Hawk mimicry does not reduce attacks of cuckoos by highly aggressive hosts

Laikun Ma,Canchao Yang,Wei Liang

doi:10.1186/s40657-018-0127-4

Abstract

BackgroundResemblance to raptors such as hawks (Accipiter spp.) is considered to be an adaptive strategy of cuckoos (Cuculus spp.), which has evolved to protect cuckoos against host attacks. However, the effectiveness of the mimicry remains controversial, and is not yet fully studied for highly aggressive hosts.MethodsWe evaluated the effectiveness of sparrowhawk (Accipiter nisus) mimicry by common cuckoos (Cuculus canorus) in oriental reed warblers (Acrocephaus orientalis), which are highly aggressive hosts. Using a both the single and the paired dummy experiment, defense behaviors and attack intensities of oriental reed warblers against common cuckoos, sparrowhawks and oriental turtle doves (Streptopelia orientalis) were assessed.ResultsOriental reed warblers exhibit strong nest defense behaviors, and such behaviors do not change with breeding stage (i.e., egg stage and nestling stage). Furthermore, assistance from conspecific helpers may increase attack intensities. However, they were deterred from mobbing overall by the presence of the hawk.ConclusionsOriental reed warblers are able to distinguish cuckoos from harmless doves. However, they may be deterred from mobbing by the presence of the predatory hawk, suggesting hawk mimicry may be ineffective and does not reduce attacks of cuckoos by highly aggressive hosts.

Highlights

Resemblance to raptors such as hawks (Accipiter spp.) is considered to be an adaptive strategy of cuckoos (Cuculus spp.), which has evolved to protect cuckoos against host attacks
All oriental reed warblers performed for single dummy experiments showed strong nest defense behaviors, and 90% (28/31) of the oriental reed warblers attacked the dummies
The main findings of this study were that oriental reed warblers displayed aggressive nest defense behaviors with more than 90% of the warblers demonstrating strong attack behaviors towards intruders, and their nest defense behaviors did not differ between egg laying, incubation, and nestling stages

Summary

Introduction

Resemblance to raptors such as hawks (Accipiter spp.) is considered to be an adaptive strategy of cuckoos (Cuculus spp.), which has evolved to protect cuckoos against host attacks. The high costs of successful cuckoo parasitism have forced hosts to evolve counter-adaptive strategies in different stages. The competition between hosts and brood parasites during the egg laying and incubation stage has received much attention. Many hosts demonstrate strong aggressive nest protection behaviors against cuckoos approaching the nests, to prevent parasitism (Welbergen and Davies 2009). This leads to huge costs for the cuckoos (Davies and Brooke 1988; Welbergen and Davies 2008), and may even result in the death of the cuckoos (Molnár 1944). Hosts’ nest defenses against cuckoos prevent cuckoo parasitism (Welbergen and Davies 2009), but such defense behaviors can be passed on to other individuals through learning, strengthening anti-parasitism of the population

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