Eyeshine

Tracks and scat may be the most common signs of PEI wildlife, but they are not the only ones. Other examples include dens, nests, cavities, caches, browse, and this very cool adaptation: eyeshine.

Not all animals have eyeshine, but those that do have a special membrane called the tapetum lucidum (Latin for bright tapestry) behind the retina – the light-sensitive part of the eye. Light passes through the retina and is reflected off the tapetum lucidum back to the light source. This reflection gives the retina a second chance to absorb that light, effectively increasing the amount of light available for vision. Animals with eyeshine also have more rods (light receptors) and fewer cones (colour receptors), sacrificing colour vision for better night vision.

Not all eyeshine is the same colour because not all tapeta lucida have the same structure and chemistry. This can vary not only among species, but also among breeds: for example, my Golden Retriever’s eyeshine is (appropriately) gold, while that of my two Shiloh Shepherds is bluish-white. 

My favourite colour of eyeshine is red, caused by a high concentration of blood vessels in the tapetum lucidum. Barred Owls have strong red eyeshine, and there’s nothing quite like seeing glowing red eyes above you in a tree at night! (This is similar to, but not the same as, ‘red eye’ in photos of humans; we don’t have a tapetum lucidum).

Most of PEI’s wild mammals - with the exception of red squirrels and bats - have eyeshine. Eerily, spiders, fish, and some frogs also do. (I know if I hold a flashlight at eye-level and look through the grass on a summer night I can see spider eyeshine, I’m just pretty sure I don’t want too!)

Knowing the height and colour of eyeshine can help identify who is looking back at you from PEI Untamed!