Even before facing daylight, baby crocodiles make a strange, yet interesting noise.

The sounds the infant reptiles produce more than a week before hatching may have two significant purposes, according to scientists: firstly, they serve as a clue to their siblings in the clutch that it is time to escape from their shells. On the other hand, the sounds may represent a signal for their mother. This way, she will be aware of the fact that hatching time is near and she will begin to dig the eggs out of the sand where she had buried them.

Some specialists show themselves skeptical about this hypothesis. Nicolas Mathevon of Jean Monnet University in Saint-Étienne, France stated that there were no “experiments testing the biological importance of this.”

Dr. Mathevon and Amélie L. Vergne do not share Mr. Mathevon’s opinion. They published an article in the journal Current Biology concerning the effects of pre-hatching calls. Their experiments were conducted at a crocodile-only zoo in the Rhône Valley, by monitoring Nile crocodile eggs that were due to hatch within 10 days.

The eggs were divided into three groups, for which the researchers either played recordings of pre-hatching calls, recordings of different other noises or no sound at all. The first responded very well while still being in their shells and they hatched more rapidly than the other two. Their mothers also began digging in response of their babies’ calls.

The only negative part of the infant crocs’ sounds is the fact that they can draw predators' attention, the researchers say. Therefore, it is important for all eggs to hatch at the same time, so that they aren’t neglected or excluded from maternal care.

The study was funded by the French Ministry of Research and the University Institute of France and published in the June 23 issue of Current Biology.