The “woodpecker niche” is based on digging holes in live wood and on prying off pieces of bark. That means dependable food sources all year round in the form of sap, insects living under bark, and insects burrowing into wood. It also means an excellent place for a nest, since a hole in a tree affords protection from wind, rain, predators, and temperature fluctuations. Other bird species besides woodpeckers can pull off the easier feat of digging nest holes in dead wood, but there are many fewer dead trees than live trees available.
…woodpeckers are very successful birds. There are nearly two hundred species, many of them common. They come in all sizes, from tiny birds the size of kinglets up to crow-sized. They are widespread over most of the world, except on oceanic islands too remote for them to reach by flying.
Woodpeckers are not an extremely distinctive old group without close relatives, like egg-laying mammals. Instead, ornithologists have agreed for a long time that their closest relatives are honey guides, toucans, and barbets, to which woodpeckers are fairly similar except in their special adaptations for woodpecking. Woodpeckers have numerous such adaptations…
First and most obvious are the adaptations for drilling in live wood. These include a chisel-like bill, nostrils protected with feathers to keep out sawdust, a thick skull, strong head and neck muscles, and a hinge between the base of the bill and the front of the skull to help spread the shock of pounding. Many other birds, such as parrots, peck or bite holes in dead wood. Within the woodpecker family there is a gradation of drilling ability – from wrynecks, which can’t excavate at all, to the many woodpeckers that drill in softer wood, to hardwood specialists like sapsuckers.
Another set of adaptations are those for perching vertically on bark, such as a stiff tail to press against bark as a brace, strong muscles for manipulating the tail, short legs, and long, curved toes. The evolution of these adaptations can be traced even more easily than can the adaptations for woodpecking. Even within the woodpecker family, wrynecks and piculets do not have stiff tails for use as braces. Many birds outside the woodpecker family, including creepers and pygmy parrots, do have stiff tails that they evolved to prop themselves on bark.
The third adaptation is an extremely long and extensible tongue, fully as long as our own tongues in some woodpeckers. Once a woodpecker has broken into the tunnel system of wood-dwelling insects at one point, the bird uses its tongue to lick out many branches of the system without having to drill a new hole for each branch. Woodpeckers’ tongues have many animal precedents, including the similarly long insect-catching tongues of frogs, anteaters, and aardvarks.
Finally, woodpecker have tough skins to withstand insect bites plus the stresses from pounding and from strong muscles. Anyone who has skinned and stuffed birds knows that some birds have much tougher skins than others. Taxidermists groan when given a pigeon, whose paper-thin skin tears almost as soon as you look at it, but smile when given a woodpecker, hawk, or parrot.
This is an excerpt from the book “The Rise and Fall of the Third Chimpanzee” by Jared Diamond. In the chapter “Alone in a Crowded Universe”, Mr. Diamond brought the reference of the “woodpecking niche” to illustrate why sending radio signal to the universe may not yield result to find extraterrestrial life. One must not miss this book to understand the evolution of the third chimpanzee which is homo sapiens.