Fatal mobbing and attack of the common cuckoo by its warbler hosts

Nest defence is an effective strategy of hosts against parasites. Typically, hosts will aggressively attack brood parasites that approach or visit their nests, which can prevent the parasites from laying eggs or may even lead to the death of the parasites. Few previous studies have specifically reported such fatal cases involving brood parasites and have attributed the cause of death to either drowning or hypothermia after falling into the water following an attack from hosts. In this study, we recorded the process of multiple host individuals of the Oriental reed warbler (Acrocephalus orientalis) mobbing and attacking a female common cuckoo (Cuculus canorus) in the field. We discovered that the immediate cause of the cuckoo’s death was the fatal physical damage resulting from the aggressive defence from the hosts, suggesting that frantic pecking and scratching by the hosts is the most proximate cause of mortality among egg-laying female cuckoos. This finding enhances our essential understanding of the effectiveness of host attacks.

巢防御是宿主对抗寄生生物的有效策略。通常而言，宿主会主动攻击靠近或造访其巢穴的育雏寄生生物（brood parasite），此举既可阻止寄生生物产卵，甚至可直接导致寄生生物死亡。此前鲜有研究专门报道此类涉及育雏寄生生物的致死案例，且多将死亡原因归因于宿主攻击后寄生生物落入水中，进而引发溺水或体温过低。本研究野外记录了多只东方大苇莺（Acrocephalus orientalis）个体聚众围攻并攻击一只雌性普通杜鹃（Cuculus canorus）的全过程。我们发现，该雌性杜鹃的直接致死原因是宿主攻击性防御所造成的致命物理损伤，这表明宿主疯狂的啄击与抓挠是产卵雌性杜鹃死亡的最直接诱因。该发现深化了我们对宿主攻击行为有效性的核心认知。