Knock, knock, knocking

Two of my early memories merged together very strangely. One is that of the boy who could not keep up with the Pied Piper of Hamelin and spent his life trying to find the place where the piper was leading his friends to. The other is Bob Dylan’s song from which the title of this post is taken. When I hear a woodpecker knocking madly at a tree, they trigger this little chunk of memory in me. As I sat after lunch under a tree in the jungle in Bhitarkanika, I heard the drumming sound of a woodpecker, and came out to look. I saw this wonderful flame back woodpecker searching for its version of paradise.

If I were to hit my face rapidly and at high-speed against a tree, I would knock myself out in a few tries. The reasons that a woodpecker survives are visible in the photo. They have to do with modifications to the spine and the way the head is attached to it.

The most visible adaptation is the shape of the head. The elongated wedge shape of the head is due to two factors: first the bones at the front of the skull have thickened, and the muscles at the front, which anchor the beak, are immense and serve as shock absorbers. It seems that there are also adaptations in the way the brain is attached to the skull which prevents it from slowly being battered.

Another easily observed adaptation is the wide shoulders. This is due to the enlargement of the first set of ribs. The expanded ribs anchor very strong muscles which serve to hold the neck steady. The woodpecker strikes only at right angles to the surface, so that the beak and neck muscles can damp the recoil. A sideways strike would twist its neck.

A third adaptation is visible in the photo: the stiff black tail feathers. These balance the woodpecker in its vertical stance on a tree as it drums away. Apparently the last few spinal bones are fused to stabilize the woodpecker. The toes are also adapted to hold on to trunks of trees.

All of these features are generic to woodpeckers. The shape of the head, the wide shoulders, the stiff black tail feathers, just a glimpse of these is enough to tell you that the bird you are looking at is a woodpecker.

Woodpeckers may have begun to evolve about 40 million years ago, when the shifting of continents began to create today’s weather. The resulting spread of angiosperms and the conversion of sub-tropical forests to deciduous forests created the conditions which we see today. This opened up the ecological niches which the woodpeckers fill today. So many changes are required to adapt to a lifestyle based on digging insects out of the bark of a tree!

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