Mountain lions and bears' eyes usually glow in the yellow-to-red range
You're walking to your stand in the darkness and the light from your headlamp reflects from a pair of glowing eyes in the distance. Is it a bear, a mountain lion, or some other predator that may want to eat you? Or do the eyes simply belong to a deer or perhaps a raccoon?
A recent article published by SummitDaily says it is sometimes possible to identify the animal behind the glowing eyes by the color and shape of the eyeshine.
According to the article's author, Frances Hartogh, who is a volunteer wilderness ranger for the Eagle Summit Wilderness Alliance, a reflective layer of tissue behind the retina called the tapetum lucidum causes the eyeshine. This layer reflects visible light back through photoreceptors in the retina, allowing light to stimulate light-sensitive cells a second time to improve night vision. This design provides superior night vision for some creatures, including nocturnal animals and those living underwater. Diurnal animals, such as humans and squirrels, do not have a tapetum lucidum.
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Eyeshine, which is a visible effect of the tapetum lucidum, enhances animals' visual sensitivity in low-light conditions by as much as 50%.
Eyeshine comes in blue, green, red, white, and yellow, and since eyeshine is a type of iridescence, color will vary with the angle at which you view it, the color of the light source, and the mineral content of the tapetum lucidum.
According to Hartogh, mountain lions and bears usually have yellow-to-red eyeshine range. Deer and elk's eyes shine white, while moose eyes tend to shine red. Rabbits and pikas have red eyeshine. Other mammals such as horses may have blue eyeshine, and the eyes of foxes, domestic cats, and dogs usually shine green, but cat eyes can also shine orange to red.
Hartogh writes that eyeshine color can vary by breed — and even within breeds. In domestic cats, varying amounts of zinc or riboflavin in the tapetum lucidum result in differing eyeshine color. And blue-eyed cats, like Siamese, often don't have a tapetum lucidum.
According to an article posted by Texas Parks and Wildlife (TPW), the majority of glowing eyes you may spot at night belong to mammals, but spiders, alligators, and bullfrogs also have light-reflecting eyes. Some night birds also have eyes that "glow in the dark," but their eyes do not have a tapetum layer. Scientists are still trying to figure out their source of eyeshine.
When trying to identify an animal at night by the shine of its eyes, Hartogh says you need to consider a number of factors:
- Height of the eyes above the ground
- Movement of the eyeshine — (is the animal hopping, weaving, leaping, climbing, flying?)
- Eye color, shape, and size
- Pupil shape — predators have vertically elongated pupils, while prey animals usually have horizontal pupils
For example, a black bear has large, round eyes that may give off a yellow to orange (but sometimes red or green) glow at night. Their eyes are nearly pupil-less and set close to the ground. Wild felines generally have a heavy upper eyelid and a perpendicular pupil. If you spot eyes shining a few feet above the ground, it's likely a deer or elk.