Woodpeckers belong to the family Picidae, which includes sapsuckers and piculets. They are found globally in forested regions, excluding Australia, New Guinea, and polar extremes. The common misconception is that woodpeckers consume the wood they peck. However, the true diet of most woodpeckers consists of high-protein sources like insects and various plant materials, not the cellulose and lignin that make up tree trunks. Their distinctive, forceful strikes against trees serve multiple purposes, whether that end is a meal, a home, or a mate.
The Woodpecker’s True Diet
Woodpeckers are primarily insectivores, with insects and their larvae forming the bulk of their diet. They are highly specialized predators that target invertebrates living beneath the bark or deep within the wood, such as wood-boring beetle grubs, ants, and caterpillars. The birds use their acute sense of hearing to detect the movement of these pests inside the timber before beginning to drill.
Once a larva is located, the bird hammers a hole to expose the tunnel, then relies on its unique anatomy to extract the prey. The woodpecker’s tongue is exceptionally long, often extending well past the tip of its bill. It is covered in a sticky substance with a barbed tip, functioning like a spear or rake to snag the insects. The tongue’s extensibility is made possible by the hyoid apparatus, a set of bones that wraps around the back of the skull.
The consumption of wood-boring insects provides a significant benefit to the forest ecosystem by controlling pest populations. For example, some species can remove up to 85% of emerald ash borer larvae from individual ash trees. Woodpeckers are opportunistic feeders and will also consume spiders, seeds, and the eggs and nestlings of other birds when available.
Why Woodpeckers Drill and Drum
Woodpeckers strike wood for different reasons, with the action falling into three main categories: foraging, nesting, and communication. The irregular, focused pecking that causes significant damage is typically associated with foraging. The bird excavates deep into the wood to reach its insect prey, which requires drilling to penetrate the tree’s defenses and access hidden larval tunnels.
Another reason for drilling is the excavation of nesting and roosting cavities, which are essential for shelter and reproduction. These holes are typically much larger than foraging holes and are found in dead or dying trees where the wood is softer. Woodpeckers do not bring in materials to line these cavities; instead, they leave a bed of wood chips from the excavation process.
The third behavior is “drumming,” a rhythmic, rapid striking that is distinct from the slower pattern of feeding. Drumming is a form of non-vocal communication, used primarily to attract a mate and establish territorial boundaries. Woodpeckers choose highly resonant surfaces like hollow trees, gutters, or metal poles to amplify the sound, with some species able to strike the surface up to 17 times per second.
Specialized Feeding Strategies
While most woodpeckers focus on insects, some species have developed highly specialized feeding strategies that incorporate other food sources. The sapsuckers, for instance, rely heavily on tree sap as a primary part of their diet. They drill neat, shallow rows of holes, known as sap wells, just deep enough to reach the phloem, the tissue that transports sugary liquid.
Sapsuckers use their brush-tipped tongues to lap up the sap that oozes from these wells. The wells also serve as an insect trap, attracting ants and other small arthropods that become stuck in the sticky fluid. This provides the bird with a convenient protein source alongside the sugar.
The Acorn Woodpecker exhibits a completely different specialization, focusing on caching nuts for year-round survival. Acorn Woodpeckers drill hundreds or even thousands of specific holes in a single tree, known as a granary tree, for the purpose of storing acorns. They meticulously wedge one nut into each hole, creating a massive, communal food store that ensures a reliable supply during periods when insects are scarce. Many woodpeckers also incorporate soft foods like fruits and berries into their diet seasonally, allowing them to thrive when their primary insect prey is less available.