Researchers have now discovered what has long been known about sharks and rays in behavioral experiments on the bottlenose dolphin: the dolphins (Tursiops truncatus) can perceive electric direct current fields and react accordingly. This not only helps them search for fish hidden in the seabed sediment. There are also important clues about the orientation behavior of bottlenose dolphins in the world’s oceans, writes a team of biologists and physicists from Rostock and Nuremberg in the journal “Journal of Experimental Biology”.

The experiments have shown for the first time that bottlenose dolphins have a sensory basis for using the earth’s magnetic field for orientation, said neurobiologist Guido Dehnhardt from the Institute of Life Sciences at the University of Rostock. At least the potential for it is there. “It is fair to say that dolphins have this ability.”

The research team includes first author biologist Tim Hüttner (University of Rostock/Tiergarten Nuremberg), physicist Lars Miersch (University of Rostock) and Lorenzo von Fersen from Tiergarten Nuremberg.

Phenomenon known in only a few mammals

So-called electroreception has been known for a long time in sharks and rays. “The shark is an absolute electrical specialist among marine animals,” says Dehnhardt. Among mammals, electroreception has so far been demonstrated in the platypus, the short-beaked echidna and, in 2012, the Guiana dolphin. And now also with the bottlenose dolphin.

Animal subjects “Dolly” and “Donna”

The new findings were based on experiments with the dolphins “Dolly” and “Donna” at the Nuremberg Zoo, which has been keeping dolphins since 1971. There, the animals in the dolphinarium first learned to swim underwater into an experimental apparatus made of PVC pipes in order to remain there. They placed their snouts on a shelf. If there is an electrical signal, they should leave the apparatus again. If there was no signal, they should wait in the apparatus for at least twelve seconds. Right decisions were always rewarded with a fish.

The animals perceived the electric fields via nerve-rich so-called vibrissae pits on their upper beaks. Young animals have small tactile whiskers (vibrissae) that help them with the not so easy task of finding their mother’s teat. The experiments also revealed that Dolly and Donna reacted slightly differently depending on the strength of the electric fields. “But that was marginal,” said Hüttner.

Lots of training in advance

Before Donna and Dolly were ready, the researchers and the team of trainers led by dolphin keeper Armin Fritz had to invest a lot of time. Donna and Dolly trained for one to a half years until the measurements with electric fields could begin. “It involved very, very weak direct current fields that cannot be perceived without proper receptors,” says Hüttner. “I put my hand under it once. Nothing happened.”