Russell's Viper

Russel's viper (Daboia russelli) is a large species of viper found throughout the Indian subcontinent and other parts of south-east Asia.  Most of the snakebites (about 50%) in the Indian subcontinent are caused by the Russell's viper.

Physical Features
The russell's viper is a large and bulky viper, normally growing about 1 to 1.2 meters long.  However, specimens over 1.5 m have been recorded.  The color of their dorsal side is generally brown of varying shades, tan or deep yellow.  Their are a series of dark ovals running along their back which are outlined successively by black and white.  Another series of similar ovals runs down each flank alternating with those on the back.  They have a triangular head with a blunt snout.  Their head is very distinct from the body and they have very short tails.  Their belly is white, yellowish or sometimes pinkish.  The coat of the russell's viper very closely resembles that of the rough scaled boa, a harmless snake.

Distribution and Habitat
The russell's viper is widespread in the Indian subcontinent and is also found in Thailand and the Indo-Australian archipelago.  It is most common in India, Sri Lanka, Pakistan and Myanmar.  It inhabits plains, grasslands and plantations.  However, it has been recorded at heights of 2,100 m in south India and 2,000 m in the Himalayas.  It is common along the west coast of India.  It is abundant in Punjab but quite rare in the Ganga Valley.

Diet
Their diet mainly consists of rodents like mice, rats, squirrels, etc.  However, they will eat anything like lizards, frogs and small birds.  Juveniles are known to be cannibalistic.

Behavior
The russell's viper is largely nocturnal.  Adults are known to be sluggish while juveniles are more excited and alert.  When aggravated, they stand their ground and produce a loud hiss that is distinctly louder than other snakes.  They are slow movers.  However, when they strike, they hurtle themselves with such force that they may even leave the ground.  Adults normally just prefer to just hiss when disturbed while juveniles may be more aggressive and bite.

Reproduction Cycle
Russell's vipers are ovoviviparous.  This is a mode of reproduction where the embryo's develop inside eggs which remains in the mother's stomach till they are ready to hatch.  The embryo's are nourished by the egg yolk. After they hatch, the mother gives birth to them.  A russell's viper generally gives birth to litters of 20 to 40 young.  However they have been known to give birth to litters of 63 individual as well as to a single young.  The gestation period exceeds six months.  Gravid females have been recorded in all months of the year. Females give birth between the months of May and November.  They sexually mature at the age of 2-3 years. 

Venom
A dose of 50-70 mg is lethal to an adult human.  The bite results in immediate pain and swelling in that region.  Post 20 minutes, bleeding occurs in the gums, urine and sometimes sputum.  Necrosis (the premature death of cells due to injuries) is a common symptoms.  Heart rate falls and blood pressure drops.  The victim may die of kidney failure, septicemia or cardiac arrest.  Death from any of these may occur in a period of 1 to 10 days.  Russell's viper used to cause about 300,000 deaths per year in the Indian Subcontinent before the introduction of its antivenin.  This has reduced the deaths by russell's viper considerably. 

Cotton-top Tamarin

The cotton-top tamarin (Saguinus oedipus) is a small species of primate found only in a small part of South America.  It is rated as "Critically Endangered" by the IUCN.  It is a popular exhibit in zoos all around the world.

Physical Features
The cotton-top tamarin is an unmistakable species.  It gets its name from the elegant, long, white flowing fur on its head.  They generally weigh only about 420-450 grams. Their body length can be about 20-25 cm long while their tail can be about 35-40 cm long. Their tail is not prehensile i.e. it has not adapted to hold or manipulate objects. Males and females are generally same in size.  Their face is generally black or gray in color with very fine white hair which is barely visible.  Their back (dorsal side) is covered with brown fur while their front (ventral side) is covered with white or yellowish white fur.  Their tail is also covered in brown fur.  Unlike other monkeys, the cotton-top tamarin's thumbs are not opposable.

Diet

Cotton top tamarin feeding on some dry fruits.

Cotton-top tamarins are omnivorous.  They equally depend on plant material and animal material.  They consume organisms that are smaller than them like small lizards, amphibians and insects. Insects are a main constituents of their diet.  Plant material consists of fruits, flowers, nectar, seeds and plant sap.  They require very nutritious and high energy foods due to their small size and high food intake.  

Distribution and Habitat
The range of cotton-top tamarins are limited to the north-western side of Colombia, between the rivers Atrato,  Cauca and Magdalena.  Even in this region, their habitat is fragmented. They live in both tropical humid forests as well as tropical deciduous forests, primary as well as secondary forests.  They prefer to live in the lower levels of forests but may descend to the ground in search of food or ascend tall trees for protection or food.  They sleep in foliage cover.

