Mother crocodiles lay eggs in a nest – often one that they return to year after year. They build the nest either in mounds of vegetation and mud or, like sea turtles, they dig a hole in the sand. For around 90 days, the momma crocs guard the nest from predators and other dangers. The nest acts as an incubator, keeping the eggs at a stable temperature that allows them to develop.
Unlike in most other animals, the sex of the young is not shaped by genetics; instead it is determined by the heat of the nest. If the sand or vegetation is a little warmer or colder at different layers it makes a difference in terms of how many males or females are born: males will be born at certain temperatures, females at others.
With as many as 40 eggs or more in a nest, there are a lot of babies-to-be for the mother crocodile to look after. Amazingly, the baby crocodiles ‘talk’ to their mothers while still in the egg. Researchers Vergne and Mathevon of Université Jean Monnet in Saint-Etienne, France showed that, just before hatching, they make “umph, umph, umph” noises – grunting sounds which act as a signal that they are ready to be born.
When the brother and sister crocs hear the sound, they start to ‘talk’ as well, and the mother croc comes to the nest to be ready for the births. The researchers discovered that whenever they played the high-pitched muffled sounds to the mother crocodiles, they started to dig in the sand – or guard the eggs if they were already out of the nest.
This is a unique survival mechanism, and it occurs because baby crocs are in danger from predators from the moment they have hatched. When they make their pre-birth noises, it’s to ensure that they all hatch in one batch and that they have their mother on hand to defend them.
During hatching the babies use an ‘egg tooth’ at the end of their snout that helps them to break the inner membrane of the egg and force their way out. Sometimes the mother will gently roll the eggs around in her mouth to help crack open the hard outer shell.
The mother crocodile doesn’t only guard the nest and babies before and directly upon hatching; she also protects them afterwards. The babies need to get to water for safety as quickly as possible, so mum takes them – often in her mouth – to a nursery area. Can you imagine carrying 15 babies in your mouth? Momma croc can! The skin of her lower jaw stretches to make a cradle for them.
The babies and adults continue to communicate after the birth, calling to each other into adulthood with up to 18 different sounds. That way, if a baby strays away from its group it can be guided back by the others or its mother can go to protect it. (Similar crocodilian maternal devotion can be seen in this sequence of photographs, in which a mother alligator prevents its baby from becoming a heron’s lunch.)
Contrary to what some might believe, mother crocodiles do not cannibalize their young but actively protect them before, during and after birth. However, one of the biggest dangers for the babies comes from other crocodiles. They will eat the young of other crocs, especially when the population is healthy and more babies aren’t necessary. When the population is low, though, this behavior lessens significantly. Maybe crocodiles really do care!