Male common cuckoos use a three-note variant of their "cu-coo" call for duetting with conspecific females.

Duetting is a coordinated form of acoustic communication with participants uttering calls or songs simultaneously and/or sequentially. Duetting is often observed in pair-bonded species, with mated females and males both contributing to the communal vocal output. We observed duetting between the sexes in the common cuckoo (Cuculus canorus), an obligate brood parasitic species without known pair formation. Specifically, female cuckoos use their sex-specific bubbling calls for duetting, while male cuckoos use a 3-note variant ("cu-cu-coo") of their typical and well-known 2-note ("cu-coo") territorial advertisement calls. The maximum frequency of the elements in the male's 3-note variants was higher relative to the 2-note calls, while durations of both the elements and the inter-element intervals were shorter. The vast majority (95 %) of the 3-note calling was detected together with the bubbling call, implying an intersexual duetting function, with the female calls preceding these male calls in 67 % of cases. The two call types in duetting followed each other rapidly (mean response time of females was 1.30 ± 0.71 SD s, and 0.76 ± 0.53 SD s in males), and typically overlapped with each other (95 %). Frequently (90 %), the male call was repeated 2-3 times, whereas the female call was repeated less frequently (9%). Our results are consistent with a main function of duetting in intersexual communication and coordination between female and male cuckoos

Syntax errors do not disrupt acoustic communication in the common cuckoo

When acoustic communication signals are distorted, receivers may misunderstand the signal, rendering it ineffective. Common cuckoos (Cuculus canorus) are popularly known for the males’ simple, two-note advertisement calls, the “cu-coo” used for declaring the male’s breeding territories. Cuckoos do not learn their calls (vocal non-learners), so they are expected to have a limited ability to produce different acoustic signals. Nevertheless, male cuckoos appear to make syntax errors (e.g., repeated, reversed, or fragmented elements) even in their simple advertisement calls. We conducted a playback experiment with male cuckoos, broadcasting ten call types, including seven modified calls with errors (e.g. “cu-cu”, and “coo-cu”) and three natural calls used for comparisons (“cu-coo”, “cu-cu-coo”, and interspecific control). Male cuckoos responded in a manner suggesting that the presence of the first (“cu”) note of the natural 2-note “cu-coo” call in any form or combination yield effective signals. However, through the elevated frequency (by about 200 Hz) and greater speed of the “cu” note, the natural 3-note version “cu-cu-coo” call appears to have gained a novel communicative function in signalling with female cuckoos. Thus, syntax errors in calls with the “cu” element are not responsible for changing the function of the male cuckoos’ “cu-coo” call

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

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

Naïve hosts of avian brood parasites accept foreign eggs, whereas older hosts fine-tune foreign egg discrimination during laying

BACKGROUND: Many potential hosts of social parasites recognize and reject foreign intruders, and reduce or altogether escape the negative impacts of parasitism. The ontogenetic basis of whether and how avian hosts recognize their own and the brood parasitic eggs remains unclear. By repeatedly parasitizing the same hosts with a consistent parasitic egg type, and contrasting the responses of naïve and older breeders, we studied ontogenetic plasticity in the rejection of foreign eggs by the great reed warbler (Acrocephalus arundinaceus), a host species of the common cuckoo (Cuculus canorus). RESULTS: In response to experimental parasitism before the onset of laying, first time breeding hosts showed almost no egg ejection, compared to higher rates of ejection in older breeders. Young birds continued to accept foreign eggs when they were subjected to repeated parasitism, whereas older birds showed even higher ejection rates later in the same laying cycle. CONCLUSIONS: Our results are consistent with the hypotheses that (i) naïve hosts need to see and learn the appearance of their own eggs to discriminate and reject foreign eggs, whereas (ii) experienced breeders possess a recognition template of their own eggs and reject parasitic eggs even without having to see their own eggs. However, we cannot exclude the possibility that other external cues and internal processes, accumulated simply with increasing age, may also modify age-specific patterns in egg rejection (e.g. more sightings of the cuckoo by older breeders). Future research should specifically track the potential role of learning in responses of individual hosts between first and subsequent breeding attempts by testing whether imprinting on a parasitized clutch reduces the rates of rejecting foreign eggs in subsequent parasitized clutches

Why should Common Cuckoos Cuculus canorus lay their eggs in host nests?

