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First published online January 30, 2009
Journal of Experimental Biology 212, 566-575 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026518

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Frequency information in the vibration-cued escape hatching of red-eyed treefrogs

Michael S. Caldwell^1,*, J. Gregory McDaniel² and Karen M. Warkentin^1,3

¹ Department of Biology, Boston University, Boston, MA 02215, USA
² Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA
³ Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Panama

^* Author for correspondence (e-mail: mpod3{at}bu.edu)

Accepted 24 November 2008

Incidental acoustic and vibrational cues generated by predators are a potential source of information for prey assessing risk. Substrate vibrations should be excited by most predators, and frequency, amplitude or temporal properties could allow prey to distinguish predator from benign-source vibrations. Red-eyed treefrog embryos detect egg predators using vibrations excited during attacks, hatching rapidly and prematurely to escape. We recorded vibrations in egg clutches during attacks by five species of predators and three common types of benign physical disturbance. We analyzed their frequency distributions to assess if and how frequency properties could be used to discriminate between vibration sources and used vibration playbacks to examine the effects of frequency properties on the escape hatching response. Vibrations produced by predators and benign disturbances generally have broad and overlapping frequency distributions, and all frequencies excited by attacks are also excited by benign disturbances. Decision rules based on the frequency distribution of vibrations alone would therefore result in either high levels of hatching in response to benign vibrations (false alarms) or common failures to hatch in response to predators (missed cues). Nevertheless, embryos hatch in response to predator and not benign disturbances in nature, and our playback results show that vibration frequency information is an important component of their hatching decision. Embryos combine frequency with temporal information to refine their hatching response. Moreover, comparing frequency spectra of predator and benign vibrations suggests that the presence of energy in frequencies outside the range characteristic of attacks might serve as an indicator of benign disturbance.

Key words: frequency, cue, decision rule, predator detection, discrimination, Agalychnis, embryo

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