ZooNooz Article - September 2003

Seeing sound

Do Leopard Seals use echolocation to find their way around their icy underwater world? MICHELLE LINDSAY reports on research which may provide the answer to one of nature's most perplexing questions.

Photographs Jo Nevin

A question which has persistently baffled researchers is how different animals hear and interpret their world. One thing we know is that some species use a process called echolocation to listen and find their way around.

Echolocation involves animals producing short sounds such as clicks, shrills and whistles. Many of these sounds are ultrasonic so cannot be detected by the human ear. When the sound waves hit an object, some of the sound is bounced back and picked up by the animal. By analysing this echo, the animal is not only able to identify objects that are in its path but also to work out how big and how far away an object is.

Leopard Seals

It is well documented that some animals, including bats, dolphins, porpoises and some species of whales and birds, have the ability to use echolocation to decipher their world. They can orientate themselves in their surroundings, identify obstacles, detect other members of the same species and locate food. Research is currently being carried out at Taronga Zoo by the Australian Marine Mammal Research Centre (AMMRC) and the Marine Mammal Division to see if another animal can be added to the list - the Leopard Seal.

Until now, marine scientists have had to speculate about much of the underwater behaviour of Leopard Seals. We know they predominantly use eyesight and smell to decipher their frosty Antarctic environment, and both male and female Leopard Seals are able to produce a wide range of sounds including some of very high frequency. There is a strong suggestion that they use these very high-frequency sounds to echolocate, but there has been limited research conducted to either verify or discount this theory.

Ady signals to ask Brooke if the ball is in the box. Brooke responds by going to either the 'Yes' or 'No' paddle.

In an attempt to provide an answer, Marine Mammal keepers Jo Walker, Ady D'Ettorre and Andrew Barnes, together with the team from AMMRC, spearheaded by Dr Tracey Rogers and including Carolyn Hogg, Sebastian Spencer and Joy Tripovich, have implemented a positive reinforcement training schedule with Taronga's Leopard Seal, Brooke.

The experimental technique involves submerging a perspex box one metre below the surface of Brooke's pool. To start with, the box will be completely see-through, but eventually the sides will be darkened and Brooke will be unable to see into it. There are two paddles on either side of the box with one paddle representing "Yes" and the other "No". Brooke's task is to indicate to keepers and researchers whether a ball has or has not been placed inside the box. The paddles are fitted with lights and electronic equipment which not only record when Brooke has touched the paddle but also whether she has provided the correct answer. Behind the box will be an array of hydrophones which can detect highfrequency sounds.

It is already known that sight is the predominant sense used by Leopard Seals and, with the clear perspex box, Brooke is not required to use any other sense to discover whether there is something inside. However, cover the perspex panels and Brooke will be unable to see inside the box. Will she be able to indicate to trainers if a ball is present or not? In other words, will she be able to detect an object in the box if she is not able to see it?

If Brooke is able to indicate to trainers that a ball is or is not present inside the box and if there are positive readings on the sound recording equipment, this should go some way towards proving that Leopard Seals do use their high frequency sounds to echolocate.

Jo sends Brooke to the next-door pool while researchers set up another task.

Marine Mammal keeper Andrew Barnes said staff have been involved in training Leopard Seals in the past and are particularly happy with how Brooke is responding. "I think this is because we now have a much clearer idea of what our final goal is and can see most of the steps along the way that we can use to help Brooke understand where we are going," he says.

While it is still too early in the project to either verify or discount the echolocation theory, researchers and keeping staff have been delighted with early results. Perhaps one of the most exciting components of this research is that zoo visitors will soon be able to watch keepers carry out their training sessions with Brooke and gain firsthand understanding of this groundbreaking research.

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