(IN): Canopy Crawlers

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Canopy Crawlers by Abjijit das

 

*S*nakes are incredibly successful, unique and remarkable animals, deserving

well our respect and admiration. Their grace, agility, variability and

adaptability are unmatched in nature. Utilizing the advantages of a

cylindrical, legless body, they adapt themselves in best possible ways to

variety of terrestrial, aquatic and arboreal niches of earth.

 

Among different groups of snakes, the 'arboreal snakes' reached the zenith

of reptilian evolution and modified themselves in a unique way to lead a

life above ground, mostly on vegetation, thus to become the only arboreal

vertebrate without hands, wings or legs. Of them a few are swift movers,

some are expert climbers, some canopy gliders and some remain perfectly

camouflaged with their surrounding green vegetation.

 

Of the 275 species of snakes so far known from India, 17 per cent species

are regarded as 'largely arboreal' in their habit and spend much of their

lifetime crawling among forest canopy. This arboreal guild of serpents shows

specific morphological adaptations, which distinguishes them as a group.

Their light and pneumatic body, better belly grip, prehensile tail and

camouflaged colourations are just perfect for an arboreal mode of life. With

one or all of these adaptations, the tree creepers of Northeast India are

represented by vine snakes, bronze back tree snakes, cat snakes, flying

snakes, tree racers and green pit vipers.

 

Vine snakes are the most unique among all tree snakes as they have a long

pointed snout and unlike any other snakes their pupil is horizontally

placed. Vine snakes are generally green coloured but may also be

yellowish.These day-active snakes remain extremely camouflaged among

top fronds of

bushes, scrub vegetation or among elephant grasses where they either bask in

the morning sun or wait in ambush for their preys like lizards, small birds

and tree frogs.

 

All the vine snakes are ovoviviparous which means their eggs hatch within

mother's body and thus give live births to the young. A bite from this

nonvenomous snake may produce nothing more than mild pain and slight local

swelling to humans. However, in many areas, it is foolishly believed that

vine snakes will dart at a person's eye and peck them out!

 

Next remarkable group of tree snakes are the bronze back tree snakes

represented in the Northeast by five species. Locally known as karsola saap,

these slender and extremely agile snakes attain a length of 1-1.5 metre.

These diurnally active snakes, though largely arboreal, often come down to

ground where they move rapidly with fore body erect but when threatened,

they always try to climb trees or bushes with amazing speed. Their body

colouration is decidedly protective and when the snake is still, it bears

remarkable similarity to a small dry tree branches, thus avoiding predator

attention. They also have the ability to spring and can be seen leaping

between treetops. These snakes feed on lizards and frogs and are totally

harmless to humans. Bronze backs lay eggs inside bamboos, tree hole or old

bird nest.

 

However, the most elusive among all tree serpents are the cat snakes. They

are called cat snake (Assamese — *mekuri saap*) because of their eyes which

resemble those of a cat with a vertically elliptical pupil. All the eight

cat snake species of the Northeast appear to have been restricted to the

Eastern Himalayas, Assam plains and Myanmar border and are rare at regional

and global scale. Most of these nocturnal arboreal reptiles are adapted to

forested habitats of hills and foothills inhabiting bushes, shrubs to high

trees. During day time, they rest inside tree holes and rocky crevices by

coiling themselves into a ball rather than lie extended as do other tree

snakes like vine or bronze back snakes. None of these snakes are known to

exceed a length of two metres. Their food as one would expect from their

arboreal habits consists mainly of birds, their eggs, bats, and arboreal

garden lizards. Cat snakes lay 3-10 eggs at a time. They are back-fanged

snakes and have mild venom for paralyzing their prey. But for humans they

are harmless and often inoffensive creatures. When disturbed, they open

mouth widely, coil tightly and put on an S-shaped defensive show, rearing

back and vibrating the tail, a behaviour similar to famous American rattle

snake.

