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Populations of male humpback whales undergo a "cultural revolution" every few years when they change their song anthem, according to new research.

A 13-year study involving experts from the University of St Andrews found the signature song of individual groups evolves gradually over time.

However every few years, a population's song is completely replaced in an event described as a "cultural revolution".

When the revolutions occur the new song is always simpler than the one before.

Humpback whales are famed for having "dialects" unique to different populations.

In addition, groups of male whales have their own "anthems", with each member of the population singing the same sequence of the same sounds.

The new research was carried out by academics at the University of St Andrews and the University of Queensland in Australia.

It focused on 95 humpback whale "singers" from east Australia and found evidence that gradual song changes were due to embellishments introduced by individuals that were then learned by the rest of the group.

The scientists said songs introduced by revolutions may have been simpler because the singers found it harder to learn completely new material.

Dr Jenny Allen, of the University of Queensland, said: "The consistent reduction in complexity during song revolutions suggests a potential limit to the social learning capacity of novel material in humpback whales."

The research is reported in the journal .