May 17th, 2009

Here’s a graph of bat echolocation calls throughout the night of 5/16. The yellow line shows the total number of chirps produced as the bats navigate and hunt over my backyard and around the bat house. Since each chirp is a whole set of clicks and very short tones, a single call can produce dozens of loggings. The bat detector converts each call into a series of pulses and each pulse gets counted by a microcontroller. That accounts for the high numbers originating from a maximum of about fifty individual bats who might be in range of the bat detector.

The light blue line is temperature, uncalibrated for now. It was probably in the mid 70’s here last night.

The purple crosses are wind gusts, as counted by an anemometer located next to the detector. Maybe it is coincidence, but it does look as if bat activity picked up as the wind died down last night. Interesting.

The X axis is time, starting around 6:00 PM Saturday night, and ending around 8:00 AM this Sunday morning.

In future posts, I’ll go explain the equipment that logs these data.

Some images to start

May 17th, 2009

Here’s a link to some images I’ve taken of bats.


All are nighttime, Infra-Red shots, grabbed from video, using an Infra-Red flash. I’ll be posting more images over time, since I’m always taking pictures, and I’ll post the more interesting ones here.

Karaoke Bats?

May 16th, 2009

Ok, maybe Karaoke is stretching it. But bats do “sing”, sort of.

First, they make plenty of audible chirps and clicks and squawks during the day in the bat house. In fact, we first figured out that we had residents in our backyard bat house when my daughter heard them chirping one afternoon while she was hanging out laundry. Thinking that birds had invaded the bat house that had sat empty the preceding two years, I shined a flashlight up inside, and — Wow — not birds but bats. They’ve been there ever since.

Second, and more famously, bats use bio-sonar to echolocate. Basically they make really loud, very high-pitched sounds, listen for the return echos from objects and potential prey, and then navigate appropriately toward or away from obstacles. These chirps are normally inaudible to humans, since they begin at about 40 Kilohertz (40,000 cycles per second), roughly twice the highest frequency that we can hear. But you can assemble or purchase a simple bat detector that will translate the bat’s echolocation sounds down to the range of our ears.

Here’s an example of what they sound like:

In future posts, we’ll talk about bat detectors and how you can hear and record bats flying through your neighborhood.


May 16th, 2009

This blog is about bats — flying mammals, that is. I’ve been watching, photographing, logging, recording and otherwise “stalking” the bats in my backyard for a couple of years now, and I thought I’d share some of what I’ve seen and heard.

Posts will be of several sorts: pictures, mostly night time shots grabbed from video frames, audio recordings of bat sounds (both audible and inaudible), and data about bat activity — lots and lots of data.

I hope you will enjoy what we post here, and I hope that you’ll come to better understand and appreciate these most “mis-underestimated” of animals.