Coyote Yipps

Lapis is a six month old pup born this year with one blue eye (the right eye) and one brown eye. She’s a beautiful if unusual coyote with slightly lighter fur than her siblings!

Apparently, blue occurs when there is a lack or reduction of melanin. Melanin produces brown eyes. This phenomenon occurs either due to genetic reasons or if there has been an eye injury.

At this point, I’m wondering if more could be going on than just a genetic color difference. There could have been an injury OR it might be that blue eyes have different anatomical properties than brown eyes in animals. In humans, for instance myself, blue eyes happen to be more sensitive to light than brown eyes — so there must be some, even if minor, anatomical difference. If blue eyes are more sensitive to light, I wondered if blue eyes see better at night than brown eyes. A Google search informed me that human blue eyes are more sensitive to light during the day, and by the same token, people with blue eyes tend to see better at night, unless there are bright lights. In other words, blue eyes allow more light into the retina. Wouldn’t this same physiology also pertain to animals? Biologist Carl Safina has pointed out that animals and humans actually have the same types of cells.

I ask this because Lapis appeared in one of my field infrared-lit cameras one night. See video below. Interestingly, her blue eye isn’t reflecting the light as well/as much as the other eye, in fact, the reflecting part seems to be a smaller circle of light than the brown eye, limited to the center of the eye. What is involved in the reflecting eyes is the tapetum.

The tapetum lucidum (Latin for “shining layer”) is the reflective surface in the back of the retina in some animals. It basically helps these animals see super-well at night by re-using the little light there is to maintain sharpness and contrast of an image on the retina — in other words, it increases the quantity of light passing through the retina by as much as 44%. It is also what causes the glowing eye phenomenon known as “eyeshine” which can be seen in night-vision cameras or when a flashlight is used. I see it in my nighttime infrared lit cameras. When there is an injury to the eye, this tapetum lucidum does not reflect the light — in fact, the animal looks like it has only one eye in the night vision cameras..

So there’s either a problem with the eye, such as an injury, OR blue eyes don’t form a fully reflecting tapetum surface because that would let in too much light. I’m coming to this conclusion based on this one case and offering it as food for thought and hoping for more input from other observers.

Further interesting reading on blue eyes. Unfortunately, I couldn’t find any articles on the quality of tapetum surfaces in blue eyes.