A "chick-a-dee" or a "co-qui"?

I read with great interest the Report “Allometry of alarm calls: black-capped chickadees encode information about predator size” by C. N. Templeton et al. (24 June, p. [1934][1]), who show that black-capped chickadees utilize a graded-response alarm call to warn against predators with differences in risk as measured by predator size. I was struck by the similarity between the findings of this work and the graded-response aggressive calls of Eleutherodactylus frogs. Similar to the chickadees'” chick-a-dee” calls, where increasing repetition of the “dee” note denotes increased threat, the two-note “co-qui” call of the Puerto Rican coqui, Eleutherodactylus coqui , is used with increasing repetition of the second “qui” note during increasingly aggressive interactions with conspecific nest predators ([1][2]). Other Eleutherodactylus species also use a similar aggressive call system when confronted with conspecific or other predators ([2][3], [3][4]). A possible difference between these signaling systems may be in the interpretation of the calls by the receiver (in the case of the chickadees, this would include other birds at risk of predation, and in the case of the coquis, this would include the predator itself). In either case, this type of sophisticated, graded-response acoustic communication that implies knowledge of the level of threat posed by a predator and conveys this information to a receiver is not limited to birds and mammals, but is also used by lower vertebrates. ![Figure][5] An Eleutherodactylus frog and a black-capped chickadee. CREDITS: RAFAEL I. MARQUEZ/CALPHOTOS; DONNA DEWHURST/USFWS 1. 1.[↵][6] 1. M. M. Stewart, 2. S. A. Rand , Copeia 1991, 1013 (1991). [OpenUrl][7][CrossRef][8] 2. 2.[↵][9] 1. K. E. Ovaska, 2. J. Caldbeck , Anim. Behav. 54, 181 (1997). [OpenUrl][10][CrossRef][11][PubMed][12][Web of Science][13] 3. 3.[↵][14] 1. S. F. Michael , J. Herpetol. 31, 453 (1997). [OpenUrl][15] # A "Chick-a-dee" or a "Co-qui"? {#article-title-2} We thank Michael for pointing out graded alarm signaling by some Eleutherodactylus frogs. We suspect that many other species, from a wide variety of taxonomic groups, may employ similar graded signaling systems. However, one exciting aspect of the chickadee alarm call communication system is that it incorporates not only a graded signaling system, where subtle variations in the “chick-a-dee” call reflect the degree of threat a perched predator represents, but also aspects of a functionally referential signaling system, where different types of vocalizations, “chick-a-dee” or “seet,” refer to the type of predator encounter. Careful examination of other species that are faced with challenging selection pressures from multiple predators may even reveal more complex communication systems. [1]: /lookup/doi/10.1126/science.1108841 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: pending:yes [6]: #xref-ref-1-1 "View reference 1. in text" [7]: {openurl}?query=rft.jtitle%253DCopeia%26rft.volume%253D1991%26rft.spage%253D1013%26rft.atitle%253DCOPEIA%26rft_id%253Dinfo%253Adoi%252F10.2307%252F1446096%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [8]: /lookup/external-ref?access_num=10.2307/1446096&link_type=DOI [9]: #xref-ref-2-1 "View reference 2. in text" [10]: {openurl}?query=rft.jtitle%253DAnimal%2BBehaviour%26rft.stitle%253DAnimal%2BBehaviour%26rft.aulast%253DOvaska%26rft.auinit1%253DK.%2BE.%26rft.volume%253D54%26rft.issue%253D1%26rft.spage%253D181%26rft.epage%253D188%26rft.atitle%253DVocal%2Bbehaviour%2Bof%2Bthe%2Bfrog%2BEleutherodactylus%2Bantillensison%2Bthe%2BBritish%2BVirgin%2BIslands%26rft_id%253Dinfo%253Adoi%252F10.1006%252Fanbe.1996.0414%26rft_id%253Dinfo%253Apmid%252F9268448%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [11]: /lookup/external-ref?access_num=10.1006/anbe.1996.0414&link_type=DOI [12]: /lookup/external-ref?access_num=9268448&link_type=MED&atom=%2Fsci%2F310%2F5748%2F620.2.atom [13]: /lookup/external-ref?access_num=A1997XM49800019&link_type=ISI [14]: #xref-ref-3-1 "View reference 3. in text" [15]: {openurl}?query=rft.jtitle%253DJ.%2BHerpetol.%26rft.volume%253D31%26rft.spage%253D453%26rft.atitle%253DJ%2BHERPETOL%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx