River turtle mothers 'talk' to their hatchlings
Scientists in Brazil have managed to eavesdrop on underwater "turtle talk".
Their recordings have revealed that, in the nesting season, river turtles appear to exchange information vocally - communicating with each other using at least six different sounds.
This included chatter recorded between females and hatchlings.
The researchers say this is the first record of parental care in turtles. It shows they could be vulnerable to the effects of noise pollution, they warn.
The results, published recently in the Journal Herpetologica, include recordings of the strange turtle talk. They reveal that the animals may lead much more socially complex lives than previously thought.
The team, including researchers from the Wildlife Conservation Society (WCS) and the National Institute of Amazonian Research carried out their study on the Rio Trombetas in the Amazon between 2009 and 2011.
They used microphones and underwater hydrophones to record more than 250 individual sounds from the animals.
The scientists then analysed these vocalisations and divided them into six different types, correlating each category with a specific behaviour.
Dr Camila Ferrara, of the WCS Brazil programme, told BBC News: "The [exact] meanings aren't clear... but we think they're exchanging information.
"We think sound helps the animals to synchronise their activities in the nesting season," she said.
Sounds to guide
The noises the animals made were subtly different depending on their behaviour. For example, there was a specific sound when adults were migrating through the river, and another when they gathered in front of nesting beaches. There was a different sound again made by adults when they were waiting on the beaches for the arrival of their hatchlings.
Dr Ferrara believes that the females make these specific sounds to guide hatchlings to and through the water.
"The females wait for the hatchlings," she told BBC News. "And without these sounds, they might not know where to go."
Since many species of turtles live for decades, the researchers also think that young turtles might learn these vocal communication skills from older individuals.