3) the Salt-water crocodiles.
The biggest and the most dangerous of all crocodiles in the world is the salt water crocodile, which can grow upto 25 feet. It is the only crocodile that can live in the sea for a long time. The Nile crocodile of Africa is yet another deadly species. Fossils of three other extinct species of crocodiles have also been found in India.
These cold blooded animals have evolved with dinosaurs millions of years ago and are more closely related to birds than to snakes or reptiles. Being cold blooded they control their body temperature by seeking shady, sunny spots or different levels in water. They often bask with their jaws open, which probably helps them to keep cool.
Their eyes, nose and ears are positioned in a straight line along with head and snout. They have good eyesight and a good sense of smell, and can hear very well. Their tail is very strong and helps them in swimming. They have a very low metabolic rate and thus need to hunt only every few days. They can decrease their metabolic rate and stay under water for a long time. Alligators have been known to stay under water for upto 6 hours. They do not make any unnecessary movements but can move very fast even on land when necessary. Small salties can gallop at a speed of 48 kph for short distances.
Crocodiles are found in large and small rivers, lakes, mangroves, and in brackish and fresh water. When a baby crocodile hatches, it is just about three quarters of a foot (25-30 cms) in length. In a few years it matures into an adult. Maturity depends upon size rather than on age. Generally males mature slower than females.
In the wild, a female will take between 5-7 years to mature whereas males will take 9-11 years. Gharials take longer to mature; about 8-10 years for the female and 12 years for the male. In captivity, such as in the Madras Crocodile Bank, females mature in four years and males in five.
The average size for maturity for a Mugger is-male (2 metres) and female (1.6 metres). Males of Gharials and Salties mature at three and a half metres and females at three metres.
Mugger crocodiles breed in between February and April. Salties breed in
April and Gharials between the last week of March to the second week of
April.
Breeding depends on environmental conditions. In the breeding season males often fight for the right to court with several females. During courtship each pair may blow bubbles, rub noses, raise their snout and periodically submerge and re-emerge. Different species show different courtship displays. Gharials, for example, often court each other by making a loud buzzing sound. Mating occurs under water with the male mounted on top of the female.
The average gestation period is between 35-60 days. The gestation for a Mugger is 35-40 days and for Gharials and Salties, 40-65 days. The temperature at which eggs are incubated and the moisture content of the environment (humidity) influence the sex within the embryo.