I have lots of recordings of the Spotted Chorus Frog (Pseudacris clarkii) since it is one of the more common anuran species in south-central Texas where I live. However, I began to wonder about the transmission of its call in the water rather than in the air. How much of what female frogs "hear" is being transferred through the water?
So I found a spot in Dimmitt County, Texas in June of 2013 where a group of Spotted Chorus Frogs were calling.
Here's what they sounded like:
Here is a comparison of the above water recording and the underwater recording. The first 10 seconds are above water and the last 10 seconds are below water.
When you compare the spectrograms for the two recordings, you can see that the dominant frequency of the call above water is somewhere around 3 Khz although there are frequencies in the call above and below that frequency. The call is heard up as high as almost 7 Khz and there is a strong band of sound in the 1-2 Khz range.
Underwater, that higher frequency part of the call is lost and the dominant frequency is the lower part of the call in the 1-2 Khz frequency band and the higher frequencies, which are so dominant in the air, are almost lost.
This explains, in part, that species with deeper, low frequency calls like the Ranid frogs tend to call from in the water while frogs that call out of the water (Chirping Frogs Eleutherodactylus) tend to have higher pitched calls. The higher pitched calls would not be as effective in drawing the attention of females that were in the water. Some species of Ranid frogs even call from underwater (e.g. Rana aurora calling underwater).
© Chris Harrison 2013
* a hydrophone is an underwater microphone. Mine was made simply by putting the finger of a latex glove over the end of an inexpensive lavalier (lapel) microphone from Radio Shack (~$30) and sealing the finger of the glove with cable ties and silicone sealant.