Male whales can produce complex songs lasting tens of minutes during breeding season. The songs often include rhyme-like repeating elements. At a given time all whales in a group typically sing almost the same song, which gradually changes. The function of the song is quite unclear. It has been claimed that its frequencies are optimized for long-range transmission in the ocean, but this appears not to be the case. In dolphins, it is known that one dolphin can produce patterns of sound that are repeated by a specific other dolphin.