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A Parrot's Eyes

Discussion in 'Bird Boulevard' started by jamie, 10/17/09.

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  1. jamie

    jamie Rollerblading along the road

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    This is a summary of a part of a chapter from "Manual of Parrot
    Behavior". The title of the chapter is "Sensory Capacities of Parrots"
    and the authors are Jennifer Graham, Timothy F. Wright, Robert J.
    Dooling, and Reudiger Korbel. It is a very interesting read.

    As many of you know a bird's vision is from 2 to 8 times stronger than a
    mammal. Birds eyes are relatively large in relation to the size of
    their skull. Because of this their eyes allow a relatively large image
    to be focused on their retinas. They also have a higher density of
    "cones" than humans. The authors give an example of a hawk which has
    300,000 cones per square millimeter whereas humans have around 147,000
    cones per square millimeter. "Cones" are cells within the eyes that
    detect daylight and colors. Also, in a bird's eye, nearly every cone is
    represented by an individual axon to the bird's brain. An "axon" is a
    nerve fiber- so essentially, each cone in a bird's eye has a direct wire
    to its brain. In humans, we may have from 6 to 7 million cones, but
    only a million axons in our optic nerves- meaining we have fewer light
    receptors and several of those receptors all share a single wire to our
    brain.

    A parrot's eyeball is also flattened whereas ours are round. Their eyes
    project a relatively smaller image when compared to other birds- especially birds of
    prey. Also, we all know that a parrot can turn its head nearly 180
    degrees to look around in all directions. This makes up for their lack
    of eye movements.

    Also, different from humans, a bird can directly control the dilation of
    its eyes- and many of us can see this when our birds "pin" their eyes
    when they are excited. Parrots often rapidly dilate and constrict their
    pupils when they are being aggressive or are excited. Humans can not
    willingly dilate or constrict their pupils. Birds do have "pupillary
    light reflexes" but they are not the same as they are in humans.

    Unlike humans, birds do not have blood vessels in their retinas.
    Instead, they have a structure called a pecten which many scientists
    belive noursihes retina cells and keeps them alive.

    We have all noticed that when a bird is seriously studying something it
    will turn its head or body sideways and focus one eye on the object of
    interest. Behaviorists have found that birds have better lateral vision
    than they do frontal vision and they take advantage of "monocular"
    vision for that reason.

    Another neat thing about birds eyes are that they are either
    "tetrachromatic" or "pentachromatic" depending on the species. Human
    eyes are "trichromatic". That means our vision is based on three
    colors- red green and blue. Bird eyes can detect ultraviolet
    light, fluorescent light, in addition to red, green, and blue light. In
    fact, many scientists believe that their ability to see ultraviolet
    light is related to their behaviors. Many feathers reflect UV lights
    and studies have shown that UV reflection can affect mate choice. UV
    reflection from feathers and skin can vary between sexes in some
    species- and even though we (humans) can not tell the difference,
    viaually, between a male and female in many species, a bird can. Also,
    some types of fruits reflect UV light and the amount of light reflected
    is indicative of the ripeness of the fruit. So, a bird can tell how
    ripe a piece of fruit is and decide if he wants to eat it or not (maybe that explains
    some of out picky eaters!!! :D ). The same is true for flowers.

    Some babies have UV reflective cells in their mouths that tell their
    parents where to stick their beaks at feeding time! Gouldian finches
    are a great example of this.

    Another interesting fact about birds is that they can detect a spatial
    frequency of about 160 frames/second (or Hertz (Hz))- compared to 50 or 60
    Hz in humans. That means that some "stroboscopic" effects
    that humans may not be able to see ARE visible to birds. Artificial
    lights often do not produce continuous light- meaning that they produce
    light in very short bursts like 100-120 Hz. We can not see this but our
    birds can. Also consider that many televisions refresh their screens at
    a rate of 50-95 Hz, so our birds may be seeing more "choppy" motion than
    we do if they are watching television with us or looking over our shuolders
    when we are at the computer.

    Many scientists are not sure what effects this might have on
    birds. However, you can help improve your bird's welfare and living
    conditions by providing full spectrum lights, normal light cycles, and
    continuous emitting light sources
     
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  2. Angelicarboreals

    Angelicarboreals Rollerblading along the road

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    Is that book one that you picked up somewhere? Sounds like a great read to me.
     
  3. Patricia

    Patricia Jogging around the block

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    Wow,great info thereā™„
     
  4. Braekedaun

    Braekedaun Sprinting down the street

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    That was awesome, thanks!
     
  5. birdlady

    birdlady Joyriding the Neighborhood Celebirdy of the Month Avenue Spotlight Award Avenue Veteran

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    Some interesting info there Jamie. Keep it coming!
     
  6. JLcribber

    JLcribber Joyriding the Neighborhood Celebirdy of the Month Mayor of the Avenue Avenue Spotlight Award Avenue Veteran Shutterbugs' Best

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    Good stuff Jamie. IMO that's why it's so important to have nice bright full spectrum lighting for our birds so they can see their world the way it's supposed to be seen. :)
     
  7. Braekedaun

    Braekedaun Sprinting down the street

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    so what would eliminate the light cycling? what kind of light? is that referring to the old tube type flourescent and not the CFL?

    Other than obviously sunlight! :rofl:
     
  8. Big Blues

    Big Blues Rollerblading along the road Avenue Spotlight Award Avenue Veteran

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    Interesting information, thanks for posting.
     
  9. akijoy

    akijoy Rollerblading along the road Mayor of the Avenue

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    Fascinating stuff. Explains why they don't miss a thing...even a grain of rice from across the room.
     
  10. Welshanne

    Welshanne Cruising the avenue Celebirdy of the Month Mayor of the Avenue Avenue Spotlight Award

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    Yes have discovered the broad spectrum lighting is much more important to the wellbeing of our feathered friends than I had first realised.
    Besides the bird being able to see their world in the hues and colours that they should, it also acts on their skin/feathers to convert their foods into the important vitamins that they need to live a healthy life.
    Although Leroy was being given the correct diet, she was ill because her body was unable to convert it into her needs, without the lighting.
    Once she was provided with it, it was as if a switch had been put on inside her and she started immediately to respond and function properly because of it.
    Maybe because she is a weak Grey from hatching and will always need extra care and attention because of this, it has shown it up more, no idea.
    Loved reading this info thank you for showing us. :hug6:
     
  11. CarmieJo

    CarmieJo Rollerblading along the road Avenue Veteran

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    That is interesting.
     
  12. Gen120

    Gen120 Joyriding the Neighborhood Avenue Veteran

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    wow, awesome! Thanks for the info Jamie!:hug8:
     
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