Sunday, May 18, 2008

Sounds in the Silence


Shortly after nightfall I am sitting in the back yard, enjoying the heat rising from the patio. Besides the gentle rustle of the Japanese maple and the lonely call of a Pacific Chorusfrog in some distant neighbour’s yard, there is the faint crackle of static, which suddenly erupts into a loud staccato series of clicks. My bat-detector has detected its first bat of the evening!

Bat-detector? Strictly speaking, it’s an ultrasound detector, an electronic gizmo not much larger than a deck of cards that converts sounds far beyond the range of human hearing to sounds audible to our ear. Were Wile E. Coyote to hunt bats rather than roadrunners, he would have had one of these things mailed to him from ACME. I purchased mine from Bat Conservation International.



Bats are remarkable for their use of sound as a hunting and navigational tool. They emit pulses of sound from their mouth, or nose, at frequencies of tens of thousands of cycles per second, which bounce off objects, including tiny moving prey, in a near-lightless 3-D environment. From the strength and frequency of the echos, like a Doppler radar, they can determine distance, speed and direction of travel of a target. Once prey is in range, the bat produces a “feeding buzz,” a rapid increase in the rate of sound emission that allows it to home in on an airborne bug. It would be like glimpsing something far ahead in your headlights and having the immediate ability to train a powerful search light on it and then reach out the window and grab it. It is done in fractions of a second by an animal the mass of a plum.

A Red Bat, a species found in southern BC, can consume up to 100 moths in a night, which is important in reducing the numbers of caterpillars that attack crops and forests. Others are voracious mosquito eaters, consuming up to a thousand per night. In other parts of the world, bats are key in pollinating a wide variety of human food plants, including those common on North American grocery shelves.

One quarter of all mammalian species are bats. This prolific evolutionary design takes advantage of the fact that in warm places there are vast numbers of protein packets (insects) flying around in the dark, and very few large, flying predators. However, bats are in decline everywhere due to the loss of forests that provide day roosts and places to raise young, loss of wetlands, and even the loss of old wooden man-made structures, such as rural churches, barns and bridges that serve as nursery roosts for colonial species. Nine of the 17 bat species in BC are threatened with extirpation or are vulnerable to continued population decline, and it is suspected that the remaining eight may also be in trouble.

But still we have bats on this island, at least a few. A walk to the closest neighbourhood park, bordered by ditches, yields a few more hits on the bat-detector. I expect a lot more could be heard along the city’s sloughs, dykes and around the larger ponds.

4 comments:

April said...

I read with interest your post about bats and have bookmarked the Bat Conservation web site for reading later. We have a lot of bats here - I think they are the little brown bats. Plus, we have tons of mosquitoes - I'm always grateful for the bats and their appetite for these biting insects. So far I haven't seen any this year, but I expect them soon.
P.S. Thanks for helping me out with the mystery animal id. I think it's a fisher, too, after doing a bit more research and from your information re: colour. They do inhabit these forests. :)

BerryBird said...

I live in the range affected by white nose syndrome (also discussed on the BCI page). Losing 90% of our cave dwelling bats is a terrifying prospect.

Hugh said...

April, You're most welcome for my input on the i.d. It's fantastic that you were able to get such clear photos. I envy you your local wildlife! You probably have several bat species in your area, including Little Brown. Those small brown Myotis species are hard to tell apart.

BerryBird, I had not heard of white nose syndrome (when I first read your comment, I misread it as "white noise syndrome," which I guessed to be some sort of urban noise pollution.) What a frightening prospect. Bat biologists and others in the US have done so much over the past several decades to shore up eastern bat populations ... and now this. It's the nightmarish bat equivalent to the chytrid fungal infections that are decimating frog populations.

Our planet is not well.

chey said...

I left my comment for this post under your Blue Bangles post by mistake. We have lots of bats here in Nova Scotia. The kids love to watch them at dusk. Interesting device you have there!