What the bats see and the owls hear

Santanu Chakraborty | Updated on April 10, 2020 Published on April 10, 2020

On watch: Owls can hear about the same range of frequencies as humans but are far more sensitive to the slightest rustle made by their prey   -  GN RAO

The lockdown is a good time to remember the remarkable capabilities of organisms we’ve learned to ignore

A new pandemic virus is upon us. Having sent the whole world into varying degrees of lockdown, it continues to spread. With the likelihood of long quarantines looming around the world, many are finding out how difficult it is to stay indoors pretty much all the time. Some miss the socialising in a city, others the solitude of a walk in nature and still others miss the freedom to travel at the drop of a hat. That these privileges vanished overnight is causing such difficulty that there are warnings about mental health doing the rounds. We could all do with some uplifting news.

However, one first needs to be wary of the fake news about animals reclaiming the earth that is taking over social media. A virus that gets us to lie more — now that is trouble.

Amidst all this doom and gloom, a group of scientists has decided to turn the crisis into an opportunity by calling for citizens to record and observe wildlife in their neighbourhood. This will allow systematic studies, with multiple observations and verifications, to deliver some hard facts on the effect the sudden disappearance of humans is having on the outdoors. One such exercise is the Lockdown Birding Challenge (https://birdcount.in/lockdown-birding-challenge/), which calls for citizens and scientists to record sightings of birds outside their window for just 15 minutes in the morning and in the evening. The sightings are then uploaded to a central server so that hundreds of contributions can be assembled and rigorously analysed. It is only through such continued and slow processes that we can get a handle on the facts. Ecologists who spend a lot of time observing nature and its associated organisms, or their lack thereof, can better gauge if something unusual is happening.

So I decided to speak to Abhisheka Gopal, a Bengaluru-based ecologist, about her preliminary findings from the bird count challenge as well as her observations on changes in animal life in her neighbourhood on the outskirts of the city.

These are her sightings:

First-time sighting of Indian grey hornbill and tawny-bellied babbler in the garden.

A pair of white-browed bulbul often seen. They may be nesting.

A pair of grey francolin regularly visits an empty site next door.

Indian grey mongoose with two pups seen twice in the empty site, spending time without the fear of human disturbance.

Bird calls from far, especially of the peafowl, are audible due to absence of vehicular noise.

Based on her observations, she tends to think that many species of birds are travelling further into the cities and are less afraid. But she is apprehensive of what will happen to the chicks hatched in an urban area during the quiet of the lockdown after humans take back these spaces. Imagine living in a clean, quiet and unpolluted space all your young life, and then being shoved into noise.

In the unwavering focus on our selves, we forget the other organisms that inhabit the earth. Human aggression disrupts the intricate balances that enable all life. To appreciate the other life forms on earth, it might help to remember the remarkable capabilities of those that we have become accustomed to ignoring.

Some species of bats, for instance, can ‘see’ in the dark but by using sound. They produce high-frequency sounds beyond the limits of human hearing. When these sounds strike an object, say a flying insect, a very tiny fraction of it is reflected back to be detected by the bat’s ears and processed by its brain to determine the exact location of the insect. This process is extremely complicated and akin to the sonar and radar systems used for navigation by submarines and aircraft. Sophisticated forms of locating by sound are also found in some whales and dolphins. Scientists continue to study these systems and are impressed by how these animals can function accurately even in the midst of noise produced by humans.

If bats have evolved to work with sounds outside the human range of hearing, owls can hear about the same range of frequencies as humans but are far more sensitive to the slightest rustle made by their prey. Their adaptations are nothing short of astounding. A barn owl’s ears are just next to its front-facing eyes. But its face is set in a slightly inward curving hollow. The shape of this disc and some of the feathers around it can be altered by the musculature underneath to help focus the incoming sounds into the ears.

Couple this with an acute ability to sense and ‘count’ small increments of time and the owl has a way of knowing precisely where the sound came from. If the sound reached the left ear a tiny bit (say 0.2 milliseconds) before it was felt in the right ear, then it’s coming roughly from the left.

Owls have one ear set slightly higher than the other. If the lower ear detects the sound first then its source must be below the owl. Some owls have combined this ability with another one: Near-silent flight, so as to not alert their prey or predators or mess up their own ability to hear. Imagine how they would feel in the cacophony of traffic noises that can drive even humans up the wall. For them it is a matter of life and death.

So the next time you go out into the city or near the woods, tone it down a bit and make room — in your concept of the universe — for creatures other than your own.

Santanu Chakraborty   -  BUSINESS LINE


Santanu Chakraborty is a Bengaluru-based engineer, scientist and photographer.

Published on April 10, 2020

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