title: A host-race of the cuckoo Cuculus canorus with nestlings attuned to the parental alarm calls of the host species.
abstract: The common cuckoo has several host-specific races, each with a distinctive egg that tends to match its host's eggs. Here, we show that the host-race specializing on reed warblers also has a host-specific nestling adaptation. In playback experiments, the nestling cuckoos responded specifically to the reed warbler's distinctive 'churr' alarm (given when a predator is near the nest), by reducing begging calls (likely to betray their location) and by displaying their orange-red gape (a preparation for defence). When reed warbler-cuckoos were cross-fostered and raised by two other regular cuckoo hosts (robins or dunnocks), they did not respond to the different alarms of these new foster-parents. Instead, they retained a specific response to reed warbler alarms but, remarkably, increased both calling and gaping. This suggests innate pre-tuning to reed warbler alarms, but with exposure necessary for development of the normal silent gaping response. By contrast, cuckoo chicks of another host-race specializing on redstarts showed no response to either redstart or reed warbler alarms. If host-races are restricted to female cuckoo lineages, then chick-tuning in reed warbler-cuckoos must be under maternal control. Alternatively, some host-races might be cryptic species, not revealed by the neutral genetic markers studied so far.
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. n.b.davies@zoo.cam.ac.uk
authors.forename: N B
authors.initials: NB
authors.lastname: Davies
authors.forename: J R
authors.initials: JR
authors.lastname: Madden
authors.forename: S H M
authors.initials: SH
authors.lastname: Butchart
authors.forename: J
authors.initials: J
authors.lastname: Rutila
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D005239:Fear / Q000502:physiology / Q000523:psychology; D005260:Female; D008297:Male; D020308:Songbirds; D014828:Vocalization, Animal