Science Story

02 December 2008 22:11 BST

Young crocodile messages revealed

Baby crocodiles still in their eggs signal to their mothers when they are ready to hatch, scientists have discovered.

The team from the Jean Monnet University and University of Paris also found that baby Nile crocodiles call to their siblings to ensure they all hatch at the right time.

Researchers thought this 'calling' system takes place from anecdotal evidence but today's study is the first to confirm the system through experiments.

The noises made by the crocodiles sound like "umph! umph! umph!" and are audible to humans.

To find out what those calls might mean, the researchers divided crocodile eggs that were due to hatch within ten days into three groups.

One of those groups was played recordings of pre-hatching calls; one was played recordings of noise; and the last was left in silence until they hatched.

The eggs played the pre-hatch sounds more often answered back.

Many of the eggs in that group also moved and all hatched during the playback or within ten minutes of it.

Only once did the eggs hearing noise hatch, and the rest hatched at least five hours after the last test.

To see how the mothers reacted to the different sounds, the researchers hid a loudspeaker underground near nests where eggs had been removed.

They then played pre-hatching calls interspersed with noise to ten mothers.

The adults more often turned their heads or moved after egg sounds than after noise and eight of the mothers responded to the recorded calls by digging.

Writing in the journal Current Biology, the researchers argue that the calling behaviour is probably critical to the early survival of the young crocodiles.

They said: "As birds also produce embryonic vocalisations that induce parental care, such acoustic communication at an early stage of development may be a shared behavioural feature of past and present Archosaurs [an ancient group of reptiles now represented by modern birds and crocodiles]."