Naturespeak A naturalist's view of the world

August 5, 2009

The Eyes Have It

Filed under: Uncategorized — wykes @ 10:43 pm

I got more than I bargained for when I returned to the Wilson State Park shelter at sunset. The ancient building, one of those stone & timber buildings probably built by the CCC in the 30’s, sat on the shore of Budd Lake. By day it served people, but it was also obvious that it served some of the natural inhabitants of the park as well.  The southeast corner of the structure showed evidence of a bat colony hidden somewhere within its attic space. At that location, the rock wall was spattered with guano –  bat droppings laid down by the tenants as they re-entered their belfry. I arrived shortly after sunset to see if I couldn’t see the bats exiting the colony. When I arrived, however, I found that I was not the first in line.

A family of raccoons were standing at the peak of the roof just to the west of the suspected bat lair (see above). There were three of them comprising a family of an adult and two good-sized young. They all looked a bit surprised at my arrival – expecting , no doubt, to have free and solitary reign of the place now that darkness was descending. I was not there to watch raccoons, so I too was a bit put out. I snapped a few shots just to pass the time before “bat-time” arrived.  Seeing the resulting eye shine pictures did get me to thinking about nocturnal vision for a moment (see another here). Normally, one doesn’t see this kind of view until just a few seconds before vehicular contact along a dark stretch of roadway.

Animals with reflective peepers, such as raccoons, have a layer in the back of their eyes called the Tapetum lucidum. This Latin term literally means “bright tapestry.”  It is sort of like a shiny space blanket composed of reflective crystals. The layer is located behind the retina, or focal point, of the eyeball and serves to reflect the available moon or starlight  back through the photo receptors of the retina.  The result is light amplification and excellent night vision. Lots of nighttime critters have this feature. Cats, dogs, opossums, owls, and deer count themselves among the lucidium set. That “deer in the headlight look”  is due to the back-lighting of this shiny eye tapestry. Raccoon eyes give off a yellowish glow, as do those of most cats and dogs. Occasionally, an oddball cat will have one yellow and one red reflective eye because they are handmaidens of Satan.

Our local bats do not have a lucidium tapetum, by the way. These creatures long ago replaced their need for night sight with an elaborate system of sonic pulses – they “see” with their ears, in other words. They can see alright during the day, but apparently can’t see any better at night than we can! I was able to confirm these facts as the darkness deepened and the bats started to exit from their lair. Normally bats begin their night flight about 12-15 minutes after sunset. On this night, that time was reached about 9:20 or so.

I wasn’t actually aware that the bats were even out until I snapped a few more flash shots of the befuddled raccoons. It was getting quite dark by that time. It quickly became apparent that the flashes were also freezing the images of some of the passing bats. They were invisible to my eye (which is also without a reflective night vision layer), so I just kept on blindly popping off the flash in the hopes I would catch a few of the bats in my camera frame. After all, they were the ones I was interested in. It took about a dozen tries, but I eventually came up with a few decent shots (see below and detail here).

The sight of a flying bat, wings and tail outstretched and mouth open, is a good thing. These fellows, which I believe were Big Brown Bats, were actively snapping up the flying insects that fluttered about my head. True to fact, not a single one reflected back any eye-shine. It was nice to get such solid confirmation regarding something you’ve read about. It was also nice to discover that I had inadvertently driven the raccoons back into their roof den. These reflective roof rats were apparently stunned by all the paparazzi flashing and elected to retreat until later in the night.

4 Comments »

  1. I love bats, what cool shots! There’s a park in Ann Arbor you can see bats at dusk, but not up close like this photo. Bats are amazing creatures, but unfortunately there are many myths about them. big and little brown ats are most common here and I’m guessing that is a big (even though they are pretty small, too. Their wings are thin as a plastic bag and they weigh about the same as five pennies!

    Comment by Monica the Garden Faerie — August 6, 2009 @ 9:07 am

  2. Cool. I like the cat observation too.

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