Daytime

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).

In fact, one individual actually came out a bit onto the landing area to screech at me. I snapped a couple pictures with my digital camera, but I had to crop and enhance them a lot since the bat and the bat house are silhouetted against a very bright sky, and the bat is very dark against the brown-painted landing area.

The image above is a heavily contrast-enhanced version of the image. I was standing on a short step ladder, about six feet from the bat house.

Here's a shot cropped to show just the bat house opening, but only enhanced slightly so that you can see the true colors. No wonder bats are so hard to see at night -- they're flying fast, they're pretty much silent (to us) and they're dark brown or black.

Why so much activity? I have several theories, none of them really tested (or testable).

First, we've had a lot of rain. Over the past ten days, I measured about 13 inches of rain. This could have a couple of implications for the bats. For one thing, there were many nights were it was tough to even get out of the bat house for the driving rain, and I suspect that hunting for insects is more complex when it's raining hard. (Notice how much later the bats emerge on the rainy nights graphed in the posts below. ) For another, the insect population is now booming with mosquitoes and other insects very prevalent at my house. This means more food after a possibly hungry, rainy interval. Maybe this has got the bats more worked up?

Second, perhaps they have pups? I don't know the mating habits of bats, but I'd suspect that they may have young now. If so, then maybe the individual peeking out so aggressively (well, for a normally very shy species, anyway) has the role of sentry or guard?

Time to count some bats at the evening emergence soon.

Rain

Here's a rain effect on bat emergence. Compare this graph with the one from 5/16, posted below.

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.

Echos

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

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

NIR_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?

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.

Welcome

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.