nature
Peck perfect

Lt-Gen Baljit Singh (retd) tries to answer why woodpeckers don’t get brain damage while seeking food or making cavities on hard surface

THERE is a tall dontha tree (anogeissus latifolia) in our compound. Its cylindrical bole, fat, pale grey, smooth textured and bereft of branches up to 10m, rises straight as a mast. Its unique bole is a favourite feeding space of the white-naped woodpeckers, usually during May and June, the period of peak growth of their juveniles before they become independent. I watched two groups on several afternoons on this tree always between 3 p.m. and 4 p.m. If one group was on the tree, the other either did not show up at all or arrived once the bole was vacated.

They delighted me with their dexterity in hitching up the bole in jerky short spurts, maintaining a straight row with about two body lengths from the one above and pausing at intervals to hammer at the bole with persistence and precision to take out the food.

There were times when one or more of the group would sidestep to scout for food, but no sooner than it was time to resume the hitching spurts up the bole, they would all fall back in line as a group first. Occasionally, they would also spiral around and up the bole, but even so maintaining the spacing (in a skewed row now), while searching out the bole along its entire girth.

The most amusing part was when the group would effortlessly slip into reverse gear, taking the slide again in short spurts, but so synchronously that there was not the least noticeable change in the mutual separation gap nor a flaw in the straight row. And all this accomplished while they looked skyward without so much as stealing even a glance over their shoulders.

While I marvelled at the speed and precision of hammering at the hard wood of the bole, I wondered how the bird avoided injury from the force of such prolonged lifelong impact. The bird books in my collection provided no answer. Fellow bird enthusiasts offered conjectures, but none were satisfying. At last through the "Know How" column in the Telegraph (Kolkata), the decade-old inquiry was laid to rest. I reproduce the text.

"Why don’t woodpeckers get brain damage?

The ‘Know How’ team explains:

"Filmed analysis of a woodpecker shows that the force of deceleration when its beak strikes the trunk is up to 1,200 times the force of gravity. It has to close its eyes just before impact to stop its eyeballs flying out.

The woodpecker keeps its head absolutely straight while striking. This avoids rotational forces, which can cause concussion. Also, its head is constructed such that shock waves are transmitted less readily. It has a narrow space between the skull and the brain, with very little fluid.

The brain is packed tightly by dense yet spongy bone, which buffers the force. Additionally, some of the muscles in the woodpeckers head contract, which helps to absorb and distribute the shock. Structures from the base of the tongue extend round the brain and may also absorb shocks."

Can we safely assume that all species of birds that either seek out food or make nesting cavities by impacting their beaks on hard surfaces have the structure of their beak, skull and cervical region similar to woodpeckers?

I also have one field observation on the yellow-crowned woodpecker, which might be of interest to some readers. I used to see this woodpecker often in March and April when their favourite tree, the Indian laburnum (cassia fistula) is almost totally leafless, but loaded with ripe seedpods, the cherished seasonal delicacy of this woodpecker.

The pods are cylindrical about 40 cm long and two cm in diameter, with a dark brown sheath, the thickness of a postcard. In March and April, the sheath (skin) is crisp and dry, but the light brown pulp inside is moist, sticky and densely packed concealing 40 to 100 seeds.

The pods hang from branches and sway with the breeze like a pendulum. These tiny woodpeckers are crazy about the pulp inside the pods, but getting through to the delicacy is no easy task.

One might think that puncturing the thin sheath of the pod would be child’s play for the woodpeckers. Far from so. The moment the woodpecker attaches itself to the pod combined with the velocity of hammering sets the pod and the woodpecker swaying and in the process there is possibly some loss in the impact of hammering. But the bird perseveres, getting so engrossed, that with care one can get to watch them from close quarters.

Finally, the bird does get access to the pulp, but only at one cm cross-section of the pod and it still has at least another 30 cm to explore. So you can watch them for days and at the end collect a souvenir as well.

The pod would now have shed from the branch in a natural way and it would have a number of rectangular and circular holes, at times circular only and almost in a row, resembling the flute. I do not know if these birds eat the seeds too.

But they certainly are the most efficient dispensers of seeds since in 11 years we have five more Indian laburnums, within 20m of the original two. As the shape and size of the pod resembles the tail of a monkey, the adivasis of the Chottanangpur have named the Indian laburnum ‘Bundar Loria".

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