The Impact of Calling Site on Call Degradation and Female Discrimination in the Gray Treefrog
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Pace University, Biology and Health Sciences, United States
Breeding aggregations of gray treefrogs (Hyla versicolor) form during early evenings in and adjacent to wetlands. In a typical chorus, females approach calling males using phonotaxis from areas adjacent to the chorus (e.g. surrounding forest). Males vocally advertise for females from a range of calling sites: the water surface, shore edge, emergent vegetation, shrubs, saplings, and trees. The specific height, orientation and location of males on vegetation are quite variable. Males produce calls of adjustable duration which consist of trains of pulses, and females often discriminate in favor of males producing calls with more pulses in their calls. The pulse structure of the advertisement calls is especially important to call recognition and species discrimination by females yet is vulnerable to structural degradation when calls are transmitted through natural habitats. A major goal of this study was to determine the consequences of calling site choice by males for call degradation and ultimately female choice of a mate. We also examined the height of male perches in the field to assess the possibility that males choose calling sites for which their calls would be less vulnerable to degradation.
To evaluate the effects of calling site on call degradation we broadcast synthetic advertisement calls through forest, over open terrain, and across water at areas where gray treefrogs breed. The calls were recorded at distances of 1, 2, 4, 8, 16 and 32 meters. We varied speaker and microphone heights for a total of five elevation combinations (ranging from ground level to a height of 1.5 m). We quantified structural degradation in recorded calls using “Delta V”, a measure of relative sound energy in call pulses and interpulse intervals. Delta V is expected to decrease with call degradation. A subset of recorded calls was used in two-speaker discrimination tests with females. Finally, we examined male selection of perch height by recording the locations of calling males on 8-rung trellises positioned around the periphery of a breeding pond in a forest.
We found the greatest degradation for calls broadcast through forest followed by calls transmitted across open terrain and then water. At relatively small source-receiver separations, elevation had only small effects on degradation. However, for separations greater than 4-meters (especially through forest), elevation had a significant impact on Delta V - with calls broadcast and recorded near the substrate particularly vulnerable to degradation. Choice tests demonstrated that such levels of degradation could significantly reduce a male’s attractiveness. Perhaps for this reason, males only seldom called from low rungs of trellises.
Keywords:
bioacoustics,
Call Degradation,
Female Choice,
Male Behavior,
Treefrogs
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster Presentation (see alternatives below as well)
Topic:
Sensory: Audition
Citation:
Schwartz
J
(2012). The Impact of Calling Site on Call Degradation and Female Discrimination in the Gray Treefrog.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00394
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Received:
01 May 2012;
Published Online:
07 Jul 2012.
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Correspondence:
Dr. Joshua Schwartz, Pace University, Biology and Health Sciences, Pleasantville, NY, 10570, United States, jschwartz2@pace.edu