Sex-specific responses to simulated territorial intrusions in the common cuckoo: a dual function of female acoustic signaling

Abstract

The two-note call of the male common cuckoo (Cuculus canorus), the so-called "cu-coo", is well known to people as a natural and cultural signal. However, the so-called "bubbling" call of the female cuckoo is almost unknown to most, and its function in the social organization of cuckoos remains understudied. We carried out a study of a possible intraspecific communication function of female bubbling calls, using playbacks to female cuckoos in their natural environment. Regarding vocal responses, both female and male cuckoos paid attention to the bubbling calls as they consistently responded acoustically by calling but did not so during control playbacks of collared dove (Streptopelia decaocto) calls. Accordingly, in about 63% of trials, females approached the loudspeaker closely and 81% uttered bubbling calls themselves during the experiment. These results are consistent with a function that the bubbling call plays a role in territorial signaling and defense among females. Male cuckoos also showed strong responses to playbacks of bubbling calls, as they approached the speaker and themselves called in 94% of playbacks; this is consistent with a scenario that they are interested in unfamiliar, new females in the area. Specifically, males approached the speaker repeatedly by flight, often flew around it and then perched on a tree, and uttered different call types beside the general "cu-coo" (e.g., quick "cu-cu-coo", "gowk" call, and "guo" call). Our results represent an illustrative example that a simple female call may have multiple functions, as the cuckoo bubbling call advertises territory need for female cuckoos and attracts males. Significance statement Avian brood parasites lay their eggs in nests of other bird species, causing hosts to incubate, feed, and rear the parasitic offspring. Parasitic adult common cuckoos maintain a complex acoustic communication system, but female cuckoo calls are only beginning to be studied. The basic intraspecific functions of females' sparrowhawk-like "bubbling calls" have not yet been characterized, whereas interspecifically, they use it for reducing antiparasitic attacks by their hosts. Our playback experiments with bubbling calls revealed that both female and male cuckoos responded acoustically to unfamiliar bubbling calls and more males than females approached the speaker, relative to control playbacks. We conclude that bubbling call has dual basic intraspecific functions: mate attraction, and territorial spacing.

The function of three main call types in common cuckoo

“…For females, the "bubbling" call may function as a signal to defend resources, for example, host nests. Male cuckoos showing strong responses to playbacks of female "bubbling" call have also been discovered in a recent research (Moskát & Hauber, 2019). Based on these findings, and those of our previous research, which found that vocal activity of female common cuckoos in the same study population peaked in the morning , we suggest that the primary function of the female "bubbling" call in this population is intraspecific communication, rather than distraction of nest hosts.…”

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

“…The female cuckoo's bubbling call seems to be a multifunctional signal, being important in interspecific cuckoo–host relationships, as well as in conspecific communication (Deng et al, 2019; Moskát & Hauber, 2019). The bubbling call might play a role in the context of mate attraction (Moskát & Hauber, 2019; Xia et al., 2019) and could also function as a territorial signal for other conspecific females (Davies, 2015; Moskát et al., 2020). A previous study (York & Davies, 2017) tested an interspecific function of female cuckoo calls against a small host, the reed warbler, while our results revealed that this call also effectively dampened the mobbing responses of a large host, the great reed warbler.…”

“…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.…”

“…2‐s‐long bubbling calls (three calls within 30 s), and this section was repeated two times with 15‐s inter‐section silent periods. A similar structure was also used for the 2‐min dove control files (see more details of the playback in Moskát & Hauber, 2019; Moskát et al., 2020). To reduce pseudoreplication, we used three different rufous cuckoo and three dove decoys, and six different bubbling call and six dove call recordings chosen randomly.…”

“…While the adaptive similarity in appearance between the adult cuckoo and the sparrowhawk ( Accipiter nisus ) was one of the foci of the past two decades of research on brood parasites and their hosts (Davies, 2015; Trnka et al., 2012; Welbergen & Davies, 2011), the acoustic components of this similarity were only recently examined. 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).…”