Woodpeckers are instantly recognizable by their characteristic behavior of striking wood with rapid, powerful blows, an action known as pecking. This behavior is not random or destructive, but a set of specialized, biologically driven activities that allow these birds to thrive. The precise reasons for pecking determine the type of hole created, serving multiple purposes related to foraging, communication, and shelter-seeking.
Excavating for Food
The primary reason a woodpecker drills is to access a protein-rich diet of insects and their larvae hidden within the wood. Woodpeckers typically target dead or decaying trees where wood-boring beetles, ants, and other invertebrates have established galleries beneath the bark. The birds use auditory cues, listening for the faint sounds of insects moving, before concentrating their pecking to expose the prey. Once a cavity is opened, the woodpecker uses its specialized, long, barbed tongue to probe deep into the tunnels and extract the meal.
The holes created during foraging are generally irregular in shape and depth, reflecting the search pattern for insect tunnels. An exception is the sapsucker, a type of woodpecker that drills to consume tree sap. Sapsuckers create orderly, closely spaced rows of shallow holes in living trees, allowing the sugary liquid to flow out. The birds return repeatedly to these “sap wells” to lap up the sap and any small insects trapped in the fluid, leaving a distinctive pattern on the trunk.
Creating Nests and Roosts
Woodpeckers are primary cavity excavators, meaning they create their own holes for shelter and reproduction, unlike secondary users who occupy existing spaces. These excavated cavities serve as secure nest sites for laying eggs and raising young during the breeding season. The deep chambers protect the clutch from predators and the elements, often featuring a narrowed entrance tunnel leading to a wider, vertical chamber.
Beyond nesting, these holes provide safe, warm overnight roosting spots, which are important during colder months. A roosting cavity can be up to 18 degrees warmer than the outside air, helping the bird conserve energy. Most species excavate a new nest cavity each year, though they may reuse old roosting holes for several seasons. The abandoned cavities remain a lasting resource for the ecosystem, adopted by more than 35 species of secondary cavity users, including small owls, flying squirrels, and chickadees.
The Science of the Head
The woodpecker’s ability to withstand repeated, high-impact blows without brain injury has long been studied. The bird’s brain is small and fits tightly within the skull, minimizing movement upon impact. Research suggests the head functions as a rigid hammer to enhance pecking efficiency rather than a shock-absorbing damper. This rigidity allows force to be transmitted effectively through the beak to the wood.
A complex set of anatomical features manages the impact forces, which can reach decelerations of up to 400 times the force of gravity. The specialized hyoid bone, which anchors the tongue, is a long, flexible structure that wraps around the skull, possibly acting as a restraint or brace. The bird’s beak is also designed with an unequal length between the upper and lower mandibles, which helps distribute the force away from the brain. The direct, linear trajectory of the pecking motion prevents the rotational forces that are most damaging.
When Woodpeckers Attack Structures
Woodpeckers sometimes direct their pecking toward man-made structures like siding, trim boards, or utility poles, leading to conflict with homeowners. The reasons are the same as in the forest, but the birds mistake the material for a suitable natural substrate. They may be foraging for insects, such as carpenter bee larvae, resulting in small, irregular holes.
A second common reason is “drumming,” a non-vocal communication used to attract mates or proclaim territory, which occurs in the spring. Woodpeckers select resonant surfaces, such as metal gutters or hollow siding, because they amplify the sound. Finally, a woodpecker may attempt to excavate a large nesting or roosting cavity in the side of a house, which causes the most significant structural damage. Deterrence methods focus on non-lethal persuasion, such as eliminating insect infestation, using visual deterrents like reflective tape, or covering the area with netting.