Clueless but tactical: Random egg-tossing that protects against brood parasitism

Brood parasites exploit host species by replacing host eggs with their own, taking advantage of the hosts' parental efforts. In defense, hosts evolve to recognize and reject parasite eggs. Despite various cues potentially used by hosts to recognize parasite eggs, recognition can be difficult especially when parasites also evolve to mimic host eggs. If there are no reliable cues for recognizing parasite eggs, should hosts stop trying to reject them? Paradoxically, we show that it can still be beneficial for hosts to randomly reject a certain number of eggs from their nests, depending on the probability of parasitism. This seemingly irrational strategy for the hosts can be understood as a way to hedge their bets against potential parasites under sufficient uncertainty. Our results highlight how random decisions can emerge as an effective evolutionary tactic when information is limited.