Are deer colorblind?
Deer possess dichromatic visionâthey see short-wavelength colors, such as blue and violet, and middle-wavelength colors, such as green, but they cannot clearly distinguish long-wavelength colors or those near the red end of the visible spectrum. This is because dichromatic vision depends on two types of light-sensitive cone cells rather than the three types responsible for color vision in humans.
How do deer see color?
Vision originates at the back of the eye, specifically in the retina. This thin layer of light-sensitive tissue contains photoreceptor cells, including cones and rods. Rods are especially sensitive to low levels of light and therefore serve important functions in allowing for vision at night and around dawn and dusk. Cones function best in brighter light and provide the basis for color vision.
Research on white-tailed deer (Odocoileus virginianus) and fallow deer (Dama dama) identified two principal types of cone cells, one that is central to perceiving short wavelengths and another most sensitive to middle wavelengths. Both species share a similar short-wavelength range, approximately 450â460 nanometers, with slight variation in sensitivity in the middle wavelengths. Thus, the visual system for both white-tailed and fallow deer is particularly responsive to blue and green wavelengths. This type of dichromatic vision is common among ungulates (hoofed mammals).
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In humans, a third cone mechanism provides for greater discrimination among longer wavelengths. Deer lack this additional mechanism, however, and thus reds, oranges, and some greens may not appear as distinctly different to a deer as they do to a human. This form of color vision is somewhat comparable to red-green color vision deficiency in humans.
How are deer eyes adapted for survival?
Despite weaknesses in the ability to distinguish between certain colors, deer have remarkable abilities in other aspects of vision. In particular, their eyes contain many rod photoreceptors, which heightens their sensitivity to dim light. For deer, this is especially useful, since there most active time of the day is during twilight. In such low light, visual detection of movement and potential predators is more important than being able to see a wide spectrum of colors.
Deer eyes also possess a tapetum lucidum. This layer of tissue, which lies behind the retina, reflects light passing through the retina, sending it back across the photoreceptors. The reflection through the photoreceptors improves night vision by allowing the deerâs eyes a second chance to detect light. The tapetum is responsible for the familiar shine produced when a deerâs eyes reflect light at night. With eyes located on the sides of the head, deer further benefit from a broad field of view. This arrangement helps deer detect movement and potential threats approaching from many directions; less binocular overlap is possible, however, relative to the forward-facing eyes of humans and many predators.
Does limited color vision benefit deer?
Dichromatic vision may be well suited to the environments and times of day in which deer are active. In natural landscapes, blue and green wavelengths, to which deer are specially adapted, generally are prominent. In addition, variations in the light available across a landscape are also thought to influence the movements of white-tailed deer.
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The reduced sensitivity to longer wavelengths in deer eyes also has a practical consequence familiar to humans: Blaze orange (sometimes worn by hunters and others) does not stand out to deer in the same way that it does to people. The color is conspicuously different from plants and other natural objects, to the human eye. A deer, however, less effectively detects orange, causing it to blend in with certain surrounding colors. Nonetheless, deer can still detect differences in brightness, movement, shape, and contrast.