For some time it's been suspected that wild cetaceans (whales, dolphins and porpoises) can detect the Earth's magnetic field and use it to help them navigate. In fact, one theory for why cetaceans sometimes swim on to a beach and strand themselves is that a nearby source of magnetism is confusing their navigation system. Now researchers in France have discovered that captive bottlenose dolphins behave differently when they are near a magnet compared to their behaviour when no magnet is nearby, which adds support to the idea that cetaceans are magnetosensitive.
Researchers at a university in Rennes placed a block inside a barrel and placed the barrel in the water of a dolphin tank. The block was either unmagnetized or strongly magnetized. All the barrels used in the experiment had the same density and would have given the same information to the dolphins as they explored them by echolocation. Echolocation is the system in which cetaceans release sound waves that bounce off an object and return, giving the animal detailed information about the object.
The dolphin habitat consisted of four connected pools. The six animals were free to move in or out of the pool containing the barrel as they wished. Their reaction to the barrel was observed and recorded.
Neither the person who put the barrel in the water nor the person who analyzed the videos showing the dolphins' behaviour knew whether the block in the barrel was magnetized or unmagnetized. This precaution was taken to prevent people from giving accidental signals to the dolphins as they approached the barrels. It also prevented the person analyzing the video from unconsciously interpreting the animals' behaviour in a way that supported their preferred outcome.
The researchers found that the dolphins approached the barrels with a magnetized block much faster than the ones containing an unmagnetized block. This suggested that they detected something different about the magnetized barrels and that this difference attracted them. The dolphins didn't interact with the blocks differently, though. Still, the evidence suggests that bottlenose dolphins are another animal to add to the growing list of magnetosensitive organisms.