It is known that delphinidae can associate heard sounds with salient events/objects and mimic these sounds, mostly in the corresponding context. Thus, one can wonder whether dolphins, as other animals and humans, have a sort of sensory memory of events. Here we show that a group of five bottlenose dolphins in the Planète Sauvage dolphinarium (France) produced, during their nighttime resting periods, non-dolphin sounds that they heard during performance shows. In total, 3246 vocalizations were recorded during >120 hours (2588 vocalizations during >100 hours at day, 658 vocalizations during >20 hours at night). Generally in the middle of the night, these animals produced vocal copies of whale sounds that had been broadcast during daily shows. Recordings made before the whale sounds started being broadcast revealed that they have never emitted such sounds before. These unusual vocalizations differ from all other sounds in the dolphins’ repertoire. The similarity between the dolphins’ copies and the model whale sounds was substantiated by a discriminant function analysis with measured acoustic parameters and a playback experiment with human audience. This is to our knowledge the first evidence for the production of sounds heard during day salient events in a nocturnal resting context in marine mammals.