A natural pest control agent?

A black-rumped flameback on what is left of a cut branch of a neem tree at the Selaiyur lake, on October 6, 2021. Photo: Prince Frederick  

With its reputation as “woodworker” preceding it, a woodpecker may carry blood on its head that it never spilt. The uninformed and superficial observer may take every tap of its beak on wood for hole-making, territory-expanding self-aggrandisement. Having wrapped ts head neatly around the 80-20 pareto principle, the woodpecker makes its job easier by seeking out dead or partly weakened trees to drill its nest in, and invariably leaves the hole behind as a hand-me-down for other bird species to occupy and raise their young. More about this “altruism” later.

With almost every other tap, the woodpecker is prospecting for insects that occupy the furrows and crevices of the bark. It can also look for insects in damaged sections of trees, and may in the process even get rid of certain tree-boring insects what larvae can damage trees unseen. ‘Borer’ signifies one stage in the development cycle of these insects, when as larvae, they do the damage.

The black-rumped flameback occurs commonly in Chennai and surrounding areas, even in urban patches marked by a thick stand of trees, and a familiar snapshot is that of the bird at its post, diligently pecking away at a coconut tree. Scour eBird for black-rumped flameback sightings in Chennai, and the effort would dredge up addresses that connote the hubbub of city life. However, a black-rumped flameback sighting in urban spaces is hardly effortless, and there are obvious advantages in trying to turn this situation around. We will get to the how of it in a while.

“There are a lot of studies in different places in the past that have shown that woodpeckers can control insect infestation of trees to some degree in temperate regions. But now, despite greater diversity of tree life, tropical regions are commonly hit by pest infestations on account of monoculture,” remarks ornithologist V Santharam, who has himself conducted an elaborate study of the eight woodpecker species found in the western ghats.

While conceding that woodpeckers make short work of insects they find on tree surfaces, including exposed parts of cut branches, he is not certain if they would go to the trouble of drilling to get at borer-insects, actually their larvae.

“Talking of insects that bore into wood, you need a woodpecker species that feeds on insects by making a hole. Woodpeckers have long, sticky tongues that they can insert into those galleries and grab insects. The larvae of borer-insects make holes as they go in, and woodpeckers may slightly enlarge the hole made by the borers and stick the tongue in and get them. When I studied the eight woodpecker species in the Western ghats at Peechi wildlife sanctuary, I found that many of the woodpeckers were reluctant to dig into the wood. To drill into the tree, they have to expend lot more energy pecking at the tree. Most of the time, they were feeding on insects found on the surface. They can get at the termites by digging a little bit and slightly disturbing the gallery. The ants are similarly taken. When food is available in plenty on the surface, why would they want to drill holes to reach for borers? Of course, if the borer-larvae are just under the barks, the woodpeckers will surely take them. Woodpeckers sometimes take insects that can harm trees and are therefore known as wood doctors.”

The shape of the beak is a factor deciding how far a woodpecker would go for a meal.

“The beak structure would to some extent tell you whether the bird is capable of making that hole. The black-rumped flameback has a bill that is slightly curved, which can be a limiting factor. Out of the eight species I studied, two — the greater golden-backed woodpecker and the black woodpecker — were spending more time getting things done inside the tree and not just on the surface.”

While fungi infestation is not good news for a tree, it certainly is for a woodpecker.

“Many of the woodpeckers use trees that are infested with fungi so that boring a hole becomes much easier. Once woodpeckers make a hole in a dead tree — as decay happens slowly, the tree would be standing for 10 to 15 years — it is available for other hole-nesting birds like mynahs and parakeets and barbets. In my study, I noticed that 40 p.c. of the birds found in that forest were hole nesters and they depended on cavities created by woodpeckers for nesting.”

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Printable version | Nov 28, 2021 8:58:39 AM | https://www.thehindu.com/sci-tech/energy-and-environment/a-natural-pest-control-agent/article36915008.ece

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