Behavior
Cotton-top tamarins are diurnal.  They either live in pairs but more often live in groups. They spend the days foraging and grooming.  They are very social animals and each group may consist 5-15 members.  They follow a matriarchal system i.e. the leader of a group is the eldest female.  Cotton-top tamarins groups follow a "helper" system where males and older siblings take care of the young and newly born for sometime.

Life Cycle and Breeding

Infants along with parent.

In a group of 10-15 individuals normally only one male-female pairs breed.  It is very often for twins to be born.  The breeding season is between the months of April and July.  A female cotton-top tamarin gives birth to a single offspring or twins after a gestation period of 4-5 months.  Males take care and groom the infants more than the female.  Cotton-top tamarins are known to live in captivity for 20 years while in wild, they often live for about 13 to 14 years.

Conservation Status   
The cotton-top tamarin is rated as "Critically Endangered" by the IUCN.  There are approximately 6,000 individuals remaining.  Illegal pet trade and habitat fragmentation is the main cause of population decline.  It is said that between the 1960's and 1970's about 30,000 individuals were exported to the United Sates for bio-medical research.  The population is decreasing.  It was one of the most endangered species of primate in the world between 2008-2011.  It is protected by the law.  The Paramillo National Park is one of the most important stretch of forest for this species and comprises of 1800 square miles.  There are enough number of individuals in captivity for the sustenance of this species.  It is said that their are more captive individuals than wild ones.

Source of pic 2, pic 3 

Bengal Monitor

The Bengal monitor (Varanus bengalensis) is a common, medium sized monitor lizard found in the Indian Subcontinent.  It is rated as " Least Concern" by the IUCN but its population is decreasing due to habitat fragmentation and hunting.

Physical Features

Brightly colored juvenile

The length of a bengal monitor can range from 1 meter to 1.8 meters. Males are larger than females. These monitors can weigh up to 7 kilograms.  Its head is relatively small as compared to the body but its snout is more rounded than the water monitor, which is a main distinction other than the size.  It has a thick and stocky head and short limbs. Adults' dorsal side can be olive, gray, black or brownish in color with sparse black spots. The ventral side is generally yellowish. Juveniles are brightly colored with series of dark bars on the neck and back which are sometimes accompanied by spots.  Bengal monitors have external nostril openings known as nares which they can close on will to prevent the entering of water or any other particulate matter.

Distribution and Habitat
The bengal monitor is the most common monitor in the Indian Subcontinent.   They are also found in Iran, Malysia, Java and Sumatra.  They are absent in the Andaman Islands. They can be found in rainforests, swamps and arid regions.  They are often found in agricultural and cultivated land.  They can be found in burrows, tree hollows and termite mounds.

Diet
They eat insects, small mammals, amphibians and other lizards.  It basically eats anything it can overpower.  They may even scale trees to stalk bats.  Juveniles are almost completely insectivorous.  It is a common sight to see them stealing eggs from nests, be it a bird's or crocodile's.  It senses its prey by both smell and sight.

Habits and Behavior
Bengal monitors are diurnal creatures.  They often dwell in trees or burrows.  Just like snakes, they flick their tongues out to "taste the air".  They can run at high speeds and are very able climbers.  They are also good swimmers.  They are generally very docile creatures.  When alarmed or threatened, it tries lies still to remain unseen or escape notice. When cornered, it may even stand on forelegs and lash its tail repeatedly on the ground. Bites from these monitors are quite painful and once the jaw is embedded into the flesh, it is difficult to remove due to its curved teeth.  They lead a solitary life and have a keen eyesight.

Life Cycle and Breeding

Bengal monitor in Bannerghatta National Park, Karnataka, India.

Bengal monitors are known to survive for 20 years in captivity, though it is generally lesser in the wild.  Males become territorial during the mating season (which they are generally not). Males battles each other for mates by standing up on their hindlegs. Sounds made during the mating season are generally restricted to hissing though bellowing has been recorded.  About 1 to 3 clutches of eggs are laid by the females with each containing about 20-30 eggs.  The female digs a pit to place the eggs and covers it with soil.  She may build a few false pits around it to mislead predators.  The eggs hatch after and incubation period of 6-9 months.

Conservation Status
The bengal monitor is rated as "Least Concern" by the IUCN.  It is the most widespread monitor in the Indian subcontinent, which consists of most of its range.  Its population is decreasing in certain parts of its range due to hunting for skin.  Illegal pet trade is also a contributing factor.  It is now a protected species by many governments. 

Source of pic 2