Carpenter ants tunnel along the grain inside decaying heartwood. A pileated woodpecker follows those galleries, chiselling with the grain and producing an elongated rectangular or oval opening that can be more than 30 centimetres long and deep enough to weaken a trunk.
The bird is equipped for the work. The skull is reinforced, the neck musculature heavy, and the tongue long, barbed and coated in sticky saliva, wrapping around the back of the skull when retracted. Stiff tail feathers brace the body against the trunk while it strikes.
Those excavations matter beyond the woodpecker. Abandoned pileated cavities are used by owls, ducks, swifts, bats and martens that cannot excavate for themselves, which makes the species a keystone cavity provider. The popular idea that woodpeckers avoid concussion through a shock-absorbing skull is now questioned; recent work suggests the head acts more like a stiff hammer than a cushion.