Siren juveniles can often test one another in hunting, combat, and evasion skills whilst the adults are out and about. Older sirens have a tendency to lord over younger 'brothers' whether or not they are of the same parents. Sirons take many years to develop the proper muscle coordination and strength to serve the pack properly, so it serves them beneficially to have an superior remind them of it. For a pack with weak males has no chance of defending against a dragon or any destructive monster lurking in wait.
Wrestling is a very widespread custom in which a 'sister' and a 'brother' attempt to pin the other's head into the ground for ten seconds, the first to subdue wins. Every now and then a unique siron develops quicker than others his age and can win a few matches, thus putting him in the eyes of the Matriarch for a potential alpha in development. Good genes and a large population can lead to the creation of a splinter pod which with its own Matriarch chosen by the former will then head off to find its own territory. Much in how beehives reproduce, as this helps diversify the blood by opening up room for wandering sirens to join the pod.