Shades of Green: Earth's Forests -- Woodpeckers

Woodpeckers are perfectly adapted for life in the forest. There are many different species, most of which can be found throughout North America's temperate forests in all seasons. Often they are heard, rather than seen. Using their thick, powerful beaks, woodpeckers busily hammer out notches in tree trunks as they search for wood-boring insects.
Most of these birds have feet with two toes pointing forwards and two pointing backwards, which make it easy to grip onto vertical tree trunks. Their tails are short and stiff, and can be used as props when pressed against a tree. With these special adaptations, woodpeckers are extremely efficient at finding and capturing their insect prey.

Holes drilled by a woodpecker in a "wildlife tree". Photo by Maya Walters

A pileated woodpecker foraging among conifers. Photo by Maya Walters

When foraging, woodpeckers perch on tree trunks and listen carefully for the sound of an unsuspecting insect moving just under the bark. When an insect is detected, the woodpecker quickly drills into the bark and uses its long tongue to extract its prey. Most woodpeckers are just as likely to hunt for insects on coniferous trees as on deciduous trees. Several species do prefer to forage on standing dead trees, where there are always large numbers of wood-boring insects.

Not only do woodpeckers help the forest by consuming many pests such as bark beetles, they also provide essential nesting holes for other animals. These holes created by foraging woodpeckers are especially important to songbirds, and they are constantly in demand for nesting sites. Red squirrels and flying squirrels also compete for the use of these holes. Unfortunately, humans often remove the standing dead trees in a forest, which are the trees that contain the largest numbers of these notches.

However, not all woodpeckers forage for insects in the same way. Some species lack the stiff tail that allows others to perch vertically on the trunks of trees. The wryneck woodpecker is one of these species that does not climb; instead it descends to the ground to feed from ant nests, and can catch more than 100 ants with a single flick of its long tongue.

Left: Woodpecker holes on a living conifer. Photo by Maya Walters. Below: A yellow bellied sapsucker perched in a thicket of bushes and trees. Photo courtesy Pam Hawkins.

The sapsucker woodpeckers have their own ingenious trick for catching insects. They do drill holes in trees like other woodpeckers, but only in trees that are living and producing sap. Sapsuckers create numerous small, squarish holes in such trees and allow the sap to begin dripping out. This sweet liquid attracts insects, which become trapped, and the woodpeckers then eat both the insects and the sap together.

Other woodpeckers don't feed on insects at all. Acorn woodpeckers, quite predictably, feed on acorns. They drill holes into trees, not to catch insects, but to store nuts. They can cache hundreds of acorns within numerous small holes in a single tree. These more unusual feeding habits, however, are practiced only by the minority of woodpecker species.

Woodpeckers also excavate holes especially for their own nests, and they take more care with their nesting holes than with their foraging holes. They usually nest in dead trees, and manage to chip holes out quietly to avoid being noticed by potential predators. In certain areas, woodpeckers have developed very elaborate nesting procedures to deal with particular characteristics of a forest.

Carpenter ants and other insects that woodpeckers feed on live within tunnels in dead standing trees. Photo by Maya Walters.

Small fires occur frequently in southern coniferous forests, and woodpeckers there nest in living trees, which don't burn as easily as dead trees, and therefore offer more protection. However, these living trees exude a thick, strong-smelling sap through any wounds in the outer layers of their trunks. This prevents the birds from making satisfactory nests. These woodpeckers are forced to move lower down to a thicker area of the trunk, where there is sufficient nesting space below the outer sap-producing layer of wood. Nesting lower down means they are more vulnerable to predators such as snakes, which can actually climb the tree trunks to steal chicks from the nests. The woodpeckers protect their young from these threats by drilling small holes all around the nest entrance, which then exude sap onto the trunk. This sap prevents anything from climbing up to the nest. These specialized foraging and nesting techniques have been developing over thousands of years.

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