Dolphins may be among those animals sensitive to magnets, according to a recent study.

To determine if the marine mammals are magnetosensitive, or able to sense Earth's magnetic field, scientists at the Université de Rennes in France tested how six bottlenose dolphins in an aquarium reacted to a magnetized block.

Two barrels — one containing the magnetized block and another a demagnetized block — were placed in a pool.

Researchers ensured the barrels were identical so they would be indistinguishable to the dolphins, which use echolocation to locate objects by bouncing sound waves off them.

After the barrels were installed, the dolphins were allowed to swim freely in and out of the pool, and researchers observed that the dolphins approached the barrel containing the magnet much faster.

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

Scientists believe many animals — including birds, sharks, ants and cows — can sense magnetic fields.

Migratory birds use magnetic clues to find their way south in fall, for example, and a Baylor College of Medicine study concluded in 2012 that pigeons have magnetosensitive GPS cells in their brains.

Observations of migrating dolphins, porpoises and whales have suggested that the animals may be sensitive to geomagnetic fields, but little is known about how animals sense the Earth's magnetic field.

According to University of Illinois researchers, "The magnetic sense is maybe the last perception mechanism for which the nature of the receptors and of the biophysical mechanism remain unknown."

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