I was just in Florida for the FotoFusion event at Palm Beach Photographic Centre in West Palm Beach (where I also have a couple of classes scheduled for mid-March – Finding Your Photographic Voice and Macro and Close-Up Photography). If you have been following these posts over the past year, you will know that bats have become an interesting challenge for me. I do want to be able to photograph them at night in the wild, a very big challenge considering they are small, don't make sounds we can hear, they come out at night, and they fly wherever they want!
One step has been to learn to find bats at night.
A bat detector uses specialized microphones to "hear" bats and then electronically modify the bat calls to a frequency we can hear. I got an Echo Meter Touch for the iPad from Wildlife Acoustics late this fall, but had not had a chance to use it. It is not cheap, but then this is a very specialized microphone and electronics module that is not like any other mic and preamp. But it is a really interesting technology that definitely opens up the night.
This module plugs into the iPad or the iPhone and uses free software from Wildlife Acoustics to process the bat sounds. It creates a sonogram of the bat calls, modifies the calls so you can hear them, and it will try to identify the bat from the calls.
I tried this at a couple of locations in Southern Florida while I was there. One was at a bridge where I had learned bats had used for roosting in the past and another at Loxahatchee National Wildlife Refuge. I tried the module on booth my iPhone and iPad, and it worked great on both. The iPhone is really easy to use and hold, while the iPad gives more display area to see the sonograms.
And I found bats. This was so cool! I only saw a couple, but I heard a lot more. Mostly they were Mexican free-tailed bats – TABR is an abbreviation for the genus and species scientific name for them. I also got a few of the Lasiurus genus (the software did not actually include a bat common to Southern Florida, the seminole bat, in its library of sounds but it did "identify" a couple of Lasiurus species that are not common there) and the big brown bat (EPFU is the abbreviation for it, below). The Mexican free-tails were so common that I started knowing them from the sonogram before the program did!
The numbers on the right side of these sonograms represent the frequency of the bat calls. The numbers are in 1000s of kilohertz. We can hear up to a little below 20,000 khz (kids can sometimes hear a little higher, and as we age, the highest frequency we can hear declines). The flat calls of the Mexican free-tails is typical. These are close to constant frequencies that they send out as they fly rapidly through the air (they are among the fastest of bats) and search for insects (mostly moths for this species).
The higher calls that have a curve are typical of big brown bats and many other bats (other bats are often even higher in frequency). That curve represents a frequency modulation, or changing frequency during the call, which helps these bats better discern the kind of insect in front of them. The blue "noise" below is just that, ground noise.
By the way, if you are interested in a great adventure nature book, check out Merlin Tuttle's autobiography, The Secret Lives of Bats. Tuttle has been an amazing researcher who has done more than anyone to promote bat awareness. He has also photographed most of the bats of the entire world. And he is more than a little crazy! If you think that the stories he tells are exaggerated for effect, he still has done some things in working to find and learn about bats that make him lucky to be alive. But these adventures do make for a lively book!