Seasonal and diurnal patterns of population vocal activity in avian brood parasites

Abstract

Patterns of vocal activity may involve information about vocalizations themselves as well as their function. In birds, vocal activity at the individual and population level is generally closely associated with breeding cycles, reaching the peak during territorial and mating competition, and decreasing with the onset of egg incubation and chick feeding. However, little is known about patterns of vocal activity in avian brood parasites that have unusual breeding cycles without parental care. Using passive acoustic monitoring, we determined the seasonal and diurnal patterns of population vocal activity in two avian brood parasites: the Common Cuckoo Cuculus canorus and the Lesser Cuckoo C. poliocephalus. We found that both species and both sexes showed a similarly highly structured pattern of seasonal vocal activity, reaching a sharp peak in the early breeding season when birds compete for territories and mates, although males sang more frequently than females. Likewise, the diurnal patterns of vocal activity were similar in both species and both sexes of cuckoos, with peak activity occurring around dawn. Nocturnal calls by male cuckoos were also detected in both species, but only in the early breeding season. Collectively, the observed patterns of population vocal activity may suggest that the absence of parental care may not extend the period of vocal activity in these two species of brood parasites.

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

“…Recent research has shown that acoustic signals are involved in the arms race between common cuckoos and their hosts (York and Davies, 2017;Jiang et al, 2021;Marton et al, 2021). Female common cuckoos frequently use "bubbling" calls for both interspecific and intraspecific functions during the breeding season (Deng et al, 2019b;Moskat and Hauber, 2019;Yoo et al, 2020). The starting point of our study is the question: Why are the hosts fooled by this "bubbling" call?…”

“…Recently, the "bubbling" call of female common cuckoos has been included in the long list of cuckoo tricks after the pioneering work by York and Davies (2017). This "bubbling" call type is frequently used when female common cuckoos fly or perch on branches (Deng et al, 2019b;Moskat and Hauber, 2019), and it is an ancestral character in many cuckoo species (Kim et al, 2017;Yoo et al, 2020). Thus, hosts have had sufficient opportunities to become familiar with this call and to evolve anti-parasitic strategies.…”

“…One possible reason is that the hosts have not had sufficient time to evolve the ability to distinguish female common cuckoo calls from predator calls. However, this explanation is unlikely, given that predator-like female calls are a common trait in at least four cuckoo species (Kim et al, 2017;Yoo et al, 2020), indicating that they are not recently evolved strategies. Another possibility is that hosts have not had sufficient opportunities to become familiar with female common cuckoo calls and distinguish them from predator calls.…”

“…This hypothesis would be supported if female common cuckoos rarely use this predator-like call (e.g., using this call after parasitizing a host's clutch) (York and Davies, 2017). However, female common cuckoos also use "bubbling" calls to attract males and deter territorial rivals when they fly or perch on branches (Deng et al, 2019b;Moskat and Hauber, 2019;Yoo et al, 2020). More than 90% of all calls occur during the morning rather than during the egg laying time in the afternoon (Gong et al, 2020).…”

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

“…Common cuckoos (Cuculus canorus) are obligate avian brood parasites that lay their eggs in the nests of other bird species, and leave the incubation and rearing of their progeny to these hosts (Payne 2005;Erritzøe et al 2012). Common cuckoos have a simple acoustic repertoire (Lei et al 2005); their most famous advertisement call ("cu-coo") is frequently emitted during the breeding season (Deng et al 2019a;Yoo et al 2020). Sometimes, this characteristic call has unique or aberrant features (Møller et al 2016), and individual cuckoos can be identified based on their call variation; for example, an individual cuckoo was tracked in Germany by its unusual calls for several years (Naumann 1901).…”