Abstract
It is well known that avian brood parasites lay their eggs in the nests of other bird species, called hosts. It remains less clear, however, just how parasites are able to recognize their hosts and identify the exact location of the appropriate nests to lay their eggs in. While previous studies attributed high importance to visual signals in finding the hosts’ nests (e.g. nest building activity or the distance and direct sight of the nest from vantage points used by the brood parasites), the role of host acoustic signals during the nest searching stage has been largely neglected. We present experimental evidence that both female and male common cuckoos Cuculus canorus pay attention to their host’s, the great reed warbler’s Acrocephalus arundinaceus alarm calls, relative to the calls of an unparasitized species used as controls. Parallel to this, we found no difference between the visibility of parasitized and unparasitized nests during drone flights, but great reed warblers that alarmed more frequently experienced higher rates of parasitism. We conclude that alarm calls might be advantageous for the hosts when used against enemies or for alerting conspecifics, but can act in a detrimental manner by providing important nest location cues for eavesdropping brood parasites. Our results suggest that host alarm calls may constitute a suitable trait on which cuckoo nestlings can imprint on to recognize their primary host species later in life. Our study contributes to the growing body of knowledge regarding the context-dependency of animal signals, by providing a novel example of a beneficial acoustic trait intercepted by a heterospecific and used against the emitter.
Highlights
It is well known that avian brood parasites lay their eggs in the nests of other bird species, called hosts
We found that the nests of the great reed warbler, the host of the brood parasitic common cuckoo in our study area, are hardly visible in the dense reed bed from the nearest cuckoo perches and from mid-air
The alarm calls uttered by the hosts are likely to be good nest location cues for the brood parasites, since both female and male common cuckoos exhibited interest towards alarming hosts and alarm call playbacks
Summary
It is well known that avian brood parasites lay their eggs in the nests of other bird species, called hosts. The recognition of the gent-specific host species and the localization of potential nests is of paramount importance for the fitness of brood parasites, the mechanisms utilized to recognize primary host species and locate their nests remains incompletely understood Female cuckoos monitor their potential hosts from vantage points, from where they locate suitable nests to lay their egg in[24]. To the best of our knowledge, only one study was conducted regarding host vocalization and the nest searching strategy of common cuckoos, which found that the conspicuous and recognizable song of the male great reed warbler was not a good cue for a female cuckoo when searching for a preferred host’s nest[13]
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