Host alarm calls attract the unwanted attention of the brood parasitic common cuckoo

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.

Female common cuckoo calls dampen the mobbing intensity of great reed warbler hosts

“…50%; Zölei et al., 2015). Here, hosts nest in narrow reed beds running along both sides of small irrigation channels, lined with tall trees serving as vantage points for eavesdropping cuckoos (Moskát & Honza, 2000; Marton et al., 2019).…”

“…To test whether the female cuckoo's bubbling call (Moskát & Hauber, 2019) has a negative effect on host mobbing intensity, we presented 3D‐printed common cuckoo or dove models as a control to great reed warblers at their nests (following Marton et al., 2019). We performed experimental trials at great reed warbler nests ( n = 61), during the laying and early incubation stages.…”

“…These studies have now revealed that sounds emitted by brood parasites play an important role in conspecific communication (Moskát et al., 2017, 2020; Moskát & Hauber, 2019; Yu et al., 2019), and also as a means to increase the breeding success of the brood parasite. For example, a recent study demonstrated that cuckoos likely eavesdrop on the alarm calls of their hosts to locate host nests (Marton et al., 2019), while another study revealed that female cuckoos manipulate the behaviour of their hosts through their calls which are similar to those of the sparrowhawk (York & Davies, 2017). This latter study provided experimental evidence that a small host species, the reed warbler ( Acrocephalus scirpaceus , ca.…”

Female-female aggression and male responses to the two colour morphs of female common cuckoos

“…1) (see also Marton et al 2019 for a description of the decoys). Although we only had one model specimen of the grey morph, which may have resulted in visual but not acoustic pseudoreplication, this same decoy had already been used in a previous experiment where great reed warbler hosts aggressively attacked it more than controls (Marton et al 2019).…”

“…This sparrowhawk is a predator of small passerines, which includes cuckoo hosts, and this aggressive mimicry deters hosts from attacking the female cuckoo as a front-loaded antiparasitic defence strategy (Welbergen and Davies 2011). Interestingly, sparrowhawk mimicry cannot prevent cuckoos from being attacked by hosts altogether, neither in reed warblers (Acrocephalus scirpaceus) (Campobello and Sealy 2010; Welbergen and Davies 2011) nor in other passerine cuckoo hosts (Liang and Møller 2015;Moksnes et al 1991;Røskaft et al 2002a;Tryjanowski et al 2018a, b), which include larger and more aggressive Acrocephalus species (Bártol et al 2002;Dyrcz and Halupka 2006;Li et al 2015;Ma et al 2018;Marton et al 2019). Although the rufous morph of female common cuckoos is somewhat similar to common kestrels (Falco tinnunculus) (the kestrel mimicry hypothesis, Voipio 1953), an experimental study rejected the idea that the rufous plumage of female common cuckoos was an adaptation to mimic this raptor species that also preys on small passerines (Trnka et al 2015).…”