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What Do Rabbits See?
by Dana M. Krempels, Ph.D.
Many house rabbit "parents" are curious to know what the world looks like to
their lagomorph companion. Why does it seem difficult for my bunny to find food
right in front of his face? Why is my bunny so easily startled or frightened if
I walk into the room holding a box or a grocery bag? Can my rabbit see colors?
The first thing to remember is that a rabbit's visual system evolved under
evolutionary pressures completely different from those which "designed" your
eyes. We human primates, like our simian cousins, have forward-placed eyes which
confer binocular vision and depth perception. This is essential for an animal
originally designed to leap through the trees. Also, we have excellent color
vision, a trait which helped our ancestors to find ripe fruit and tasty flowers
in the forest canopy.
On the other hand, the rabbit visual system is designed--not for foraging and
locomotion--but to quickly and effectively detect approaching predators from
almost any direction. The eyes are placed high and to the sides of the skull,
allowing the rabbit to see nearly 360 degrees, as well as far above her head.
Rabbits tend to be farsighted, which explains why they may be frightened by an
airplane flying overhead even if their human companion can barely see it. (It
could be a hawk! Run!)
The price the bunny pays for this remarkable field of vision is a small blind
spot directly in front of his face, but forward-placed nostrils and large,
spooning ears compensate for that minor loss of predator-detecting space. For an
animal to have binocular vision, the field of view of both eyes must overlap to
some degree. The central blind spot in the rabbit's field of view precludes a
three-dimensional view of nearby objects. When your bunny cocks her head and
seems to be looking at you "sideways," she is actually looking as straight at
you as is possible for a bunny. As far as we know, she does not have a primate's
level of depth perception at such close range.
What about color vision? In general, vertebrates have two different types of
photoreceptor cells in their retinas: rods and cones. Cones confer high
resolution, and, if more than one cone type is present, they also confer the
ability to perceive various wavelengths of light as distinct colors. For
example, we humans have three different categories of cone--their maximum
sensitivities in the red, blue and green regions of the spectrum. The differing
sensitivities of each cone type enable us to perceive different (visible)
wavelengths of light as the colors of the rainbow.
Behavioral studies published in the early 1970's indicate that rabbits do have a
limited ability to discriminate between some wavelengths of light, perceiving
them as different colors. Evidently, they can discriminate between the
wavelengths we call "green" and "blue." Although rabbits may not perceive green
and blue the way we do, they *can* tell them apart. This means they have limited
color vision, probably conferred by two different categories of cone cells (blue
and green).
The other type of photoreceptor, the rod cell, confers high visual sensitivity
in low light situations, but relatively poor resolution (i.e., a "grainy"
picture). The rabbit retina has a much higher ratio of rods to cones than the
human retina has. Although a rabbit can see better than a human in low light
conditions, his low light image has much poorer resolution (clarity) than the
daytime images formed by your cone-rich, primate retina.
Now you may wonder: "Can my rabbit see me clearly, or am I just a big blur?" As
you read this page, you are focusing on the letters with a very tiny part of
your retina called the fovea. This is a minuscule, cone-shaped depression in the
retina, lined wall-to-wall with high resolution cone cells.
Rabbits, too, have small retinal areas with more cones than rods. However, this
(italics) area centralis (close italics) is not indented, and it has far lower
cone density than our fovea has. The image formed by the area centralis is
relatively "grainy" compared to the one formed by your fovea, but it serves the
rabbit well. Using this image, your voice, body movements and scent as cues,
your rabbit can recognize you (his favorite human)--as long as you're not
carrying a scary box that completely changes your familiar shape!
Knowing a little more about how another creature sees the world allows us to
come one step closer to understanding its behavior--and modifying our own to
make life happier for everyone. Remember that the next time your rabbit gazes at
you with those deep, ancient eyes.
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