If a restaurant owner fails to pay the 'protection money' demanded of him by the mob, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to make restaurant owners pay up. Similarly, mafia-like behavior is observed in parasitic birds, which lay their eggs in other birds' nests. If the host birds throw the cuckoo's egg out, the brood parasites take their revenge by destroying the entire nest. Consequently, it is beneficial for hosts to be capable of learning and to cooperate. Previously seen only in field observations, scientists have now modeled this behavior mathematically to confirm it as an effective strategy.

Source: Fear of the cuckoo mafia: In fear of retaliation, birds accept and raise brood parasites' young