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SCV Outdoor Report: Cat’s Eyes

By Wendy Langhans


Sometimes we are stumped by the simplest of questions.  Like what happened earlier this week on our full moon hike at Towsley.  As we were talking about nocturnal hunters like bobcats and mountain lions, a teenager asked me this this question?  “Why do cats have slit pupils instead of round ones?”


Huh?  I was stumped.  My mind immediately flashed back to my training: “If you don’t know, admit it and say, ‘I don’t know but I’ll find out and get back to you.'”


The short answer:  it allows the cat to see in color at dusk and dawn.


The longer answer:  (caution, you are entering the science zone)


Cats are crepuscular hunters (between dusk and dawn), so their eyes need to work well in low light conditions.  According to a recent study, “For maximum light-gathering ability, the eyes of nocturnal and crepuscular vertebrates have pupils that are large relative to the focal lengths of the optical systems.”


If a small animal like a bobcat or house cat had an eye with a single-focus lens, this could pose a problem. A small eye has a shorter focal length and depth of field.  This would cause problems with color vision, since different wavelengths (colors) of light focus at different distances from the lens.  The result would be blurred color vision.


The solution is an eye with multi-focal lenses.  These lenses consist of different refractive zones that lie in concentric rings; each zone is tuned to a different wavelength.  This structure works well in the dark, when the pupil is fully dilated.  But how do you maintain sharp color vision at dusk or dawn, when the pupil constricts in response to sunlight?  A constricting circular pupil will, in effect, limit color vision by blocking the outer lenses.


You solve this problem by using a slit pupil.  A constricting slit pupil will still span all the lenses, providing sharp, focused color.  And it’s certainly a better solution than the bifocals I wear now.  Even better than Lasik, don’t cha’ think?



Upcoming Outdoor Events:


Saturday, July 11th and 25th, and every Wednesday, 8:00 AM.  Trail Maintenance Volunteers at Towsley Canyon.

Come join our trail maintenance volunteers for camaraderie and a heart-thumping workout.  For more information contact Steve Ioerger at 661-291-1565.


Saturday, July 18, 8:00-10:00 AM.  Bird Hike in Towsley Canyon.  Wear close-toed shoes and bring water.  An easy walk, suitable for families. For map and directions go here.

Sponsored by the Mountains Recreation and Conservation Authority.



You can listen to stories like this every Friday morning at 7:10 a.m. on “The Hike Report”, brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.


For the complete MRCA hike and activity schedule and for trail maps, click here or go to

SCV Outdoor Report: Cat’s Eyes

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