An Introduction to My Wood Frog Vocalization Experiment
by, October 9th, 2011 at 01:58 PM (1742 Views)
Quawk quawk! Every May to April here in Fairbanks, Alaska you can hear the melodic sounds of the vocalizing male Wood frogs (Rana sylvatica). It’s one of the sure signs that spring is here and that summer is upon us. Despite the fact that it’s cold outside and snow may still be on the ground, it’s the frogs’ breeding season and anywhere from a week to three weeks you can hear the duck like calls of these secretive frogs. And then you almost never hear them calling again until next spring. Why do these frogs rarely call outside of the breeding season or if they do on occasion, what’s the reason? The cause is not entirely known and I am interested in finding out.
My curiosity was aroused on this topic a few years back, when I first captured four Wood frogs: 2 adult females, 1 adult male, and 1 juvenile. My primary goal in collecting these frogs was to note and observe their feeding behavior. However, that soon changed when my juvenile matured into a male, and thus started to croak. I was confused as to why the little guy started to vocalize….Was he unsure about the noises he heard, i.e. the vacuum, radio, or TV, thinking they were other frogs? Was he practicing his chorus for the mating season? Were the barometric pressure, temperature, and humidity levels optimum for vocalizing? I literally had no idea and wanted to find an answer. I was unable to design an experiment at the time, but through persistence, patience, and careful planning, I was able to acquire a permit to carry out an experiment involving six wood frogs.
The objective of this experiment is to stimulate vocalizations in captive male Wood frogs in response to previously recorded choruses. Furthermore, I want to compare the characteristics and patterns of previously recorded Wood frog vocalizations with calls stimulated in captivity by adult male Wood frogs and juvenile male Wood frogs that had been captured prior to being exposed to a mating season. For juveniles that turn out to be females, they too will be exposed to the same recorded choruses as the males and will instead be tested for phonotaxis, or the movement of an organism in relation to a sound source.
The experiment began with the collection of approximately 5 Wood Frogs (three adults and two juveniles), that have been separated into two 10 gallon terrariums according to life stage, i.e. the adults in one tank and the juveniles in the other. Originally I designed the experiment to include 3 juveniles in addition to the 3 adult males. However, during the quarantine process, several frogs died resulting in subsequent collections. The last collection, which was made to find a juvenile, failed as it was too late in the season to find frogs: they were in the pre-hibernation stage. To reduce as much stress as possible for the frogs I have successfully captured and quarantined, the tank set ups have been designed to mimic the Wood frogs habitat. The terrarium design is as follows (Bartlett 1996): An inch layer of river rock and screening material were placed at the bottom of the tanks to serve as a filtration system for the terrestrial vegetation. Heavy items, i.e. rocks or logs, were placed on top of the river rock and set firmly in place, to prevent injuries to the frogs. Approximately, 2 inches of topsoil was added on top of the river rock. Moss, ferns, and other terrestrial plants, gathered from the site collection, were planted in the soil. The temperature in the housing tanks is being kept between 65-75 F and the humidity between 60-70%. The third terrarium (the testing tank) was set up as described above; however, the temperature and amount of light are to be varied.
After acclimating to their new surroundings for a time, the Wood frogs will then be separated from their terrariums one by one, and placed in a separate temperature and light controlled terrarium for one week, the testing tank. Here, the frogs will be exposed to either Test A conditions or Test B conditions. During Test A, each frog will be tested under conditions that resemble the Wood frog’s breeding season during late April and early May. The terrarium light will be left on for 10 hours and the temperature will be kept at 40 F-50 F. This data is the average temperature and daylight hours for Fairbanks during the Wood frogs’ mating season. During Test B, each frog will tested under normal living conditions, with the temperatures between 70 F-80 F and the light left on for approximately 15 hours. For both tests, the frogs will be exposed to a series of recorded Wood frog vocalizations. These vocalizations will be played on a stereo near the frog’s tank between 11 am and 1 pm and between 10 pm and midnight. It is important to note that Wood frog vocalization activity is most active at these times during the mating season (Klein 2009). Any changes to behavior, i.e. responding to the vocalizations or showing signs of phonotaxis (Bee 2007), will be recorded or documented. The vocalizations will be recorded on a hand held recorder and calls and notes will be subsequently be analyzed with Sound Ruler (Gridi-Papp 2002-2007). The calls recorded during the experiment will be compared with the Wood frog chorus recorded earlier this year. Once testing is complete, the frogs will be placed back into their normal living conditions.
It is also significant to note that a third test, Test C, may be added to the experimental design. Over the past 7 years of observing Wood frog behaviors, I have noticed that male Woodies tend to respond to certain notes in music. If so, instead of Wood frog vocalizations recordings that the frogs will be exposed to, the amphibians will instead be exposed to different genres of music, in particular classical music. The conditions will be set similar to Test B. If this test is unable to be carried out, it will be tested at a later time and with a future experiment.
What are my predictions on my experiment? Under Test A conditions, I predict that the male Wood frogs will either respond with calls of their own, will display phonotaxis, or both. For the juveniles, I predict that phonotaxis will be possible; however, I have doubts that they will display any sign of recognition. Under Test B conditions, I predict that the adult males will not respond with calls of their own, but instead might display phonotaxis. As for the juveniles, I believe they will display the same predictions as Test A. If needed, the experiment will be adjusted accordingly.
Bartlett, R.D. and Patricia. Frogs, Toads, and Treefrogs. New York: Barron’s, 1996.
---. Terrarium and Cage Construction and Care. New York: Barron’s, 1999
Bee, Mark A. 2007. Selective phonotaxis by male wood frogs (Rana sylvatica)
to the sound of a chorus. Behav Ecol Sociogiol 61: 955-966
Gridi-Papp, M. 2002-2007. Software Sound Ruler version 0.9.6.0. Available in:
Klein, Susan C. “Alaska Wood Frog Monitoring Project: Where are the Wood Frogs?” 2009.
Alaska Wood Frog Monitoring Project. 29 Oct. 2009
“phonotaxis.” A Dictionary of Biology. 2004 Encyclopedia.com. 31 Aug. 2010
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