There are approximately 240 species of woodpeckers in the world, distributed in a variety of habitats across the world, excepting Australasia and Antarctica. Although they make oral sounds- calling- they use drumming – pecking rapidly at a tree, post, metal chimney – to defend their territories. There is an excellent article, Evolutionary and Biomechanical Basis of Drumming Behavior in Woodpeckers, that examines the evolution of drumming behavior and the adaptations the birds have for such behavior.
One would think that since woodpeckers also call, that drumming would be controlled by a different part of the brain rather than the one that controls the vocal part. A recent study found that drumming is a learned behavior, both functionally and neurologically similar to that of songs/calls.
Since songs of birds are species specific, it would seem to follow that drumming would work similarly, that is, you would be able to identify different species of woodpeckers by their pattern of drumming. But a study in France demonstrated that the level of identification accuracy was only 70%. In another study in California, there was also no clear answer. Accurate identification varied with species and habitat. For example, accurate identification of the Northern Flicker varied from 33% in a coniferous forest to 53% is oak woodlands. You can listen to some drumming here. But if one includes all sounds, a study in Spain indicates a 94% accurate identification.
There is no agreement as to whether drumming effectively communicates species-specific information to other species. Two explanations are possible. Perhaps drums are only species-specific or it may be that drums may not be distinctive because other signals are used for species identification – plumages, behavior and calls, for example.
There are several cases of documented or suspected hybridization among woodpecker species such as Red-bellied and Golden-fronted Woodpeckers in North America, two species of Flame-backed Woodpeckers in Sri Lanka, three species of sapsuckers in British Columbia, Great Spotted and Syrian Woodpeckers in Europe, and others.
Woodpeckers evolved about six million years ago. As any group of organisms evolve, changes occur over time, some species going extinct and others arising. (Perhaps as many as 150,000 to 1.5 million birds have existed since they first arose, all but today’s ten thousand gone.) In the process, birds (and other organisms) develop species-isolating features – different physical features, behavior, or calls – to guard against hybridization. But in some species the isolating factors aren’t strong enough.
Given that researchers have not been able to definitively identify drumming calls with substantial accuracy, it could be that drumming is not a major isolating mechanism among woodpeckers. Although we can analyze drumming, calls, and songs with sophisticated sound equipment and see the difference in frequency, duration, and loudness, those qualities do not necessarily reflect what the receiving bird actually hears. For example, humans interpret sounds in chunks that are around 1/20 of a second, while birds can distinguish sounds that are almost 1/200 of a second. So when humans hear just one note, a bird may perceive up to ten distinct notes. Looking for a research project? Here you are.