If you’ve ever come across a tree with a row of holes drilled into its bark, you’ve likely seen the handiwork of a Yellow-bellied Sapsucker: true to its name, this boldly patterned woodpecker uses its stout bill to drill holes into the cambium of trees, causing sap to flow out. These holes, called sapwells, are an important resource for many species of animals besides sapsuckers. Insects, bats, squirrels, and even porcupines make use of sap wells, to say nothing of hummingbirds. Hummingbirds have a special relationship with sapsuckers: they time their spring migration so as to arrive when the sapwells have begun to flow. In addition to the sap itself, hummingbirds also feed on insects that are attracted to the sweetness. Hummingbirds can be exceedingly protective of these natural “feeders”, patrolling the choicest trees and chasing off other birds that attempt to feed from them! So many species rely on sapwells for food (about three dozen species of birds alone) that some biologists consider sapsuckers to be a keystone species in woodlands where they are found.

Compiled by Owen Moorhead. Sources include the Cornell Lab of Ornithology and National Audubon Society. Image courtesy of Samantha Pitts via National Audubon Society.

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