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.