Here is a video and a link to an audio recording of frog calls at the Dipper Ranch ponds on the evening of 02/20/09. Thanks to my brave nighttime companions, K. Greene and D. Bruscoe for bringing these new technologies to biological surveys on the Dipper Ranch. 'Course, I waited until after our 10 pm spaghetti dinner to show them the mountain lion-punctured deer skull I found near the Mallard Pond last year.
The video below shows a treefrog at the Plum Pond inflating his vocal sac and then his chest like a bellows to create his mating call. It also gives you an idea of the din created by many treefrogs calling at the pond. Video by K. Greene.
Notice that the Pacific treefrog advertisement calls are high, loud and nearly continuous. They repeat a double tone, krek-ek. The advertisement call is used by the males to attract females in the pond for mating. The racket sounds so loud to us, it is hard to imagine a female picking out an individual male. Obviously, treefrogs hear differently than humans do, and breed differently for that matter.
Treefrogs have other, shorter calls, some of which we occasionally hear during our surveys and I frequently hear around the farmyard and ranch during the day.
If you follow this link to Moonlittrails's Weblog, and listen carefully to the audio recording, you can hear the very low and occasional call of the California red-legged frog, chuck-chuck-chuck waaahh among all the trilling tree frogs. The last waaahh sound is not always included and is referred to as a growl or groan. Red-legged frogs will call underwater in addition to in the air. D. Brusco recorded and modified this audio clip. Fortunately, she is an excellent sound technician, and somehow edited out K. Greene and I snickering into our fists every time we heard the red-legged frog waaahh.
The first time I heard a red-legged frog call, I actually felt it before I heard it. In February 2008, I had just sat down in a disappointed huff by the Plum Pond after receiving a jubilant radio report that my fellow nighttime surveyors had heard and seen several red-legged frogs at the Mallard Pond. Although the leader of the survey team and the keen observer to have recently reported and photographed eggs of this rare frog at the Dipper ponds, at that time, I had still not seen or heard an actual red-legged frog, ever. Kinda embarrassing. I was trying to calm my anxious mind, when I thought something brushed against my jacket and made it vibrate. I was a little nervous because that night we were short one person and I was at the Plum Pond solo. I held my breathe in the darkness and then heard/felt it again. It was then that I realized I was feeling the dark vibration first through my seat chuck-chuck-chuck, and as I tuned my ear lower than the treefrog racket, I could more distinctly hear the deep sound chuck-chuck-chuck waaah. Soon my fellow surveyors joined me at the Plum Pond and we enjoyed hours of frog calls and sightings.
Now when I take new people out to listen for red-legged frogs, I encourage them to sit down and concentrate on low sounds and vibrations. I know they have finally heard it when their teeth suddenly flash in the night - undoubtable from a huge grin as they finally hear and recognize their quarry.
Ms. Bruscoe also introduced me to an article by bioacoustician Dr. Bernie Krause about bioacoustical niches. Mr. Krause believes that each vocal species, be it bird, insect, frog or jungle primate, finds its own sonic niche in pitch, pattern and timing within a geographical region. Within this acoustical territory, the individual members of a species can hear the mating, warning and other calls from each other without being covered up. Certainly, the treefrogs and red-legged frogs have very different calls even though they are occupying the same pond and breeding season. Increasingly throughout the world, human generated sounds may be occupying some of those sonic niches. Or, by altering the natural landscape, humans may be changing the mix of wildlife species at a location and thus causing formerly unassociated species to call over each other. We may be acoustically bulldozing over love songs of the night.
The CA Herps site has recordings of these two frogs and other calls and describes the correct protocol for their use by manner-minded frogs and toads. Dr. Krause's website includes animal and landscape sounds from around the world.
Pacifc treefrog, Pseudacris regilla
California red-legged frog, Rana draytonii