London, Aug 17 (IANS): In a first instance of recorded parental care in turtles, scientists have found that these reptiles use sound to stick together and care for young.

Scientists working in the Brazilian Amazon have found that giant South American river turtles actually use several different kinds of vocal communication to coordinate their social behaviours, including one used by female turtles to call to their newly-hatched offspring.

"These distinctive sounds made by turtles give us unique insights into their behaviour, although we do not know what the sounds mean," said Camila Ferrara, an aquatic turtle specialist for the Wildlife Conservation Society's Brazil Programme.

The research team captured 270 sounds during 220 hours of recording with both microphones and hydrophones when the turtles were swimming through the river.

Sounds made by the turtles while migrating through the river or basking tended to be low frequency sounds.

Vocalisations made during nesting tended to be higher frequency sounds, possibly because higher frequency sounds travel better in shallow water and in the air.

The highest diversity of sounds are used by females about to nest. The researchers theorise that the animals use these sounds to decide on a specific nesting site and to synchronise their movements.

The hatchling turtles themselves make sounds before they hatch and continue to do so as they clamber out of the nest chamber on the river bank.

The sounds may stimulate group hatching.

"The females, in turn, vocalise in response to the nestling calls, perhaps guiding the nestlings into the water," Ferrara noted.

Using sonic transmitters, the team also discovered that the hatchlings remain together and migrate with adult females for more than two months.

The study appeared in the journal Herpetologica.