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Crocodiles - How they grow from egg to adult

Updated on October 2, 2010

Crocodiles are fantastic creatures, and can grow to be the biggest reptiles around. However they are being threatened by human civilization, as we encroach on their territories and chase them out. Crocodile conservation should be a top priority in the regions in the world where they still live. They have been around since the dinosaur era, and have evolved to perfection. They are the ultimate killing machines. But every big croc was once a small baby, so let’s take a look at how they grow so big.

Nest mounds and holes for the eggs

Crocodiles are sexually mature around 6 years of age. The mating season usually start around the monsoon time or the wet season. Every male has its own territory, usually with one or more females living in it with him. When the female comes into season, she will initiate the mating and let the male know she is ready by holding her head high out of the water, growling, and producing a stimulating scent from two small glands under her throat. This is followed by synchronized swimming by the pair, until the female allows the male to mate with her.

When the female is fertilized and she has her eggs developing, she finds a suitable place to build a nest. It has to be a place close to the water, but dry, and the temperature should be just right. Sometimes a crocodile comes back to her nest site every year, if it was successful in the past. Once she has picked a good spot, she will build her nest. She does this by using the surrounding vegetation to build a large mound with her back feet. To make sure it is perfectly round, she uses her tail. She drapes it over the nest from all sides to ensure good shape. Once she is finished she will lay her eggs in the mound. Some species makes holes. They dig deep holes in the sand of the banks with her back feet. She then lays her eggs and covers the hole up again.

The female crocodile will lay about 80 to a 100 eggs. She will guard them furiously, and this is the most dangerous time to be around crocodile territory. She will be very aggressive and attack everyone and everything that comes near. And since crocodile eggs are a delicacy to several other animals, thieves are always on the prowl. Especially goannas enjoy them greatly. The eggs need a temperature between 30 to 32C to incubate properly for up to 90 days. During this time the female will try to be at the nest at all times, and often doesn’t feed as much as she usually would. The sex of the babies is not predetermined, but depends on the temperature in the nest. At around 31,6C it will be all boys, temperatures slightly higher or slightly lower will ensure girls only.

From baby to adult

When the eggs start hatching, the baby crocodiles make little noises, so the female will open the mound or dig them out of their hole. She will gently crack open the eggs that haven’t hatched yet, and then she carries the babies to the water in her mouth. Here she will protect them for another few weeks, up to two months. After that she will lose interest and the babies are out on their own.

This is a crucial period for the babies, as they are still small (about 20 cm long) and therefore vulnerable. They have to watch out not to get eaten by bigger fish, and even bigger crocodiles, like their dad. They live on small fish, and expand their diet as they grow bigger to rodents, birds, and eventually bigger prey like springboks and gazelles.

After they’ve grown too big to share a territory with their dad, they disperse and go out to find a spot of their own. They generally look for places with a high availability of food, riverbanks for warming up in the sun, and no competition, or competition they can handle and drive out. Here they will settle and stay for long times. Crocodiles who have been relocated, have been known to swim for kilometres and travel for days or weeks to get back to their homes. This is where they will start a family of their own and grow old comfortably, that is if they aren’t chased out by bigger crocs or humans. Their life expectancy is comparable to that of humans, and is on average about 80 years, but they can get as old as a hundred.

Size and length

When they are born they are just a couple of centimetres long, but they can grow to be several metres long. The babies will grow about 30 cm per year until they become adults. After that the growth in length slows down, but they continue growing in width. They will continue growing for their whole life, and they can get to an age of about 100 years. Crocodiles in captivity, which are being fed regularly and well looked after, can become massive in length and width. The biggest crocodile ever caught was over 7 metres long, and weighed over 1,5 tons. Half of their length is their tail, and the other half the rest of their body. The males grow faster than the females, and they also grow larger.


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      Phyllis 7 years ago

      Awesome article very informative!!