Woodpeckers: 2

 

(This Buffalo News column was first published on January 22, 1996.)

 

      Most of us have had the unfortunate experience ‹ usually in the dark ‹ of walking into a wall.  It is not a pleasant misadventure.  Thankfully, few ‹ at least of those who live to tell of it ‹ have run full tilt into a tree.

 

      Yet that is what a woodpecker does hundreds of times each day.  It pulls its head back as far as it can and then thrusts it forward in a straight trajectory, its eyes closing an instant before striking.  The bill hits solid wood at about 15 miles per hour.  That is not very fast compared to automobile speeds, but it is the velocity of a runnerąs four-minute mile.

 

      Why donąt woodpeckers suffer terrible headaches?  The answer is complex.  First and most important, they enjoy the advantage of smaller size.  Their lesser mass-to-surface ratio makes the deceleration force at impact correspondingly less.  This is the same property that allows an ant to fall from a table top to the floor with no ill effect.  The antąs drop is proportional to that of a human falling from the top of City Hall, but size is on the smaller animaląs side.

 

      Like those of all birds, woodpeckersą brains are even smaller than their body size relative to humans, thus adding to this advantage.  This difference alone makes them 50 to 100 times less vulnerable to brain trauma.

 

      Size is not enough, however, and woodpeckers also enjoy physiological adaptations that allow them to use their heads and bills as pickaxes.  Their brains are not in line with their bills; thus the strongest collision forces are transmitted to bones below the brain.  Tough brain casings and associated muscles act as shock absorbers.  Also there is less fluid in and around their brains than in ours, reducing the damaging shock waves that we suffer in accidents.  Finally, some of the shock is diverted by their bills being held slightly open at impact.

 

      A less obvious feature of woodpeckers is their tongue.  Like that of frogs and anteaters, it is very long but it differs significantly in structure.  The cartilage supporting a woodpeckerąs tongue is coiled down into the throat and from there up over the top of the skull.  In some species it is finally attached to the bill, in others it is wound around the eye socket.  Straightening this lengthy coil extends their tongue well beyond the end of their beak.

 

      Most woodpeckersą tongues are sharply pointed and barbed, helping them to reach deep into crevices for boring insects.  Their salivary glands secrete a glue-like fluid on the ends of their tongues that also helps to hold prey.  These glands are especially well developed in flickers, which probe anthills to feed on those colonial insects.

 

      Unlike their relatives, sapsuckers have tongues with brush-like tufts appropriate to their sap-drinking habits.

 

      Woodpeckers also enjoy special adaptations to their lives clinging to tree trunks.  Stiff tail feathers give them a tripod-like prop and well-developed claws a firm grasp on even the smooth surfaces of beech and birch trees.  As should be expected, in most species all four toes are well developed and they are directed at right angles, thus providing excellent stability.  This is especially important because woodpeckers do not walk but leap from one position to the next, sometimes even doing this on the bottom side of branches.  (The more sedentary three-toed woodpeckers lack the rear toe.)

 

      Finally, the especially tough skin of woodpeckers protects them against the stinging insects they meet in foraging.

 

      Woodpeckers are surely among the most remarkably adapted of all wildlife.