The Ecological Importance of the Yellow-Bellied Sapsucker

Image of Yellow-Bellied SapsuckerPhoto: Life Lenses

The Yellow-Bellied Sapsucker, or Sphyrapicus varius, is a medium-sized woodpecker with the ability to drain sap from the trees upon which it feeds. This small bird with a long name has only shared some of its secrets with naturalists.

Description of the Yellow-Bellied Sapsucker

The male Yellow-Bellied Sapsucker has a red “cap” on top of his head, black and white stripes along his cheeks, a white throat, dark wings with white specks, and the pale yellow stomach for which it is named. Females lack the red cap and are generally more muted in shading, but also have yellow bellies.

Adults may grow to about nine inches in length with a wingspan of 16 inches. They tip the scales at about 50 grams.

Habitat and Behaviour of the Yellow-Bellied Sapsucker

These birds live in North American forests, whether in open or dense canopy environments. In the summer they live in a broad band across Canada, from northern British Columbia and south-east through the Great Lakes and into the Maritime provinces. They also summer in the northern United States from the Midwest through to the Eastern Seaboard.

Yellow-Bellied Sapsuckers migrate to the south-eastern United States, Mexico and the West Indies for the winter. Surprisingly, the females travel farther to the south than do the males.

Males choose the breeding grounds: both the general territory and the specific nest site. They also make the largest contribution to hollowing out a cavity in a tree trunk, to serve as the season’s brood nest. This job takes up to a month in the spring.

Yellow-Bellied SapsuckerPhoto: New Jersey Birds

Breeding Habits of the Yellow-Bellied Sapsucker

Two to seven eggs constitutes a clutch. The eggs are incubated for two weeks, with the male sharing in this task.

Once hatched, nestlings are fed sap-drenched insects by both parents. Within a month, the young are encouraged to take flight. Sometimes the parents will entice their children with food held just out of reach from the nest.

Feeding Habits of the Yellow-Bellied Sapsucker

Yellow-Bellied Sapsuckers eat insects, much as do other woodpeckers. Based on the first image, they will also eat seeds or berries.

They gain their name, however, because they also drill for, and consume, the “phloem” sap from trees. This is the nutrient-rich sap that flows down from the leaves towards the roots. Maple syrup is made from the watery “xylem” sap that flows up from the roots in early spring.

Their remarkable drilling technique maximises the flow of phloem sap. By drilling a horizontal row of holes, the first sap leaks out but then thickens and clots, much as does a cut on a human arm. This blocks the downward flow of sap. The Yellow-Bellied Sapsucker then drills a new row just above the old, where the sap is actually under greater pressure since it cannot flow past the self-plugged holes. Eventually a grid of holes can be seen; the top row will be the most recent.

Female Yellow-Bellied SapsuckerPhoto: New Jersey Birds

Ecological Importance of the Yellow-Bellied Sapsucker

Their ability to draw phloem sap from trees makes the Yellow-Bellied Sapsucker an important ally for several other animals that drink tree sap. Among mammals, bats, porcupines and squirrels all appreciate the efforts made by the sapsucker.

Their greatest beneficiaries, however, are hummingbirds. In particular, the ruby-throated hummingbird would be hard pressed to find enough nectar from flowers in the northern edges of its breeding zone. The tree sap released by sapsuckers makes a perfect substitute for nectar.

Male Yellow-Bellied SapsuckerPhoto: Kelly Colgan Azar

References:
Mary Deinlein, National Zoo of the Smithsonian Institute, “Yellow-bellied Sapsucker“, Aug. 2003, referenced Aug. 1, 2011; and “Yellow-bellied Sapsucker Life History“, referenced Aug. 1, 2011.

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