Bats gorge on Debdaru fruit and ‘grin in their sleep’!
It is humbling to note that the bat is the only mammal that can fly. Although a few squirrels and colugos can glide, no mammal other than the bat is able to fly proficiently
A bat with big, bulging eyes stared at us from a swaying branch of Debdaru tree along the street we were walking at sundown. We took a break from our evening walk to investigate why suddenly the noble Debdaru trees were raining seeds on a motley group of passersby.
The acrobatic bat hanging upside down quickly resumed its intense chewing on the green fruits of Debdaru and let the seeds stream down on us. The sharp-eyed bat must have recognised us as his mammalian relatives and decided to shower us with some fresh seeds.
We were glad to see Debdaru seeds all along our track. Seed dispersal is a great service of the bats to earth, especially to the tropical rain-forests with more than 90% of plants and animals of the world. Bat is the most important vector of regeneration of the tropical forests.
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It is humbling to note that the bat is the only mammal that can fly. Although a few squirrels and colugos can glide, no mammal other than the bat is able to fly proficiently. Using this unique gift of flight, the bats managed to colonise all the six habitable continents of the world.
There are over 1400 species of bats in the world even though Bangladesh has only about 35. The fellow hanging from the Debdaru tree, known as the Indian Flying Fox, was one of the largest bats of the world. It weighed no less than 1.5 kg; a goliath of our nighttime sky.
We wondered how the bat could obtain enough energy by gorging on a thin layer of the green flesh of Debdaru fruits. These roadside Debdaru trees may be their main source of food in the city now as the season of Banyan fruits, the bats' most favourite food, has come to an end.
One of our beloved English authors of the twentieth century, D.H. Lawrence, was captivated by the odd manners and strange lifestyle of the bats. In one of the poems on bat he wrote:
'Creatures that hang themselves up like an old rag, to sleep;
… And grinning in their sleep.'
In a colony of Indian Flying Fox at the Ramna Garden we saw over a hundred bats hanging from the tree-branches like the 'old rags'. But being ceaselessly engaged in screaming contests with one another, most of them were not going 'to sleep.'
The few bats not screaming at Ramna were the diligent ones meticulously cleaning their precious wings with the only mop they possessed - the big orange tongue. With a huge wingspan of five feet the bats' chores did involve vacuuming a lot of 'old rags' indeed.
The few bats quietly hanging from the trees while tightly wrapped in their wings were, probably, asleep. We could not tell if they were also 'grinning in their sleep'. It took no less than an imaginative twentieth century poet to perceive a spectacle as fleeting as a bat's grin!
As soon as the sun hailed from the clouds the bats of Ramna came out of their rags and started fanning them with their wings. The males dutifully fanned more vigorously to spread the aroma of their male-hood to the nearby females. August is the time to signal that the males are getting ready. In September they will be most fecund.
Like most mammals the bats do not form male-female pairs. Both sexes of the Indian Flying Fox believe in free sex and neither sex maintains a family or a harem. A female carries her fetus for five months and suckles her baby for five months; and has only two unfettered months a year.
Baby-bats are born in spring. They learn to fly in three months but cling to their moms for two more months. Babies become adults in two years and remain agile and fertile for 30 years or more. In a scale of comparative body size, bats are the longest living mammals of the world.
The secret of the remarkably long life of the bat may lie in two of its genetic attributes. One - a unique immune system allowing the bat to host a whole lot of viruses without falling ill. Two - bat's telomere shortens at a slow pace. Scientists are racing to learn more of bat genetics and use the knowledge to extend human lives.
Outside the scientific world, however, the bats have always been more detested or feared than adored or idolised. Our ancestors imagined Satan as the spirit of dark recess just like the bat. Artists have always drawn the angels with bird-wings; but the Satan with bat-wings.
Leonardo Da Vinci was a huge exception. He was charmed by the bats; and designed the wings of his flying machine after those of the bat. Some 500 years back, he drew 500 sketches of flying machines and wrote '.. flying machine must imitate the bat..'. Was Leonardo right!
A bat's wings and its modes of flying are far more complicated than that of the birds. The bird-wings are paired and can only move in unison; when the bat moves each wing independently and executes violent turns well beyond the capacity of any bird. Do humans need a bat-like flying machine?
Humans have been using flying machines for over a hundred years now. None of those machines imitated the bat. That is because humans are simpler creatures and their flights need not be as convoluted as a bat's flight. Human existence has not been as challenging as the bats'.
