Baby crocodiles tell each other when to hatch

To the human ear they sound like the tinny thud of a small starter motor, but to a mother crocodile they are the plaintive calls of her egg-bound babies, saying they are about to hatch en masse and could she please make sure there are no nasty predators nearby.

The "umph, umph, umph" calls of unhatched crocodiles have been shown by scientists to be vital vocal signals that co-ordinate their entry into the world.

For the first time, researchers have shown that the pre-hatching calls of baby Nile crocodiles actually mean something to their siblings – and to their mothers.