Abstract
Species facing similar selection pressures should recognize heterospecific alarm signals. However, no study has so far examined heterospecific alarm-call recognition in response to parasitism by cuckoos. In this study, we tested whether two sympatric host species of the common cuckoo Cuculus canorus, Oriental reed warbler Acrocephalus orientalis (ORW, main host), and black-browed reed warbler Acrocephalus bistrigiceps (BRW, rare host), could recognize each other’s alarm calls in response to cuckoos. Dummies of common cuckoo (parasite) and Eurasian sparrowhawk Accipiter nisus (predator) were used to induce and record alarm calls of the two warbler species, respectively. In the conspecific alarm-call playback experiments, ORW responded more strongly to cuckoo alarm calls than to sparrowhawk alarm calls, while BRW responded less strongly to cuckoo alarm calls than to sparrowhawk alarm calls. In the heterospecific alarm-call playback experiments, both ORW and BRW responded less strongly to cuckoo alarm calls than sparrowhawk alarm calls. BRW seemed to learn the association between parasite-related alarm calls of the ORW and the cuckoo by observing the process of ORW attacking cuckoos. In contrast, alarm calls of BRW to cuckoos were rarely recorded in most cases. BRW with low parasite pressure still developed recognition of heterospecific parasite-related alarm call. Unintended receivers in the same community should recognize heterospecific alarm calls precisely to extract valuable information.
Highlights
Acoustic signals play an important role in animal communication systems
Yu et al (2017a) showed that even rare host great tits (Parus major) could distinguish parasites, because tits produced different alarm calls in response to Eurasian sparrowhawks Accipiter nisus and common cuckoos (Cuculus canorus)
We first examined whether regular host oriental reed warblers (Acrocephalus orientalis) and rare host black-browed reed warblers (Acrocephalus bistrigiceps) have the ability to distinguish between common cuckoos and sparrowhawks using similar methods as Yu et al (2017a), and restrict their response behavior to conspecifics alarm calls
Summary
Acoustic signals play an important role in animal communication systems. These signals can transfer diverse and meaningful information from a signaller to a receiver Yu et al (2017a) showed that even rare host great tits (Parus major) could distinguish parasites, because tits produced different alarm calls in response to Eurasian sparrowhawks Accipiter nisus and common cuckoos (Cuculus canorus). These calls caused different response behaviors to conspecific receivers. We first examined whether regular host oriental reed warblers (Acrocephalus orientalis) (hereafter ORWs) and rare host black-browed reed warblers (Acrocephalus bistrigiceps) (hereafter BRWs) have the ability to distinguish between common cuckoos and sparrowhawks using similar methods as Yu et al (2017a), and restrict their response behavior to conspecifics alarm calls. If signal recognition evolves in isolation between predator pressure and brood parasite pressure, we predicted that ORWs and BRWs would recognize and appropriately respond to alarm calls of each other to the predator, but would not recognize each others’ alarm calls to the parasite
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