According to the Australian researchers who have picked up "dolphinese", the language shows the animals are more similar to humans that previously thought.

The scientists identified almost 200 different whistles that the dolphins make to communicate, and linked some to specific behaviours.

Biologist Dr Liz Hawkins and her colleagues listened to the chatter of wild bottlenose dolphins off the western coast of Australia for three years.

Dr Hawkins, of the whale research centre at Southern Cross University, New South Wales, said: "This communication is highly complex, and it is contextual, so in a sense it could be termed a language."

Dolphins were known to use "signature" whistles to identify themselves to others, but the meaning of the other whistles they make was a mystery.

Dr Hawkins recorded 1,647 whistles from 51 different groups of dolphins living in Byron Bay, New South Wales.

The biologist, who presented her work at a meeting of the Society for Marine Mammalogy in Cape Town, grouped all the whistles into five tonal classes and found that these groups, and even individual whistles, clearly went with different behaviours.

Dr Melinda Rekdahl, of the University of Queensland in Brisbane, said it was too early to know whether whistles might mean something specific, but added: "It is possible. Dolphin communication is much more complicated than we thought."

The research, the scientists claim, will lead to a reassessment of the social complexity of dolphins, raising moral questions over how those kept in captivity should be treated.

Researchers have been studying the bottlenose dolphins (Tursiops sp.) in Shark Bay, Western Australia for quite a long time because they are tame. They have observed male-male alliances that seem very stable. Male alliances are usually groups of two or three males that can last many years. The association coefficient for some pairs of males is in the same range as those found for mothers and their nursing calves(3).

So why do males form these alliances? The answer seems to greatly reflect human behavior: to get women. Male alliances typically "herd" females for anywhere from a few minutes to months(4) These herding events are not usually enjoyed by the females. Herding is often forcible with escape events and violence involved.(3) In a herding event males will surround the female or chase her. Aggression toward the female is common and can include: hitting with the tail, head-jerks, charging, biting, or body slamming.(3) Should the female try to escape, which often happens, the males will chase her more often than not. Of course the ultimate goal of a herding event is sex and the males in the alliance will take turns to make sure everyone has an equal share. If the alliance has three members, only 2 will herd the female and the third will stay behind. However, the individual who is left behind changes with every herding event so again all members have an equal chance at mating. (3)