A bottlenose dolphin (Dolly) swims to an underwater rig at Nuremberg Zoo, Germany, and rests her lower jaw on a bar. When she feels an electric field above her snout she leaves the station and swims to her trainer, who rewards here when she has correctly detected an electric field. When no electric field was presented, Dolly stayed with her jaw resting on the bar for 12s before visiting her trainer for a reward.

A view from inside the experimental rig that the dolphins use to indicate when they have felt an electric field. A dolphin (Dolly) swims to the rig and rests her jaw on a bar to position herself correctly. When she feels an electric field, produced by two small electrodes positioned above her snout, she leaves the station and swims to her trainer who rewards here when she has correctly detected an electric field.

A view from inside the experimental rig that the dolphins use to indicate when they have felt an electric field. A dolphin (Donna) swims to the rig and rests her jaw on a bar to position herself correctly. When she feels an electric field, produced by two small electrodes positioned above her snout, she leaves the station and swims to her trainer who rewards here when she has correctly detected an electric field.