Backyard bats

Studying bats is a challenge, because we can't really see them, and we can't hear them. So I need technological assistance - this is where that previous career in software development comes in handy. To hear them, I use a device that records sound higher than we can hear, that is, ultrasound. The calls automatically trigger the detector, and they are recorded onto a simple MP3 player and later uploaded to my computer for analysis. This is a sonogram, or computer analysis, of calls that I recorded last night in a friend's back yard. I'm frankly not sure what kind of bat it was, or perhaps it was multiple bats. Most likely it's a freetail, but the signature frequency seems a bit high. I'm still a beginner at the analysis part. The bats that visited my friend's back yard were looking for dinner. It was quite cold and windy, so it's hard to believe that many bugs were out, but bat's can't exactly just stop off at the grocery store or order take-out. The calls recorded here were not social calls, but rather calls designed to bounce off any tasty bugs flying around, so that the bat could chase them, and catch them, and eat them. Yum! I recorded this using a Pettersson ultrasound recorder D240X. The visual you see is a screen capture from Sonobat software's analysis of the call. You can see the frequency of the calls along the Y axis (on the left) and time is on the X axis, along the bottom. The bat, or bats, flew along above the recorder calling out multiple times. The calls tended to start at about 50 kHz and descend to about 30, with the most power happening at about 35 kHz. Each call lasted about 8 milliseconds. Just for reference, humans can hear up to about 20 kHz, so these bats are not audible to us without some kind of detector like this.

Bats in the news

There have been some interesting recent studies on bats. First, that new bat species with the incredibly long tongue that I reported about from NASBR got an article in Nature - way to go, Nathan! Another talk that I heard at NASBR resulted in a paper in a prestigious journal. This study showed that bats change their echolocation frequency upward to avoid interference from other bat calls. Finally, some scientists discovered that big brown bats (Eptesicus fuscus) use magnetic fields to help them orient themselves. When that ability to sense the earth's magnetic fields was altered, the bats were not able to find their way home. The article doesn't say if they later found the bats and restored their magnetic super powers, but I certainly hope they did. This also got a Nature article. As for me, I'll be spending the holiday break at home, studying for the GRE and working on my thesis. We're having a real cold spell right now, so the bats are probably sleeping it off... I know that I'm really reluctant to go out there to find out.