Dolphins can learn new language even while asleep

London - Scientists have found dolphins to be possessing such ability that they can learn a second language even while asleep.

According to scientists, captive dolphins in Port-Saint-Père, in France, have been recorded sleep-talking. But, as they rest at night, the aquatic mammals are not making dolphin sounds but whale-like noises, the Daily Mail reported.

Péos, Mininos, Cécil, Teha, and Amtan, the dolphins who were born in captivity, have only ever heard whale sounds as recordings, the Science magazine reported.

If the sounds were confirmed to be 'whale', it would be the first known instance of dolphins remembering a particular noise and repeating it later, say researchers.

These dolphins have only ever heard a whale sing on the soundtrack to their daily shows at the French aquatic park Planète Sauvage. The 21-minute tape, to which they perform, features several minutes of whale song among other marine noises.

A nine days and eight nights study, conducted between November 2008 and May 2009, revealed 25 occasions of never-heard-before dolphin sounds.

Researchers at the University of Rennes, France, hung underwater microphones in the performing dolphins' tank overnight, the Discovery reported.

The unusual noises -- which make up just one percent of all the sounds recorded -- strongly resemble whale song and occur only during 'rest periods,' mainly between midnight and 3 a.m.

Researchers recruited 20 volunteers to compare dolphin whistles and whale songs and found that the dophin's 'whale' is so good that listeners mistook it for real whale song 72 percent of the time.

The dolphins, the noises suggest, could be practicing their daily shows in their minds during night.