As Spring nears It's time to consider brushing up on your frog calls, either for personal fun or so that you can help with amphibian surveys. There's nothing like being able to pick out specific species of frogs by their calls. It's like learning the notes of music. Now I'll admit that I'm rusty, every year Spring rolls around and I find myself dragging out the ear buds and MP3 and practicing. I usually get a whole bunch wrong, but it's fun relearning.
Let's refresh on the basics. Most often it's only the male frogs call, and calls are species specific though there are dialects by region (croak, croak, croak yall). Dialects allow males to self-sort and avoid competing with males from other areas that are far away or outside their region. Male frogs call to attract mates and to advertise their fitness to females. Mostly mating is done at night under cover of darkness so frogs use vocalizations instead of visual displays. Calls are produced in the larynx and are amplified by one or more vocal sacs. These sacs are thin membranes of skin that are either directly under the chin or extending from chin to mouth. Female frogs may respond to the males to encourage their advances with short croaks or other sounds (some females object quite vocally if they don't find the male's advances desired).
When many frogs call at once it's called a "chorus." Choruses can be quite loud, and the pitch and loudness may increase if there is heavy traffic or noise nearby. Male frogs conserve energy when rivals are not near-by and they have "low energy" calls that simply establish their territory. When competition is high they expend more energy to call more loudly, but what is unique is that they call in a species specific pattern with the other males. This allows all males to be heard without being completely drowned out. This type of cooperation is a unique strategy in the animal kingdom shared by vocal insects and frogs (for those with a mad pash. for reading scientific papers check out this doozy on the call-timing algorithm of the white-lipped frog). There are probably multiple reasons for this strategy but most likely it has to do with increasing fitness by decreasing energy expended calling, because everyone gets a chance.
Now let's get on to the resources you need to brush up or even learn frog calls for the first time. There are a few things you might find useful before you start.
First, invest in a nice pair of ear buds or head phones. For those with pets this is especially critical. I've had cats come flying in from all parts of the house because they hear my birds or frogs chirping away while I'm trying to learn the calls (it's distracting when they're climbing around on the stereo stalking like mighty jungle cats and swatting at the speakers). I find metro riders are also less than enthusiastic with frog calls too.
Next, decide how you're going to learn. I have MP3s downloaded on my phone and computer and I also learn by taking online quizzes. If you're not so tech savvy then consider a CD player and books. I'll provide links for all of these resources below.
There are only two or three good low-tech resources out there to learn frog calls but they are tried and true. I've included links to where you find them on Amazon.
There are quite a few field guides out there that can help you learn to identify frogs by sight, and even a great coloring book for learning reptiles and amphibians. Here are a few of the best options:
Citizen Science for Amphibian Monitoring
There are also many local organizations in each state that collect reptile and amphibian data. In my state, Maryland, we have the Maryland Reptile and Amphibian Atlas, which is run by the Department of Natural Resources. Google your state and see what you can find.
Now that you have the resources it's time to put those ear buds in, begin reviewing your frog calls while it's still cold and snowy, and get ready to get out there when the weather turns warmer. Please consider volunteering some time to the organizations listed above. Some only ask for 3 minutes a night twice a week! You can help contribute with your new-found skills.
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