Yellow-bellied Sapsuckers

Today’s column is about a jazz drummer with a sweet tooth. No, we’re not talking about Gene Krupa. The drummer is one of our more unusual woodpeckers, the Yellow-bellied Sapsucker.

The sapsucker is named for its habit of creating shallow holes, called sap wells, in the bark of trees. The sap that oozes into the wells provides food for the sapsuckers. The sap is a fluid carried in phloem cells of the tree, just beneath the bark. This fluid is rich in organic nutrients, particularly the sucrose (table sugar). These compounds are created in the leaves of the tree by the process of photosynthesis and then carried through the phloem to all parts of the tree. The phloem is essentially a circulatory system for the plant, carrying sugar to parts of the tree that cannot photosynthesize and hence make their own food. In the summer, 25% of the phloem sap is sugar. That’s a sweet treat!

The sapsucker is a bit like a vampire, exposing the phloem cells and drinking the sucrose that oozes out. Unlike most woodpeckers, a sapsucker has a tongue that is brush-tipped, just the ticket for lapping up sap.

The sap wells in the phloem are usually rectangular in shape. I expect you have seen these sap wells before, arranged in neat rows parallel to the ground. A sapsucker tends the sap wells daily, making sure they to ooze sugar by enlarging the area of the well.

In the early spring before the trees have started to photosynthesize, the sapsuckers make holes in a different kind of circulatory system of the plants, the xylem. The main role of the xylem is to transport water from the roots to the aboveground parts of the tree but does contain a little sugar. The sugar in the xylem gets the sapsuckers through the latter part of the spring until the trees start to photosynthesize. The xylem wells are circular in shape and are not enlarged through time.

Over 1,000 species of trees may be used by sapsuckers across their geographic range. In Maine, sapsuckers are usually found in early-growth forests rather than mature, climax forests. Quaking Aspen, Paper Birch and Red Maple are commonly used for the creation of sap wells.

Sapsuckers will use apple trees for the creation of sap wells, causing orchard growers concern about the health of their trees. However, sapsuckers do not generally cause serious direct harm to trees, although the wells may encourage the arrival of insects that are harmful.

The dependence of sapsuckers on the phloem and xylem of birds requires sapsuckers to be migratory. Their breeding range spans the lower half of Canada, New England, Michigan, Wisconsin, Minnesota and North Dakota. The xylem and phloem of trees in these regions are frozen solid during the winter. So, the Yellow-bellied Sapsuckers withdraw to the southeastern and Gulf states into Central America for the winter. We see our first sapsuckers each spring about the middle of April.

Despite the efforts of a sapsucker to ward off other birds from its wells, many birds do take advantage of the sugar in the sap wells or the insects attracted to the sugar. Ruby-throated Hummingbirds seem to have a particularly close relationship. A female hummingbird often builds her nest close to sap wells and follows sapsuckers during the days, as they work their “trap lines”. Some ornithologists have noted that the migration of Ruby-throated Hummingbirds is closely linked to the migration of sapsuckers.

Sapsuckers do supplement their diet with insects. Foraging for insects is particularly important when parents are feeding nestlings. The young sapsuckers need protein to grow. A sugar diet alone is not sufficient for their proper development. Even so, adult sapsuckers have been seen to capture an insect and then dip it into a sap well before feeding the insect to a chick.

Most woodpeckers drum on resonating surfaces as a means of communication. Sapsuckers have an unusual, syncopated style to their drumming. A typical drum usually starts with several rapid strikes, often increasing in frequency, as an introductory roll. Then, after a brief pause, the sapsucker will strike in a slower, less regular cadence.

Like a jazz musician, sapsuckers improvise. No two drums are alike, even from the same bird.

The sapsuckers are particular about the type of tree they use for their drumming, using the trees that produce the loudest noises of the trees available. The trees chosen also yield the lowest sound frequencies. Lower-pitched sounds carry better in a closed forest habitat than higher-pitched sounds.

Most of the sapsucker drumming you hear comes from males although females also drum. Female drums are briefer and softer than the male drums.

[Originally published on June 2, 2007]