Effective conspecific communication with aberrant calls in the common cuckoo (Cuculus canorus)

Abstract

The obligate brood parasitic common cuckoo (Cuculus canorus) is best known for its two-note “cu-coo” call, which is uttered repeatedly by adult males during the breeding season. This call advertises the male’s claim for his territory. A rare, aberrant version (“cu-kee”) was discovered in a population of cuckoos in central Hungary. In a playback experiment, we simulated conspecific territorial intrusions using either aberrant call sequences or normal calls (as control). Cuckoos responded to both calls similarly by approaching the speaker, flying around it several times, and perching on nearby trees. To identify the role of each note of these cuckoo calls, we also played sequences of the first (“cu”) or second (“coo” or “kee”) notes of the calls. Territorial males responded to first notes at similarly high frequencies as to each of the full calls, whereas responses toward either second note type were nearly absent. Thus, the first notes of both typical and aberrant cuckoo calls contain sufficient information to recognize conspecific males and the novel calls did not reduce the efficiency of male-male communication in cuckoos because the aberration occurred in the less functional second note. Significance statement Birds use songs and calls to communicate with each other, including advertising their territories to keep competitors away. However, when the acoustic signal is atypical and distorted, the receiver individual may not process it correctly. Common cuckoos recognize a territorial intruder by their well-known “cu-coo” calls. We studied a rare, aberrant version of the common cuckoo call (“cu-kee”), which differed from the normal call in the second note of the two-partite call. However, cuckoos responded similarly to both of the normal and aberrant calls in a playback experiment. When the first or second parts of the different calls were played separately, only the first part of the cuckoo calls was effective in eliciting territorial defence. Consequently, the aberrant second note did not reduce cuckoos’ communication efficiency.

Syntax errors do not disrupt acoustic communication in the common cuckoo

“…We suppose that these syntax errors are related to the extent of the signal-expression ability of cuckoos, allowing to introduce limited numbers of variations in the sequence and repeat of the elements. Accordingly, the atypical “cu-kee” form 36 can be regarded as an aberrant form of the second note (i.e., not a compositional syntax error), which we found in several individuals.…”

“…As common cuckoos utter their simple “cu-coo” calls in long series continuously, we hypothesized that the ordering of the two elements and its variants in individual calls would have less relevance than the type of the element. As a previous study 36 already revealed that the first element (“cu”) elicited similar response in receivers as the complete “cu-coo” call, we predicted that the first element (“cu”) would have more information content for male cuckoos’ acoustic communication than the “coo” element. We also predicted that the lack of this element would make the call ineffective for receivers.…”

“…Most of the trials (calls (5)–(10)) were played back in the 2021 breeding season, between May 11 and 26. Regarding the constraint in the size of the study area, the accessibility of birds, we also used trials of calls (2)–(4) played back between May 4 and 18, 2020, together with other categories not used in the present study 36 . Controls with collared dove calls were done in 2016 following the same protocols.…”

“…Male common cuckoos also did not use their 2-note advertisement call for mate attraction, and instead uttered a variant of this call (the 3-note “cu-cu-coo” 34 , 35 ) in male–female communication contexts. Additionally, an aberrant but still communicatively effective version of the basic “cu-coo” call (e.g., “cu-kee”) has also been reported in the literature 29 , 36 . However, aberrant calls differ from compositional syntax errors, as the structures within the notes are modified, which are represented by the altered shapes of their spectrograms (see e.g.…”

Testing the Interspecific Function of Female Common Cuckoo “Bubbling” Call

“…Non-passeriform vocalizations are widely assumed to be simple and stereotyped and show little variation; for example, there is a high degree of consistency in the number of syllables (Møller et al, 2016(Møller et al, , 2017 and call characteristics in individual male common cuckoo calls (Jung et al, 2014;Li et al, 2017;Zsebok et al, 2017). However, recent studies have revealed that individual male common cuckoo calls are more variable than previously thought (Deng et al, 2019a), and male common cuckoos can use these versatile vocalizations to encode different messages (Tryjanowski et al, 2018b;Xia et al, 2019;Moskat et al, 2021). Inspired by these observations, our first hypothesis is that female common cuckoos use different calls for interspecific and intraspecific communication.…”