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Wednesday, April 11, 2012

The Eyes Have It

While we are waiting, I thought I would answer a couple of questions from viewers:

1)  Why does Momma look up?  Is she looking at the camera?

2)  And then one from a follower:  He commented about the tapetum lucidum whose visible effect is the eyeshine seen in the videos.  He asked whether owls were the only birds that displayed this feature.  Well that sent me to do some research because, to be honest, I didn't even recognize the term.  Here it is displayed in Momma's eyes in a video grab from last night:

First, the easy one.  Momma is not looking at the camera.  The light from the camera is in the infrared region of the spectrum and owls (like humans) can not see in the infrared.  She is looking up because there are tree branches above the nest box and Papa (as well as squirrels and other birds) sit up there.  She has very good hearing and I suspect that many times during the night Papa is above the box.  In some cases, he even sits on the top of the box, especially just before he delivers a meal.

Second, the tapetum lucidum is a layer in the eye that reflects light back to the photoreceptors on the back surface of the eye to improve night vision.  Humans do not have this layer but cats, racoons, and other mammals that are most active at night do.  You will see its effect as eyeshine in the headlights of a car.  Owls have this layer as well and it apparently also reflects infrared light as seen in the photo.  Do other birds have a tapetum lucidum as well?  The only ones I could find a reference to were the nighthawks and nightjars (Poorwills).

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