most active woodpeckers, darting from tree to tree to collect bugs from bark and leaves. During the winter and spring, they often eat cambrium, which is the membrane just beneath a tree’s bark. From October to February, the birds rely heavily on fruit.

A yellow-bellied sapsucker in Huron Village in April. (Photo: Richard George)

The sap that sapsuckers eat is different from the sap that people collect to make maple syrup. Sapsuckers drill shallow holes, and this sap is thick, containing 20 percent to 30 percent sugar. People who tap maple trees drill deeper, collecting a watery sap that is only 2 percent to 3 percent sugar and flows more easily. (Of course, people can boil it down to make it thicker and higher in sugar content.)

At the end of the summer in September, sapsuckers fly south; in October, migrants from Canada begin arriving in the Northeast. In the summer the birds are noisy and full of energy, but the fall and winter birds are quiet and secretive. Our yellow-bellied sapsuckers winter in the southern United States, the Caribbean or Central America, but Canadian birds may overwinter in the Northeast. Females migrate farther south than males. In Central America in the winter, there are three females for every male.

A female yellow-bellied sapsucker in November. Females have a white throat. (Photo: Richard George)

In the spring, sapsuckers pairs unite to form a breeding. They spend several weeks chipping out a 12-inch-deep nest cavity, wider at the bottom than the top, often in a birch, maple or aspen tree. Then the female lays about five or six eggs, which she incubates during the day for two weeks; the male takes over night incubation duties. After the chicks hatch, the doting parents offer newborn chicks small insects. As the chicks grow over the next roughly 40 days, they get increasingly larger ones from their parents. After the chicks fledge, they still rely on insects from the parents; but supplement the insect diet with sap from the parent’s sap wells.

The belly of a yellow-bellied sapsucker may indeed be tinged yellow, as seen on this bird in Huron Village in February 2022 – but sometimes the yellow tinge is absent. (Photo: Richard George)

Because sapsucker nest cavities are large, other species use their holes for refuge or nesting sites. Often sapsuckers return in the spring only to find that their nest cavity from the previous season has been claimed by a squirrel or an owl. John James Audubon wrote about an eastern screech owl that was surprised when yellow-bellied sapsuckers reclaimed their nesting site:

I was much surprised to see a pair of [yellow-bellied-sapsuckers] disputing the entrance of a hole with an Owl (Strix asio), which for nearly a quarter of an hour tried, but in vain, to drive them away from its retreat. The Owl alighted sidewise on the tree under its hole, swelled out its plumage, blew and hissed with all its might; but the two Woodpeckers so guarded the entrance with their sharp bills, their eyes flushed, and the feathers of their heads erected, that the owner of the abode was at length forced to relinquish his claims.

A yellow-bellied sapsucker checks its sap wells in Huron Village in February 2022. (Photo: Richard George)

A yellow-bellied sapsucker checks its sap wells in March 2021. (Photo: Richard George)

Yellow-bellied sapsuckers play an important role in local ecosystems. They uncover beneficial sap and hollow out tree cavities, which provide food and shelter for other species. In fact, scientists have learned that ruby-throated hummingbirds time their northern migration to coincide with that of the yellow-bellied sapsucker. These hummingbirds do not breed until the yellow-bellied sapsucker has created sap wells, a chief source of spring food for these birds. In fact, ruby-throated hummingbirds often build their nests close to the yellow belly’s sap wells. Sap wells also provide important food repositories for butterflies, beetles, moths and flies. Yellow-bellied sapsuckers improve an ecosystem’s biodiversity because their presence increases the number of insects, which is good news for hungry birds, reptiles and small mammals.



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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.