We seem to be learning a lot about animal communication at present; from ear movement in horses to jackass penguin calls. Now, a team of researchers working in Brazil have found that river turtles communicate vocally, using various different sounds to synchronize social behaviors and look after young. The study has been published in Herpetologica.
During the nesting season, female Giant South American river turtles (Podocnemis expansa) clamber out of the Amazon River to dig holes and lay their eggs. During this time, these animals aggregate together and display various social behaviors that serve to exchange information and reduce predation. How they remain in a group during nesting, however, remained a mystery.
To find out more, researchers used microphones and underwater hydrophones to listen in on river turtles on the Rio Trombetas during the nesting period. They recorded the animals whilst they were active in 5 different behavioral patterns: migrating, aggregating, nesting, waiting after nesting and waiting for the arrival of the babies. Over a period of 3 years, the researchers captured 270 different sounds made by the turtles during 220 hours of recording.
After analyzing the vocalizations, which were all audible to the human ear, the researchers were able to categorize the sounds into 6 different types that all correlated with a specific behavior.
They found that sounds emitted while migrating or basking were generally low frequency, which likely helps to facilitate communication over longer distances. When the females were about to nest, however, the vocalizations were very varied. The researchers suggest that the turtles may be using these diverse sounds to synchronize movements and to decide on the specific nesting spot, but at this stage the exact meanings are unclear.
The scientists also discovered that hatchlings make noises both before they hatch and whilst they crawl out of the nest, which could possibly stimulate group hatching. The females then appear to respond to these calls with more vocalizations, which could possibly serve to guide the babies through the water.
“These distinctive sounds made by turtles give us unique insights into their behavior, although we don’t know what the sounds mean,” lead author Dr. Camila Ferrara said in a news-release. “The social behaviors of these reptiles are much more complex than previously thought.”
According to the researchers, this study provides the first pieces of evidence that turtles may use vocalizations to both coordinate group activities during the nesting season and to rear young. Unfortunately, this could therefore mean that these animals, which are threatened by unregulated consumption of their meat and eggs, are vulnerable to the effects of noise pollution. Understanding the behavior of these animals through studies such as this may therefore aid ongoing conservation efforts.