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.