Many birds can identify each other by the songs they make, from penguin chicks picking out their parents in a crowd of thousands to albatrosses finding their long-term mate each year. But woodpeckers aren’t exactly the most vocal of birds. New research suggests that rather than calling to each other, woodpeckers can tell exactly who someone is by the rhythm and pattern of their drumming.
It seems obvious to us that the birds are drumming against trees to make noise and using the natural resonance of the wood to enhance it, but this wasn’t always the case. Even well into the 1940s, some people continued to argue that the birds were physically producing the sounds themselves. The argument was finally put to rest in 1943 when one bird watcher put a microphone inside a tree to record the drumming.
We know that woodpeckers use the drumming for communication, as each species has its own unique drum roll that can be used to identify them. The drum rolls vary in the pattern of beats, the length between taps, and the cadence.
In effect, the drum roll is used by males for the same reason that songbirds tweet their tunes, in order to stake their claim to a certain patch of woodland and assert their dominance. They have even been known to select specific trees that have a higher resonance, such as hollow ones, or conduct their drum rolls on man-made surfaces such as metal patches on telegraph poles or public address tannoys. In light of this, males tend to drum more frequently than females.
However, the birds might be able to use the rhythm and pattern of the drumming not only to distinguish between sexes but also individuals. New research, published in the journal Plos One, compared the rapid pecking of 41 great spotted woodpeckers, specifically looking at the length of time between pecks and the number of strokes during the drum rolls.
It turns out that in around 86 percent of the cases, the drum roll can be assigned to certain individuals. They found that in general, the males had shorter intervals between strokes, meaning they were drumming faster. This suggests the tapping may be more than simply a territorial display, it could also be used to identify each other.
But the birds might not only be using the drumming to tell each other apart, they could also be using the tap-tapping to assess the quality of a potential mate. It takes well-developed, strong neck and back muscles to drum rapidly against the trees. In theory at least, females might be able to use this as a proxy for which males are the fittest.