Male bottlenose dolphins form first-tier alliances of two or three individuals to get and keep a female with whom one of the individuals in the alliance will mate. The males are competitive in this endeavour and they can rely on backup for help. If another male fails to help the first male can bear a grudge and not help that individual in the future.
This competitive behaviour is probably at least in part due to the fact that a female gives birth to one calf every five years. Demand is greater than the supply! This always creates heavy competition.
The first-to alliances are inside a second-tier alliance of a tribe of dolphins of about 14 individuals. Sometimes second-tier alliances group together to form a third-tier alliance. Once again the purpose is to get access to females and to defend against raiding parties.
Please click on the link above the photograph if you want to read more.