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Part II: How Mother Nature’s air-to-air hunters keep pest numbers down

The swifts, swallows and nightjars go in for insects on the wing, have niche hunting blocks, different attack hours, and, sensibly, avoid the stingers — bees and wasps

Written by Ranjit Lal |
Updated: September 12, 2021 9:33:16 am
sunday eye, ranjit lalA young wire-tailed swallow stretches its wings. (Source: Ranjit Lal)

Raptors take down their kills one at a time. But the fastback fighters, part of Mother Nature’s Air Force (MNAF) we’ll meet now, go wholesale to keep pest numbers down. We’ll meet three specialists: the swifts, swallows and secretive mottled nightjars. All three go in for insects on the wing, have niche hunting blocks and different attack hours. Sensibly, all three avoid the stingers: bees and wasps. They have narrow swept-back wings, and deeply-forked tails, designed for high speeds and astonishing maneuverability. They have especially wide gapes and unlike the raptors, their kill weapon is their bill — not their feet, which, in fact, are weak and flimsy.

The eyes of swallows are especially designed to see in “slow motion”, like a phased-down strobe. They have two areas of sharp focus in each retina (called fovea): one is used for sighting prey (long distance) and the other for capture (short distance). Nightjars have a reflective layer at the back of the eye to assist night vision and long, rectal bristles for eyelashes which guide targets to the gape and protect the eye when the birds zoom into swarms of insects.

Of the three, the swifts are the high-flying speedsters. With their narrow, swept-back wings they scissor the skies at an altitude of 50-100 m, but can go up to 1,000 m, if that’s where the swarms of insects have been taken by air currents. They can clock 250 kmph (one incredible report noted 400 kmph — peregrine speed!) flying over 800 km a day, perching briefly or roosting for the night on rocky ledges, cliff faces or ancient monuments. Their heavy and stiff wing bones give them the power for endurance and speed and air currents (vortices) generated by their narrow wing tips that enable them to obtain greater lift and take down thousands of smaller insects, midges, mosquitoes, and tiny spiderlings borne up by air-currents.

Insects are scooped into the wide gape and lodged in a pouch at the back of the throat, forming a bolus, comprising around 1,000 insects before being swallowed or regurgitated to progeny. Eating, sleeping, and mating are all done on the wing. Swifts are usually brown above and white below. Those living in temperate areas are migratory, heading south in winter as insects die out.

The most famous and popular of the trio are the swallows. Though shaped like swifts, they’re unrelated (convergent evolution!). But their plumage is usually a metallic dark blue, with white and red. They hunt larger insects — flies and mosquitoes — at lower altitudes. Many patrol rivers, lakes and other waterbodies, flying low over the water, snapping up the insects hovering over it and dipping their beaks in for a quick drink: I’ve watched them beat up and down the moats at Delhi’s National Zoological Park and over the Yamuna (one tip for photographers: watch how they fly downwind and upwind while on beat patrol over a waterbody: they’re much slower upwind and, hence, easier to track!) Like the swifts, they are diurnal.

And of the 90-odd species, the barn swallow, found ubiquitously around the world, is the most popular. Their wings are more flexible and lighter than that of the swift. Swallows are famous for lining up on wires especially while gathering for their great migratory flights away from the evil winter’s chill in the northern hemisphere. Those in Europe fly down to Africa’s welcoming warmth, some may clock 9,000 km on their trips between North, South and Central America. It’s believed, there are around 190 million swallows worldwide, eating 65 billion insects daily: economists and politicians can calculate how that monetises. If swallows feel humans threaten their broods, they will dive-bomb us!

The most secretive of the trio are the nightjars, aka nighthawks: these nocturnal and crepuscular hunters lie furtively low during the day, usually dressed in the exact colours and patterns of the branch or ground they choose to roost upon. Mottled and dappled, they are invisible during the day. Come dusk and dawn, and they’ll be up and hunting — moths, mosquitoes and other insects. Larger than swallows, they have huge and wide eyes on either side of their heads for binocular vision. From high over the canopy, they’ll dive-bomb their victims on softly-feathered silent wings, or patrol areas where pools of light attract clans of frenziedly dancing moths and beetles. They net their victims by flying mouth-open!

Unfortunately, they are fond of roosting on roads and get dazzled (and frequently killed) by traffic. They twist and turn in the headlights’ beam, softly uttering “chuck-chuck” calls as they hawk the dancing doomed insects. Needless to add, they love full-moon nights for good hunting! Next week, we meet the “perch-to-air” and “air-to-water” missiles of the MNAF!

(Ranjit Lal is an author, environmentalist and bird watcher)

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