The feeding strategy of woodpeckers requires two specialized adaptations, one of which is known to all bird enthusiasts and the other of which is only known to a small number of them.
When constructing a nest cavity or searching for tasty beetle grubs, the first skill is the ability to hammer into wood and discard the chips. The head of the woodpecker strikes the ground with at least 1,000 times the force of gravity (1,000 g), but the bird appears unharmed. In contrast, a 100 g impact on a human would undoubtedly cause death. Why then do woodpeckers not suffer from headaches or brain damage?
The bird’s ability to absorb shock is influenced by a number of factors. One is a chisel-like, self-sharpening beak that moves into wood rather than coming to a sudden stop. (See the example above.) Strong neck muscles are another. The brain doesn’t slosh around as much when there is less room in the skull. Additionally, since it allows the force to be dispersed over a larger surface area, the orientation of the brain itself is crucial.
Researchers studied Great Spotted Woodpeckers
Recent research on Great Spotted Woodpeckers was conducted by Beihang University researchers in Beijing, China using high-speed cameras, torque sensors, and scanning electronic microscopy. They found small changes in the bone structure in the bird’s lower mandible and parts of its skull that allow sliding (deformation), which lessens the force of pecks. They also discovered that the woodpecker’s lower beak’s boney structure was longer than its upper beak’s tissue layer and that the upper beak’s tissue layer was longer than the lower beak’s layer. Because of this mismatch, energy can be directed through the lower beak and away from the braincase, according to the researchers.
The second adaptation is an unusually long tongue. Since a woodpecker typically probes crevices that prevent us from seeing the tongue, its length is one of the best-kept secrets of birdlore. Our best opportunity to see a woodpecker’s tongue is when a flicker feeds on ants at an anthill.
Woodpeckers are omnivores that feed on insects, spiders, and other arthropods, as well as nuts, fleshy fruits, and sap. A specialized tongue isn’t needed to eat nuts and other fruit, but it’s a great adaptation for reaching into narrow openings to extract tasty morsels. This is especially true when a woodpecker taps into an ant run or an insect gallery.
Woodpecker tongues vary, but most are long and narrow and have an assortment of backward-projecting barbs near the tip. A woodpecker sometimes uses its tongue as a spear, penetrating and then dragging insects to the surface, but the bird probably uses it more often as a rake, extending it into holes and then retracting it. Woodpeckers also produce large amounts of sticky saliva that coats the tongue, enhancing their ability to capture insects.
A complex of cartilage and bone called the hyoid apparatus supports the tongues of all vertebrates. In birds, the small hyoid bones and cartilage extend to the tip of the tongue.
Two horns of the hyoid, each consisting of narrow bones and cartilage, project backward and laterally from the base of the tongue. In most birds, the horns of the hyoid terminate on either side of the trachea, but in woodpeckers they continue farther back. Muscles attached to the hyoid move the tongue; when the hyoid apparatus is moved forward, the tongue is extended. The greater the length of the hyoid horns, the farther the tongue can be extended. The tongue can be several times longer than the bill.
Storing a long tongue
A problem with a long tongue is where to store it when it’s not in use. Woodpeckers came up with a creative solution. Rather than terminate below the skull, the hyoid horns continue over the back of the skull, just under the skin, and continue over the top of the skull. The two horns then join, extending forward as necessary — sometimes inserting into the right nostril.
Downy, Hairy, Red-bellied, and Red-headed Woodpeckers all feed on insects and other organisms, as well as fruit. The birds’ tongues are intermediate in length and have varying numbers of barbs.
Flickers, which likely eat more ants than any other North American bird, have a flattened tongue with few barbs and rely on sticky saliva to capture insects. Flickers have the longest tongue of our woodpeckers and commonly visit anthills, where they move their tongue in snake-like fashion over the surface.
Surprisingly, Pileated Woodpeckers have a relatively short tongue. They typically excavate deeply into trees, looking for insects — especially carpenter ants, which the big birds seem to relish. Sapsuckers have the most unusual tongue of all woodpeckers: it’s short and terminates with brush-like bristles that are adapted for feeding on sap. The bristles absorb sap through capillary action.
Sapsuckers typically drill neat rows of closely packed tiny wells, often a quarter-inch in diameter. Besides sap, the birds feed on insects, and especially relish those attracted to the sap wells.
Adaptations to prevent brain damage from a life of hark knocks serve woodpeckers well, and their long tongues permit the capture of hidden morsels of food. The clever adaptations are further examples of the amazing lives of birds.