Sound communication and Nile’s Crocodiles

Wednesday, August 22nd, 2007

Amélie Vergne, student in the ENES laboratory (ecology and sensorial Neuro-ethology) of Saint Etienne, and Nicolas Mathevon, her supervisor (Teacher in Jean Monnet University and member of the university institute of France) made researches with the teams of La Ferme aux Crocodiles about vocal interactions between crocodiles.

A part of Amélie’s work is about the noises made by the young crocodiles, while they still are in the egg. To determinate the role of those noises, the work done is built in two steps:

1) A work in laboratory

Amélie brought about 40 crocodiles eggs from different females in her laboratory. The eggs are supposed to hatch at the same time. In order to know if the shouts pre-hatching help in the birth process, the eggs were separated in three groups.

The experience’s results showed that the hatching noises activate strong responses with young crocodiles: a vocal signal until the complete hatching.

2) A work at La Ferme aux Crocodiles

Wednesday 18th and Thursday 19th, 2007, Amélie and her supervisor were at La Ferme aux Crocodiles to determinate the impact of pre-hatching noises on adults crocodiles.

The experience was realized on 10 females which had laid three months earlier. The crocodile mothers bury their eggs in the sand, in a place they strongly defend. The team of La Ferme aux Crocodiles usually, takes the eggs after the laying, in order to put them in incubators. Nevertheless, mothers stay near by their nest and are still aggressive.

It was the case of the 10 females selected for the experiences. In the middle of July, they should expect their babies’ birth. In order to exactly know the role of the pre-hatching shouts, scientists realized playback experiences. A loudspeaker broadcasting sounds was buried in the sand, in the place of the nest.

Amélie and Nicolas chose to broadcast to each female and in a random order, two series of signals.

The first one is constituted by hatching shouts, recorded in the incubator.

The second one is constituted by a succession of noises which have no biological meaning for the female.

Eight females reacted immediately to pre-hatching shouts. During the 10 minutes of the playback, the scientists were able to observe the female digging the sand very delicately. Those females never react in response to the noising playback.

For the two remaining females, one - doubtless little motivated answered on none of both signals and one - very motivated dug in both cases!!

Even if a precise treatment of results is necessary, it seems that the shouts of hatching carry real information inferring a strong behavioral answer of the mother.

This behavior is exceptional with reptiles. It’s the first time that researchers show by a scientific experience the role of shouts of hatching with the females.

It still remains a lot of works to do to understand better the vocal interactions with crocodiles.

Follow the future experiences…

To learn more about scientific works of the ENES team, you can visit Amélie’s website: http://amelie.vergne.googlepages.com/

The team of La Ferme aux Crocodiles was pleased to welcome Amélie and Nicolas. Don’t forget that La Ferme aux Crocodiles is a touristic site, but its vocation is also to protect and help in conservation of crocodile species. That’s why we want to act in scientific researches and we built a laboratory in 1998.

Nowadays, we still are collaborating with scientists from the whole world.