Sydney, Mar 29 (IANS): Male dolphins are not only gregarious, they also form complex alliances with their close kin and friends, says a study.

Groups of two to three males form "first-order" alliances that involve close relatives, such as cousins, cooperating to guard or act as consorts to females.

Long-running studies by many researchers at Shark Bay, Western Australia, have revealed that these small groups may persist for up to 20 years, the journal Proceedings of the Royal Society B reported.

"Sometimes one of these first-order alliances is seen to assist another to gain access to a female, but on another day the same two groups may be opposed in a contest over a female," said New South Wales geneticist and study co-author Bill Sherwin.

Teams of four to 14 males cooperate in "second-order" alliances to attack other alliances and to defend against such attacks, said a university statement.

Second-order alliances can persist intact for over 15 years and may be considered the core unit of male social organisation in Shark Bay, the researchers say.

Finally, two or more "second-order" groups may team up from time to time to form a "third-order" alliance. The study tackled the question of how they choose to make these alliances.

Srdan Randic's team was able to exclude the so-called "community defence model" used by chimps, for example, in which semi-closed communities (ones that occasionally accept new members emigrating from other groups) are defended by males ranging across their group's entire range.

Randic is a master's student at the University of Massachusetts, who led the study. It was supervised by Richard Connor, research fellow at the University of New South Wales.