Bottlenose dolphins can distinguish between apparently identical objects made from different materials using echolocation alone. An international study conducted at Loro Parque in Tenerife and published in The Journal of the Acoustical Society of America has examined how dolphins combine biosonar and movement to investigate their surroundings while swimming.
The research, carried out by scientists from the University of Southern Denmark and Loro Parque Fundación, involved Achille and Clara, two bottlenose dolphins (Tursiops truncatus) living at the park. The dolphins were trained to swim towards pairs of spheres suspended in the water and select the one made from the correct material using sound alone.
Although visually identical, the spheres were made from different materials, including plastic, aluminium, brass and steel. By producing ultrasonic clicks and analysing the echoes returning from the objects, dolphins can obtain information about their characteristics and build a representation of their surroundings.
Using highly sensitive hydrophones and synchronised underwater cameras, the researchers were also able to document what happened in the fractions of a second before each decision. The dolphins oriented their heads, changed their swimming trajectories and adjusted their echolocation clicks as they approached the objects.
“We have been able to discover that dolphins actively adjust their movements and sound production to ‘see’ the composition of objects while swimming,” said Sara Torres, the scientist leading the project. “It is fascinating to see how Achille and Clara use their clicks to obtain detailed information about what surrounds them. This basic knowledge is fundamental to understanding how changes and noise in the aquatic environment affect cetaceans, and it allows us to develop much more effective conservation measures adapted to the biology of each species.”
The study also compared bottlenose dolphins with harbour porpoises under the same experimental protocol. Both species displayed similar active exploration strategies, turning their heads and altering their swimming trajectories to scan the target. However, differences in the frequency and structure of their acoustic signals resulted in different discrimination capabilities.
The comparison provides new clues as to how evolution has shaped the sonar systems of different cetacean species according to their biological needs and the acoustic environments in which they live.
The findings may also have implications for conservation in the wild. Understanding in greater detail how cetaceans use sound to perceive and interpret their surroundings can help scientists assess how human-generated underwater noise may interfere with essential behaviours, including finding food, navigating and communicating.
“This study reaffirms our unwavering commitment to science and the protection of biodiversity. At Loro Parque, we not only care for our animals according to the highest welfare standards, but also open our doors to the international scientific community to generate knowledge that is vital to saving the oceans,” said Wolfgang Kiessling, President of Loro Parque Group.
“Without the close collaboration between our team of experts and the researchers, discoveries of this magnitude simply could not be made,” Kiessling added.
The research was published in The Journal of the Acoustical Society of America (JASA) and involved the University of Southern Denmark (SDU) and Loro Parque Fundación. The work was funded by the Office of Naval Research, the Human Frontier Science Program and the Carlsberg Foundation.
