Data from: From parasitism to mutualism: unexpected interactions between a cuckoo and its host

Avian brood parasites lay eggs in the nests of other birds, which raise the unrelated chicks and typically suffer partial or complete loss of their own brood. However, carrion crows Corvus corone corone can benefit from parasitism by the great spotted cuckoo Clamator glandarius. Parasitized nests have lower rates of predation-induced failure due to production of a repellent secretion by cuckoo chicks, but among nests that are successful, those with cuckoo chicks fledge fewer crows. The outcome of these counterbalancing effects fluctuates between parasitism and mutualism each season, depending on the intensity of predation pressure.鸟类巢寄生者（Avian brood parasites）会将卵产于其他鸟类的巢中，由寄主亲鸟抚育这些非亲缘雏鸟，而寄主通常会因此损失部分或全部自身的雏鸟。然而，腐食性乌鸦（Corvus corone corone）却能从大斑凤头鹃（Clamator glandarius）的寄生行为中获益：寄生巢因杜鹃雏鸟分泌驱避性分泌物，降低了捕食引发的繁殖失败率；但在未被捕食的成功繁殖巢中，带有杜鹃雏鸟的巢所抚育出的乌鸦幼鸟出飞数量更少。这些相互抵消的效应所带来的最终结果，每年会在寄生关系与互利共生之间波动，具体取决于捕食压力的强度。