Abstract
Female common cuckoo (Cuculus canorous) predator-like “bubbling” calls distract host parental attention and reduce the egg rejection rate. Such “bubbling” calls are also frequently used to attract males and deter territorial rivals in intraspecies contact, and these calls are an ancestral character in many cuckoo species. Although hosts have had sufficient time to become familiar with this call and evolve anti-parasitic strategies, why are the hosts fooled by this “bubbling” call? We propose two hypotheses. The first hypothesis proposes that call variation reduces the opportunity for host species to correctly assess cuckoo tricks. In contrast, the second hypothesis proposes that the cost of behavior may prevent the antiparasitic strategy from evolving. In the study, we tested the prerequisites of these hypotheses, by investigating whether cuckoo calls vary during the day and testing whether the predator-like calls suppress bird activities. Based on field recordings from three different areas, we found high overlap in the calls generated during different periods. Oriental great reed warblers (Acrocephalus orientalis), a host species, did not show different responses toward the playback of female common cuckoo calls generated before noon or afternoon. Based on bird count data, we found that predator-like call playback is insufficient for suppressing bird activities. Therefore, none of the prerequisites were supported by our field data. We discuss the potential reasons for our findings and hope to inspire more research examining female cuckoo vocalizations.
Highlights
The arms race between the common cuckoo (Cuculus canorous) and its hosts is a classic example of coevolution (Poulin and Forbes, 2012; Moksnes et al, 2013)
After confirming that there was no temporal effect, Fisher’s exact test was used to compare the frequency of “response” among the four playback sounds
Calls generated before noon were longer in duration (ANOVA: F1,311 = 8.10, p = 0.005) than calls generated after noon, and there was no significant difference in other variables between different periods: maximum frequency (ANOVA: F1,311 = 3.68, p = 0.056), minimum frequency (ANOVA: F1,311 = 0.09, p = 0.763), and number of notes (ANOVA: F1,311 = 1.87, p = 0.173)
Summary
The arms race between the common cuckoo (Cuculus canorous) and its hosts is a classic example of coevolution (Poulin and Forbes, 2012; Moksnes et al, 2013). The “bubbling” call of female common cuckoos is considered a parasitic strategy to mimic hawks This predatorlike call diverts the attention of reed warbler (Acrocephalus scirpaceus) parents and reduces the egg rejection rate (York and Davies, 2017). York and Davies (2017) found blue tits (Cyanistes caeruleus) and great tits (Parus major) increased their vigilance after hearing female “bubbling” calls, similar to how they respond to sparrowhawk (Accipiter nisus) calls; Jiang et al (2021) found that both female common cuckoo and sparrowhawk calls elicited vigilance and escape responses from chickens (Gallus gallus domesticus). As there are clear differences between female common cuckoo “bubbling” calls and sparrowhawk calls, why are the hosts fooled by this “bubbling” call?
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