Capsule Brood parasitic Common Cuckoo Cuculus canorus chicks hatch earlier than the nestlings of their Great Reed Warbler Acrocephalus arundinaceus hosts, but hatching priority is less certain when cuckoo eggs are laid after the onset of host incubation. Aim To reveal by field observations what the optimal stage is for cuckoos to lay their eggs in relation to the host laying cycle to ensure prior hatching of the parasitic chicks. Methods We monitored the hatching of cuckoo chicks in relation to the hosts’ laying stage at which the cuckoo eggs appeared and also monitored host incubation behaviour. Results Great Reed Warblers incubated more on day 5 after the host's onset of laying relative to day 3. All cuckoo eggs hatched earlier than hosts when they were laid prior to the onset of host incubation (day 4). Cuckoo eggs also maintained hatching priority in about 2/3 of the nests when laid on days 5-6. Conclusions Most cuckoo eggs are laid prior to the onset of host incubation, and this, together with other adaptive mechanisms, ensures the prior hatching of cuckoo eggs. Cuckoo eggs laid after incubation lose the advantage of prior hatching in clutch in ca. 30% of nests

Adaptáció, koevolúció és stabilitás a gazda-költésparazita kapcsolatokban = Adaptation, coevolution and stability in host-brood parasite relationships

A madarak költésparazitizmusa a gazdafaj és a költésparazita közötti koevolúció példái. A közismert kakukk (Cuculus canorus) Magyarországon szokatlanul nagymértékben (41-68%) parazitálja a nádirigót (Acrocephalus arundinaceus), lecsökkentve annak reprodukciós sikerét. A jelen OTKA pályázatban a két faj koevolúciós adaptációit kutattuk, így pl. a gazda tojásdiszkriminációs viselkedését (tojáseltemetés, tojáskidobás és fészekelhagyás). Kimutattuk, hogy a nádirigó fejlett tojásfelismeréssel rendelkezik, s a tojások alapszíne és nem a foltozottság játszik elsődleges szerepet az idegen tojások felsimerésében. Ugyancsak kimutattuk és egy modellel érzékeltettük, hogy a gazdák felismerik saját tojásaikat és memória-sablonnal rendelkeznek róla, s ennek szűk tartományában fogadnak el mimikris kakukktojásokat. A fészekaljon belüli tojások foltozottságnak viszont együttesen van szerepe, azok kis változatossága elősegíti az idegen tojás felismerését, míg azok nagy változatossága gyengíti. Többszörös parazitizmusban a nádirigók kisebb mértékben tudják elutasítani a kakukktojásokat, s így nagyobb lesz a költésparazita reprodukciós sikere. Többek között vizsgáltuk még a kakukkfióka kihordási ösztönének az okát, azaz a tojásból kikelő fióka minden tojást és fiókát kidob a fészekből 3 napon belül. Kísérleteink szerint ennek oka, hogy jobban ki tudja sajátítani a forrásokat ha egyedül van a fészekben, s a gazdákat nagyobb méretű táplálék gyűjtésére ösztönzi. | Cases of avian brood parasitism are examples for coevolution between hosts and brood parasites. In Hungary, the well-known common cuckoos (Cuculus canorus) parasitize great reed warblers (Acrocephalus arundinaceus) at an unusually high rate (41-68%), reducing their reproductive success. We studied coevolutionary adaptations between hosts and brood parasites within the framework of the present OTKA grant, e.g. egg discrimination ability of hosts (egg burial, egg ejection and nest desertion). We showed the well-developed egg discrimination ability of great reed warblers, and the importance of background colour of eggs in respect to spottedness in egg recognition. We also revealed and showed by a model that hosts know their own eggs and have a memory-template of these eggs. They accept mimetic cuckoo eggs if their characteristics fall below the acceptance threshold. We showed that intraclucth variation of eggshell spottedness facilitates foreign egg recognition if intraclucth variation is low, but it was found an opposite effect if it was high. In multiple parasitism hosts showed high tolerance toward cuckoo eggs, resulted in a higher fledging success of the brood parasite. We also revealed that the cuckoo chicks grow up alone in host nests to utilize parental provisioning ability of hosts better than in mixed broods of hosts and cuckoos