Dolphins, already renown for their intelligence and range of abilities, can also sense whether an object is magnetized or not, researchers have found.

They may utilize this sensing ability to navigate over wide stretches of the open ocean using the magnetic field of the Earth, the scientists suggest.

In an experiment at a dolphinarium in France, when the smart cetaceans were presented with a range of objects -- some magnetic, some not -- they swam more quickly to investigate the magnetized ones.

A magnetic sense, known as "magnetoreception," has been detected in a number of species including bats, pigeons, turtles and insects, all of which may use it to orient themselves and navigate, says study co-author Dorothee Kremers of the University of Rennes.

There is evidence that migration paths of both dolphins and whales may be linked to our planet's magnetic field.

"Inside the ocean, the magnetic field would be a very good cue to navigate," Kremers says. "It seems quite plausible for dolphins to have a magnetic sense."

In the dolphinarium pool, the researchers watched the reaction of a group of bottlenose dolphins to floating barrels, some containing magnetized blocks and some with demagnetized ones, all of the same density and weight.

The barrels would have been indistinguishable to the dolphins' echolocation sense, where they bounce waves of sound off objects, so their preference for swimming toward and investigating the magnetic ones had to be down to a magnetic sense, the researchers reported.

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

The exact mechanism by which dolphins can detect a magnetic field isn't clear, she says.

Some scientists believe species capable of such a magnetic sense may possess tiny "ferromagnetic" particles within the cells of their body that are affected by a magnetic field, alerting the nervous system to such a field's presence.

Magnetic blocks used in the study at the Planete Sauvage dolphinarium were much stronger that the Earth's magnetic field, so more studies will be required to confirm if dolphins can use the globe's magnetism to navigate, the researchers say

Still, they say, the existence of a magnetic sense in dolphins has been confirmed.

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