Arabian Babblers
First of all, babblers compete to help each other and the group—often aggressively so. For example, not only do higher-ranked babblers give food to lower-ranked babblers, sometimes they force it down the throats of unwilling birds! Similarly, when a beta male is standing guard duty at the top of the tree, the alpha will often fly up and harass the beta off his perch. The beta, meanwhile, isn't strong enough to bully the alpha from guard duty, but he will often stand insistently nearby, offering to take over if the alpha male allows it. Similar jockeying takes place for the "privilege" of performing other altruistic behaviors. ...
The alpha male ... almost never tries to replace the gamma male from guard duty; instead the alpha directs all of his competitive energies toward the beta. ...
Even more damning is the fact that babblers often interfere in the helpful behaviors of their rivals, for example, by trying to prevent them from feeding the communal nestlings. This makes no sense if the goal is to benefit the group as a whole.
So if these activities aren't altruistic, what's the point? What's in it for the individual babbler who competes to do more than his fair share of helping others?
The answer, as Zahavi and his team have carefully documented, is that altruistic babblers develop a kind of "credit" among their groupmates—what Zahavi calls prestige status. This earns them at least two different perks, one of which is mating opportunities: Males with greater prestige get to mate more often with the females of the group. A prestigious alpha, for example, may take all the mating opportunities for himself. But if the beta has earned high prestige, the alpha will occasionally allow him to mate with some of the females. In this way, the alpha effectively "bribes" the beta to stick around.
The other perk of high prestige is a reduced risk of getting kicked out of the group. If the beta, for example, has earned lots of prestige by being useful to the group, the alpha is less likely to evict him. Here the logic is twofold. First, a prestigious beta has shown himself to be more useful to the group, so the alpha prefers to keep him around. Second, by performing more acts of "altruism", a babbler demonstrates his strength and fitness. An alpha who goes beak-to-beak with a prestigious beta is less likely to win the fight, and so gives the beta more leeway than he would give a beta with lower prestige.
