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Owl Night Vision

1-5-15  barn owlIMG_6003Like humans, birds have a sensitive retina in the back of their eyes that absorbs incoming light, senses it, integrates the information in it, and sends this information on to their brain. An avian retina is much thicker than ours and contains more rod cells (for dim light vision) and cone cells (for acuity and color vision).

As most owls are active at night, their eyes must be very efficient at collecting and processing light. The eyes of owls are disproportionately large compared to the size of their skull, and enable them to collect as much light as possible. In addition, the retina of an owl’s eye has an abundance of light-sensitive rod cells — owls have almost a million rods per square millimeter compared to humans which have only about 200,000. Barn owls can see a mouse at 6 – 7 feet with an illumination of .00000073 foot-candles – the equivalent of humans seeing a mouse by the light of a match a mile away. Eye size, an abundance of rod cells and additional neural mechanisms provide owls with vision greater than that of most of their prey.

Since owls have extraordinary night vision, it is often thought that they are blind in strong light. This is not true, because their pupils have a wide range of adjustment, allowing the right amount of light to strike the retina. Some species of owls can actually see better than humans in bright light. (Photo: barn owl, in captivity)

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13 responses

  1. Diane

    So interesting!

    January 6, 2015 at 2:01 pm

  2. Laura Andrews

    But if the mouse is holding the match . . .

    January 6, 2015 at 2:03 pm

  3. Suzanne Elusorr

    Mary,

    I love reading the ordinary, and yet utterly remarkable, facts about the creatures and plants around us that you offer every day. Today’s entry is just wonderful for its comparison of an owl’s abilities relative to a person’s. Again and again, what you allow your readers to glimpse is that the natural environment is not experienced as the same place for all its inhabitants – indeed, very far from it. Although we usually take reality to be as we perceive it, for each species, reality seems to be very different.

    Thank you so much for your blog,

    Suzanne

    January 6, 2015 at 2:08 pm

    • You’re so very welcome, Suzanne. Thank you for your very kind words, and for sharing my sense of wonder.

      January 6, 2015 at 3:20 pm

  4. Excellent. FYI: I recently photography a snowy owl in bright sunlight, perched on the ground. Upon seeing the image, most viewers assumed that it was at rest due to the nearly closed eyes and sleepy appearance. On the contrary, it was hunting, its head swiveling 360 and scanning constantly.

    January 6, 2015 at 4:08 pm

  5. micky

    Your photo is extroadinary!

    January 6, 2015 at 4:59 pm

  6. Mary, is there any evidence that the owl can see infrared light (long wavelength photons) so they might actually see the body heat of a mouse as opposed to moonlight or starlight reflected from the mouse’s body? Given that bees have ultraviolet-sensitive cones, and rattlesnakes have heat-sensitive cells in their “pits” that detect heat so they can see prey through bushes, etc, perhaps owl rods are receptive to “red” light that we can’t see.

    January 6, 2015 at 5:27 pm

  7. OMG! That is the best closeup I’ve ever seen – beautiful!

    January 6, 2015 at 6:56 pm

  8. Fascinating comparison – a mouse a mile away lit by a match – that is impressive! Nature is sooo amazing! Thanks, Mary!

    January 7, 2015 at 12:51 am

  9. Ruth Horton

    truly wonderful.

    January 7, 2015 at 9:10 pm

  10. Carol Yarnell

    A birding friend added this comment to your owl vision description….

    “It’s actually more complicated than that, as newer research has shown that it’s not just a matter of rods and cones, but the way the neurons are wired from the retina to the brain and how the signals are processed that also contributes to amazing visual acuity in very low light. Here is a very short version from Wikipedia. I couldn’t find the article that I had read not too long ago:

    “While it is commonly believed that owls have such great nocturnal vision due to their large (and thus very light-gathering) eyes and pupils and/or extremely sensitive rod receptors, the true cause for their ability to see in the night is due to neural mechanisms which mediate the extraction of spatial information gathered from the retinal image throughout the nocturnal luminance range. These mechanisms are only able to function due to the large sized retinal image.

    [18] Thus, the primary nocturnal function in the vision of the owl is due to its large posterior nodal distance; retinal image brightness is only maximized to the owl within secondary neural functions.[18] These attributes of the owl cause the nocturnal eyesight to be far superior to that of its average prey.[18]””

    January 8, 2015 at 10:45 am

    • Yes, thanks, Carol. I chose to use the words “additional neural mechanisms” in reference to this, as I try to keep my posts relatively short and simple!

      January 8, 2015 at 12:58 pm

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