The vocal begging display ofGreatSpottedCuckooClamator glandariusnestlings in nests of its two main host species: genetic differences or developmental plasticity?

Abstract

The begging behaviour of nestlings is part of a communication system by which nestlings solicit food from their parents. In the case of brood parasitic species, nestlings in the nests of host species could achieve appropriate begging calls through three different mechanisms: (1) mimicking the host species' begging calls, (2) emitting a begging call that stimulates a wide range of hosts or (3) tuning the begging call in a way that optimizes food provisioning by foster parents. All three mechanisms could occur as a result of post-hatching environmental factors, or they may be innate when parasitic females specialize on particular host species. In this study we analysed the begging calls of Great Spotted Cuckoo nestlings in nests of its two main hosts, Eurasian Magpie Pica pica and Carrion Crow Corvus corone corone. We did not find support for the previously suggested mimetic call of cuckoo nestlings, as the structure of begging calls did not differ with respect to host species. In addition, the number of notes per call was the only trait of Cuckoo begging calls that differed when parasitizing different host species, but it was in the opposite direction from that of the begging calls of the nestlings of the two host species. Furthermore, cross-fostering experiments with nestlings that hatched in nests of the two host species yielded calls that did not support the possibility of genetic determination of begging calls of Cuckoos parasitizing different host species (e.g. host species of origin). Moreover, we found a significant effect of the identity of the host species in explaining variation in the number of notes per call. Therefore, our results suggest that Cuckoo nestlings are able to adjust their begging calls after hatching in nests of different host species by learning efficient begging displays.

Innate development of acoustic signals for host parent–offspring recognition in the brood‐parasitic Screaming CowbirdMolothrus rufoaxillaris

“…Although anecdotal, these observations further suggest that Screaming Cowbird nestlings acquire host-specific recognition cues in the complete absence of early social interactions with Baywing parents and nest mates. Our results are in agreement with previous studies in other non-evictor parasite species showing that begging calls of parasitic young can include both genetically fixed and plastic components (Rold an et al 2013, Tuero et al 2016. A difference between these other brood parasites and the Screaming Cowbird is that in the former, nestlings do not match the begging call structure of any particular host (Gloag & Kacelnik 2013, Rold an et al 2013.…”

“…S3). Our results are in agreement with previous studies in other non-evictor parasite species showing that begging calls of parasitic young can include both genetically fixed and plastic components (Rold an et al 2013, Tuero et al 2016. A recent study in the Brown-Headed Cowbird shows that begging calls of parasite fledglings, but not nestlings, consistently match the peak frequency of host's begging calls, suggesting that social experience may shape some vocal modifications that help parasites to procure resources after fledging (Liu et al 2016).…”

“…Such apparent refinement of vocal mimicry in older Screaming Cowbird nestlings had no detectable effects on host responsiveness to playbacks, but we cannot dismiss the possibility that it becomes more important after fledging, when exhibiting Baywing-like acoustic signals seems to be critical to elicit parental care and avoid host discrimination (De M arsico et al 2012). A difference between these other brood parasites and the Screaming Cowbird is that in the former, nestlings do not match the begging call structure of any particular host (Gloag & Kacelnik 2013, Rold an et al 2013. Nevertheless, it is worthwhile to note that we have observed Screaming Cowbird young recently fledged from Mockingbird nests being called and escorted by two or more adult Baywings from neighbouring territories (De M arsico & Reboreda 2008).…”

“…Experimental studies involving cross-fostering of parasitic nestlings to alternative hosts suggest that begging call structure is not genetically fixed but can be learned or shaped by early social experience, at least to some extent (Madden & Davies 2006, Langmore et al 2008, Rold an et al 2013). In the host-specialist Horsfield's Bronze Cuckoo Chrysococcyx basalis, newly hatched nestlings innately develop begging calls that closely match those of its primary host, the Superb Fairywren Malurus cyaneus, but they modify their begging call structure when reared in nests of the Buffrumped Thornbill Acanthiza reguloides to resemble this secondary host vocally (Langmore et al 2008).…”

“…Likewise, vocal differences among Common Cuckoo Cuculus canorus nestlings from different hosts are not innate but are presumably acquired through a 'trial and error' process that secures the profitability of begging calls (Madden & Davies 2006). Contrary to Bronze Cuckoos, Great Spotted Cuckoo Clamator glandarius and Shiny Cowbird Molothrus bonariensis nestlings do not acoustically resemble any particular host and show a similar overall begging call structure across host species, although call rate and amplitude can vary according to host-related environmental conditions (Rold an et al 2013, Tuero et al 2016. This diversity in the degree of vocal mimicry and plasticity across parasite species suggests multiple evolutionary solutions to the common problem of producing manipulative signals to exploit the host's parental behaviour.…”