COLUMN: Nocturnal vision: some animals have the edge

THE NATURE OF THINGS COLUMN
By: 
Michele Olson
Jones County Naturalist

     Have you ever stubbed your toe, had a deer suddenly appear in front of your vehicle, or had a horrible time finding the keyhole in your door after the sun sets and darkness descends? Maybe you’ve wished you could see in the dark? Many of our nocturnal wild animal neighbors do just that with some very cool adaptations for nocturnal vision.

     I’m sure you’ve noticed many animals of the night have big eyes. All the better to see with – right? Many nocturnal creatures like owls, cats, flying squirrels, and tree frogs have large eyes with pupils that when wide open, cover almost the entire front of their eye.  These large eyes help to capture more light from the stars, moon, and any other available light source helping to improve their night vision.

     The eyes of many nocturnal animals contain higher concentrations of rod cells in their retinas that allow them to see movement and gather basic visual information in low light situations. In addition, many nocturnal animals have rod cells that are specially designed, with the middle of each rod cell being very dense/thick, helping to focus light in very low light situations. This increased sensitivity to light makes it much easier for these animals to detect even the smallest movements in the dark.

     To aid in creating images at night, some animals have a layer of reflective cells, called the tapetum, located behind the retina. This helps to reflect back photons of light not captured by the rod and cone cells the first time. It also creates the eye shine we see when our headlights, flashlights, or headlamps shine into the eyes of a nocturnal animal. It’s interesting to note that different animals have different color tapetum which can aid in nocturnal animal identification. Rabbits and weasels eye shine looks reddish in color while dogs, cats, and coyotes have a greenish eye shine, deer and raccoon have a yellowish eye shine, and fox have a whitish eye shine.

     Nocturnal creatures often have other highly developed senses that can include hearing, touch, or smell to complement their vision and help them to “see” in the dark. Little brown bats for instance use echolocation to navigate and find their prey in the dark. Barred owls have an extremely developed sense of hearing to hunt voles in the meadow on even a cloudy night. Many snakes can sense the changes in temperature to find a mouse hiding in a log. Raccoons can feel with their fingers along the rocks in a stream for a crawdad meal.

     You might have a greater capacity for seeing at night than you realize. To test your night vision try going for a stroll at dusk, just as the setting sun is painting the skies and fields with beautiful colors. As you walk along your gravel road, field edge, or wooded path, your eyes will gradually adjust to the amount of light available and you will become more aware of your other senses as they too try to compensate for the lack of light. You will become aware of your surroundings in a new way, giving you confidence and a new appreciation of the night.

 

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