August 14th, 2010

I used to think that things around the bat house fell into a simple pattern — drop down and fly off at dusk, chase some bugs all night, and then swoop back into the bat house just before dawn. I soon found out this view of the bat life was way too simple.

This particular video shows a peak time for activity around the bat house, just before dawn. Rather than straggling in one-by-one and disappearing quickly into the bat house, these bats like to circle around, en masse for a while. Notice all the times when an individual almost disappears into the bat house, but then quickly turns and buzzes off. In a few minutes, when it gets a bit lighter everyone will eventually land and enter, and things will be quiet, except for a few squeaks and chirps.

Looking at the data from the various sensors along the bat house entrance I could see that bats were coming and going not just near dusk and dawn, but on and off during the night. A typical evening might have the bats leaving around 8:30, with everything quiet until maybe 10:30, when all of a sudden, bats swooping in and out once again. Then quiet, then maybe a burst of activity around midnight, and so on until, near dawn, maybe 6:30, a whole lot of buzzing, touch-and-goes, and finally quiet as the Sun came up.

As you can see from some of the other posts here, I got really interested in capturing images of these bats during their nighttime routines. With the plummeting prices of video cameras intended for the security market, I was able to put up a camera to watch the area around the bat house 24 by 7.

Actually, I found this rather neat camera from SuperCircuits. It’s color in the daytime, not that there’s much to see around the bat house then. And at night it switches to monochrome and turns on a built-in Near Infra-red illuminator. That yields bright night time images in a light that we mammals, including bats, can’t normally see.

The camera says it’s weather resistant, but that’s assuming it under some sort of over-hang. So I built a little wooden roof attached the camera to it, and put the whole assembly up on a pole higher than the bat house.

Camera in weather-resistant housing

Here’s the camera, on its side as it’s being installed in the cover. Note my attempts at camouflage paint on the box – since the camera will be on a pole in a tree, might as well try a little subtlety for the benefit of the neighbors. The lens is in the center of the circular array of IR LEDs that supply the illumination once night falls.

A closeup of the camera installed on the pole, and extended into the tree beside the bat house.

Pole camera mounted in a tree

Actually, the corny-looking camo doesn’t do too badly in making the camera at least a little less obtrusive. Here it is from a distance:

Pole camera camoflaged in tree.

This video at the top of this post was shot using this camera, and another little monochrome camera mounted at the base of the bat house. Both shots, the one from atop the pole camera and the one looking up at the opening of the bat house are illuminated by the Infra-Red LEDs on the pole camera. Invisible to both the bats and us, they provide plenty of light for these scenes.

Hopefully the video clip provides a feel for just how fast these creatures are. Although they look like bright blurs in the video from the pole camera, that’s an IR effect and they’re basically dark brown, almost black in visible light. Maybe this is why lots of folks have never even noticed that bats probably fly over their backyard every night – it’s dark, they’re dark, and they’re passing by really quickly.

Imaging Bats with an Invisible Strobe

August 1st, 2010

Image of bat overhead

Looking and flashing straight up from my rooftop, this shot captures a bat in flight approaching the bat house. You can clearly see the fingers that support the membrane of each wing. The flash stops his (or her) motion completely.

The kind folks at Make Magazine published a short article I wrote about how I captured some of the images appearing on this blog. It’s in Make #20. Unfortunately they were looking for a maximum of about 750 words. When I’m waxing poetic about a subject that, like bats really interests me, I tend to overrun the editor’s limits. So here, with the permission of the magazine, is the full text from which the article was excerpted.

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September 26th, 2009

I thought I’d write a bit about bat houses, and I’ll start with my own. As you can see below, it’s showing some wear and tear from the weather. It’s been up over seven years now, and stood through several hurricanes.
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September 7th, 2009

Ducking in and out of the back door the other night, I was surprised to see something small and dark moving by the outside door frame. Probably a frog, I thought. We get lots of them on the glass sliding door during rainy summers like this one.

Then I shined the flashlight and looked more closely – yikes, a bat!
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They’re Back — or they never left?

August 16th, 2009

One reason I haven’t posted as often as I would like here is that I was feeling a bit depressed since it seemed that all or almost all the bats had rather suddenly left the bat house in July. The number of bat transitions — bats passing in or out of the bat house opening — had plummeted.

In June, I logged an average of 64 transitions per night, with at least a few detected every night. But in July, the number dropped to 38, and there were long runs of zero or very few ins and outs. Strange. By early this month, things were very quiet around the backyard.
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Graphs and Automation

July 13th, 2009


Making graphs is a lot of work, even if the subject is bats (and their songs). And while automated systems, like the bat logger, are a great boon in the unattended collection of information, they can pump out data at an alarming rate.
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Open-Source Bats

June 12th, 2009

Bat calls, “songs” to keep to the theme of this blog, are hardly inarticulate shrieks. In fact, bat echolocation calls are finely honed sonar pulses and have a complex and time-varying structure. The audio and rather low-resolution spectrograms in my earlier postings should hint at that.

There’s a fair amount of interesting scientific research out focusing on bat echolocation, in a much more systematic and detailed way. I was delighted to find not only the article below, but an entire on-line journal whose content is completely free, readily accessible, and freely redistributable.
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June 5th, 2009

Looks as if my explanation the other day for the high level of daytime excitement by the bats was both too pat and too optimistic.

It turns out that the individual whom I could see so clearly on the landing area of the bat house was not so much protective as in need of protection — this bat was injured and subsequently died.
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May 24th, 2009

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).
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May 18th, 2009

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.