Our friends the bats are really active today. Normally, they make a bit of noise when they see me walk by the bat house in the backyard, but today, lots of screeching. (High-pitch squeaks that sound a lot like insects — see the audio/video post below).
Archive for May, 2009
It started raining hard here last night, just around sunset. You can see the temperature drop during the rain, and then level off again afterward. Notice the peak in calls when the bats first emerge. Usually it is around 8:00 PM, just when it’s starting to get dark. But, and I’m presuming this is because of the rain, the big peak in calls signifying leaving the bat house is delayed until about 10:00 PM, after the rain lets up.
This coincides with what I heard in listening for the counter that tracks bats emerging from, or entering into the bat house. No counts until about 10, but then almost 200 transitions during the rest of the evening. It seems the bats got a late start because of the rain, but made up for it with a really active night later. Rain probably means more insects for food, too.
In future posts I’ll talk about how I count the bats entering and leaving the bat house, and show some data about how this indicator of activity changes over time.
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.
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.
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.
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.