Elsevier

Animal Behaviour

Volume 103, May 2015, Pages 35-44
Animal Behaviour

Repetition rate of calls used in multiple contexts communicates presence of predators to nestlings and adult birds

https://doi.org/10.1016/j.anbehav.2015.02.009Get rights and content

Highlights

  • Songbirds use the same calls in multiple contexts with different receivers.

  • Repetition rate (calls/time) varies across contexts characteristically.

  • Calls are repeated more quickly during widely relevant predator encounters.

  • Both adults and nestlings respond more strongly to quickly repeated calls.

  • Contextual call variation is a cue to receivers about the relevance of calls.

In multispecies communities, animals may come to recognize the signals of other species both by responding to common signal features and by learning about associations between signals and relevant threats. However, some signals are produced in multiple contexts. To a given receiver, such a signal may only sometimes be relevant. Here, I demonstrate that receivers use contextual variation in signal form as a cue to their relevance. Individuals from 15 species of songbirds repeated their calls rapidly when confronting widely threatening predators, but repeated the same calls more slowly during other types of social interactions. In playback experiments, repetition rate was a cue to nestling Ficedula flycatchers, which reduced their activity in response to quickly but not slowly repeated calls, and also to adult birds from a variety of species, which responded more strongly to the calls of their own and other species produced at faster rates. These results show that repetition rate is an innate or early learned contextual cue and, in combination with learning about heterospecific signals, allows receivers to fine-tune their responses to the calls of their own and other species according to their relevance, suggesting that simple rules facilitate widespread heterospecific communication networks.

Section snippets

Call Recordings

During the breeding seasons from 2007 to 2014, I located nests of small songbirds at three field sites in close proximity in the Indian Himalayas (Manali Wildlife Sanctuary: 32°14′N, 77°9′E, between 3100 and 3600 m; 2007, 2008, 2010; Mooling Forest near Keylong: 32°30′N, 76°58′E, 3400–3600 m; 2009, 2010; Jagatsukh Forest: 32°11′N, 77°12′E, 2200–2500 m; 2011), Mt Fuji in Japan (35° 22′N, 138° 45′E, 2000–2200 m; 2011) and on the Swedish island of Öland (57°10′N, 16°56′E, at sea level; 2013, 2014). In

Calls Produced in Predator and Nonpredator Contexts

Birds from each species produced calls that were highly similar in both predator and nonpredator contexts (Fig. 1, Appendix Table A1). For each acoustic measurement, only a small fraction of the variance in calls was explained by differences across contexts (call length: 5.8%; ANOVA: F1,28 = 0.058, P = 0.81; high frequency: 2.9%; F1,28 = 0.097, P = 0.77; low frequency: 3.9%; F1,28 = 0.097, P = 0.54). Within-species mean values for each measurement were similar (reconstructed ancestor node value for

Discussion

Songbirds from seven families produced acoustically similar calls both when confronting predators and during other types of social interactions. However, the same species repeated the calls at faster rates during predator interactions than in nonpredator contexts. I suggest that birds use the same, variable use calls in multiple contexts, because they have similar functions in alerting surrounding birds, whether conspecifics, heterospecifics or predators themselves. I argue that, while

Acknowledgments

I thank T. Price for contributing ideas, advice and assistance while designing, conducting and analysing experiments and while writing the manuscript and A. Qvarnström for help conducting the experiments in Sweden. I thank T. Suzuki, T. Haff, and three anonymous referees for valuable comments and suggestions on the manuscript. This work was supported by a Frank M. Chapman Memorial Fund (www.amnh.org), an NSF EAPSI Fellowship (www.nsf.gov), and an NSF Postdoctoral Fellowship in Biology (//www.nsf.gov

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