London - Dolphins are sensitive to magnetic stimuli, as they behave differently when swimming near magnetised objects, a new study has found.

The research by Dorothee Kremers and her colleagues at Ethos unit of the Universite de Rennes in France provides experimental behavioural proof that these marine animals are magnetoreceptive.

Magnetoreception implies the ability to perceive a magnetic field. It is supposed to play an important role in how some land and aquatic species orientate and navigate themselves, researchers said.

Some observations of the migration routes of free-ranging cetaceans, such as whales, dolphins and porpoises, and their stranding sites suggested that they may also be sensitive to geomagnetic fields.

Because experimental evidence in this regard has been lacking, Kremers and her colleagues set out to study the behaviour of six bottlenose dolphins in the delphinarium of Planete Sauvage in Port-Saint-Pere in France.

They watched the animals' spontaneous reaction to a barrel containing a strongly magnetised block or a demagnetised one.

Except from this characteristic, the blocks were identical in form and density. The barrels were therefore indistinguishable as far as echolocation was concerned, the method by which dolphins locate objects by bouncing sound waves off them.

During the experimental sessions, the animals were free to swim in and out of the pool where the barrel was installed.

All six dolphins were studied simultaneously, while all group members were free to interact at any time with the barrel during a given session.

The person who was assigned the job to place the barrels in the pools did not know whether it was magnetised or not. This was also true for the person who analysed the videos showing how the various dolphins reacted to the barrels.

The analyses revealed that the dolphins approached the barrel much faster when it contained a strongly magnetised block than when it contained a similar not magnetised one.

However, the dolphins did not interact with both types of barrels differently. They may therefore have been more intrigued than physically drawn to the barrel with the magnetised block.

"Dolphins are able to discriminate between objects based on their magnetic properties, which is a prerequisite for magnetoreception-based navigation," said Kremers.

"Our results provide new, experimentally obtained evidence that cetaceans have a magnetic sense, and should therefore be added to the list of magnetosensitive species," Kremers said.

The study was published in Springer's journal Naturwissenschaften - The Science of Nature. (PTI)