Woodpeckers

Lesser goldenback woodpecker,
showing tongue. Photo: Ihtisham Kabir

Twenty five miles per hour. That's how fast a woodpecker's beak travels when it hammers the tree. This impact, so close to the head, would render most creatures senseless - or at least give them a massive headache. But woodpecker brains are cushioned to absorb the shock. Hence they can keep hammering – some of them go as fast as twenty times a second – without feeling anything.
There are over 180 species of woodpeckers in the world. According to the Encyclopedia of Flora and Fauna of Bangladesh there are 16 species in Bangladesh. Of these, six are common and the rest are considered rare or “vagrant.” Our most common woodpecker is the lesser goldenback woodpecker (dinopium benghalense) which has adapted well to humans and is often found in trees close to cities and farms.
Everything about a woodpecker seems fine-tuned to a life spent hitting trees with its beak. Take, for example, the two halves of its beak (called mandibles.) With the high-speed impact, they would have flown open, but woodpecker mandibles have a special locking mechanism that keeps them together.
Then there are the feet. Woodpeckers have zygodactyl feet – that is, two of their toes point forward and two toes point backward. This helps them stand at odd angles on tree trunks and climb them in a spiral pattern using short jumps. Their stiff tail supports them in this activity.
Hammering trees serves many functions for woodpeckers. They make nest holes by drilling with the beak. Some species of woodpeckers communicate by making drum-like rattling sounds with their beak. In particular, during mating season, they drum on hollow objects to attract potential mates.
But perhaps the most important purpose of pecking on trees is to find cavities containing their food, which consists of bugs, larva, insect eggs, caterpillars, etc. Tree beetles and other insects sometimes burrow elaborate tunnels inside trees. From the sound of impact, woodpeckers can tell if the tree is hollow; they sometimes cock their ear to hear the movement of insects inside.
Once they detect prey inside the cavity they drill a hole with their beak. But how do they extract this food? That's when their tongue comes useful. Woodpeckers have long and narrow tongues, sometimes three or four times the length of their beak.  The tongues are wrapped around the inside of their skull and covered in tiny barbs or sticky mucous. When they insert the tongue into the just-drilled cavity, their prey gets stuck on it.
Largest woodpecker in the world is the great slaty woodpecker of southeast Asia, measuring 20 inches. Piculet woodpeckers, measuring four inches, are the smallest.
Although the lesser goldenback can be observed in trees in many parts of the city, I have found that the best place to see them is the Mirpur Botanical Garden. There, you can observe its typical flight: several energetic flaps of the wings followed by gliding with wings tucked in. With luck, you might also see it catch a prey from a tree cavity.

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