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Host parent responses to heterospecific parasite nestling alarm calls are independent of past and current experience with experimental brood parasitism


Communication between parents and dependent offspring is critical not only during provisioning, but also in antipredator contexts. In altricial birds, a top cause of reproductive failure is nest predation, and alarm calls both by parents and chicks can serve to alert others and increase the likelihood of offspring escaping predation. Understanding the factors that determine the strength of parental antipredator responses to different nestling alarm calls can provide insight into parent–offspring recognition. The prothonotary warbler (Protonotaria citrea), a host of the obligate brood parasite, the brown-headed cowbird (Molothrus ater), never rejects cowbird young and raises the parasite together with its own offspring. To determine whether warbler parents learn cowbird nestling alarm calls, we presented experimentally parasitized or non-parasitized parents with playbacks of conspecific warbler, parasitic cowbird, and a harmless heterospecific control, eastern bluebird (Sialis sialis), nestling alarm calls. We recorded the latency to respond and the number of chips given by members of the resident warbler pair. We found that parents were most likely to respond to warbler nestling alarm calls, least likely to respond to bluebird calls, with a statistically intermediate likelihood of responding to cowbird calls. Critically, current and past parasitism status did not affect the likelihood of response to any playback or the number of chips given, however, currently parasitized parents had greater response latencies to playbacks than non-parasitized parents. These results suggest that warbler parents do not learn cowbird alarm calls from breeding experiences and, in turn, that cowbirds may employ a generalized, bet-hedging alarm call.

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The dataset and code generated and/or analyzed during this study are publicly available in the FigShare depository at:


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We thank Mark Stanback for providing the eastern bluebird nestlings’ alarm calls, Nick Antonson for providing some of the prothonotary warbler and brown-headed cowbird nestling alarm calls, Lauryn Benedict for discussions, and Shelby Lawson for assistance in generating playback audio files. Funding for this project was provided by the University of Illinois at Urbana-Champaign School of Integrative Biology Isabel Norton Award and Odum-Kendeigh Summer Research Award. This work was also supported in part by an Illinois Distinguished Fellowship (to HMS), the Harley Jones Van Cleave Professorship and the Center for Advanced Study at the University of Illinois (to MEH), and the Wissenschaftskolleg zu Berlin (to MEH).

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Correspondence to H. M. Scharf.

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Scharf, H.M., Schelsky, W.M., Chamberlain, M.L. et al. Host parent responses to heterospecific parasite nestling alarm calls are independent of past and current experience with experimental brood parasitism. Anim Cogn 25, 1289–1298 (2022).

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  • Recognition
  • Communication
  • Distress call
  • Predation
  • Brood parasitism