 

Brightly coloured and beautifully ornate, flying snake *Chrysopelia ornata

*is the most ornamental and colourful among all canopy crawlers with yellow

and black banded head; the back is black, beautifully marked with yellow and

white cross bands and speckles of red rosettes. This is one of the most

popular snakes and almost a common item for snake charmers who call it *

kalnagin* and tout this harmless snake as deadly venomous. This medium sized

slender snake is not known to exceed a length of 1.75 metre. However, the

most important characteristics of this snake is its remarkable gliding

ability. This snake generally glide from a height of 15-20 feet above

ground, straightening itself out and hollowing the ventral surface as it

moves through air producing a mechanical effect for impending the action of

gravity and fall at an angle to the ground, thus reducing the speed of

descent. It's a breathtaking experience to see such magnificent gliding

ability of flying snakes between some of the last remaining evergreen forest

canopies of Northeast India.

 

Flying snakes are active by day when they search for their favourite food —

lizards and small birds. They are known to lay 6-20 eggs in tree holes

during May and June, which incubate in 60-80 days.

 

Most graceful however, among all tree creepers are the pit vipers. There

are nine species of pit vipers known from Northeast India among which six

are 'largely arboreal' in their habits. All the pit vipers are quite a

distinct group of snakes with a broad flat and triangular head, a thick,

plummy and short body, short but prehensile tail. None of this species is

known to exceed a length of 1.5 metre. They are called pit vipers because

all of them have a pair of heat sensory pits located between their eye and

nostril, which help them to locate their warm-blooded prey. This remarkable

adaptation is believed to be the most recent in reptilian evolution.

 

All the green pit vipers are largely arboreal and they actively hunt their

preys like small mammals, birds, lizards and sometime frogs during night.

Usually sluggish during the day they often recline on branches four to eight

metres above ground, on bamboo clumps or on vegetation near hill streams,

their colouration merging with the surroundings. When provoked to strike,

they anchor themselves firmly by the tail and hind body to a branch and with

rest of the body in a broad 'S' shape and strikes with lightning speed as

far as it can straighten itself. They are ovoviviparous and known to produce

3-12 live youngs at a time. Pit vipers contain venomous properties and their

venom delivery system is considered as one of the most advanced types in

animal kingdom. But their venom is not as potent as terrestrial venomous

serpents like cobra and krait. However, under extreme provocation a bite

from pit viper can produce great deal of local effect in humans like

swelling of bitten part, tissue necrosis and intense pain which may last for

a week or two. Instead of traditional treatments like cutting, tying or

sucking the bitten part, proper medical management of a pit viper bite can

surely save a patient.

 

Unfortunately, these magnificent evolutionary gifts of nature are

increasingly facing extinction crisis as their forest habitats are being

destroyed and isolated. As the humid tropical evergreen forests of Northeast

India, which are repository of biodiversity together with many rare and

unique reptiles, are under severe onslaught of destruction from excessive

jhum cultivation and heavy timber extraction which can spell disaster for

canopy dependent reptiles. Similarly, unsustainable removal of bamboo

forests can affect many specialist bamboo dependent species of pit vipers.

 

With the increase in development activities many of the forested habitats

are fragmented from road construction. As a result many of the snakes are

killed by speeding vehicles during their movements between habitats.

 

In our yearlong study on herpetofauna of Kaziranga National Park we

recorded such huge loss particularly during rainy seasons, and curiously

enough we found that out of the total number of snakes killed on road, tree

snakes dominate the list and individuals of the species eastern cat snake

were killed more than any other reptile species.

 

Actual reason of this vulnerability of arboreal snakes from vehicular

traffic remains to be answered, but we have observed that compared to other

terrestrial snakes, their movement on a paved road is relatively slow and it

may be a reason for their vulnerability from vehicular traffic. However, it

is true that such kind of persistent loss at a particular region may lead a

locally abundant species to extinction.

 

Being a distinct ecological guild adapted to different arboreal strata like

lower storey, mid storey and top canopy of a forest ecosystem, tree snakes

can be of immense conservation value as their abundance and diversity will

reflect the whole ecosystem structure, function and condition. Also all of

them being predators, their richness in a habitat will indicate a healthy

and diverse assemblage of prey base. A serious effort to know the little

known life history strategies of these canopy crawlers can go a long way in

understanding and conserving the complex yet highly threatened forest

ecosystems of Northeast India.

 

*Abhijit Das*

 

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