[Two-part post combined.  BIG]
 
Because of the timing of eye growth in newborn kits, vision in the ferret
has been extensively studied as part of ongoing research into the
development of the eye and associated structures.  When discussing odor
in ferrets, I mentioned it was a very important sensory system, so much
so that it rivals vision in primates.  That is NOT to imply vision is
unimportant; it is just not a dominant as it is in some other animals;
sort of like the sense of smell--compared to vision--is in humans.  For
example, humans identify each other visually, but ferrets use scent for
personal recognition (SOME recent research suggests the ferret's cryptic
facial markings may come into play for personal identification of litter
partners, but it remains an unsupported hypothesis).  Nonetheless, visual
clues are VERY important to ferrets; the open play mouth, the weasel war
dance, and the play bounce are all VISUAL clues to let other ferrets know
aggression is meant for play, not injury.  Understanding the differences
in vision between humans and ferrets can go a long way towards building
an effective enrichment program.
 
One observation that always struck me as odd was the way my ferrets
would react if I quietly entered their room.  The moment my motion was
detected, most of the ferrets would freeze and quietly stare in my
direction, but some would take off like a bat out of hell.  However, if I
used my VOICE to announce my arrival, my sudden visual appearance rarely
caused such reactions.  It was clear my ferrets recognized my voice, but
why didn't they recognize me?  The answer to that question lies in the
comparative structure of the human and ferret eye.
 
Both humans and ferrets have eyes that are structurally similar, but
there are some important differences.  In both human and ferret eyes, the
retinas use rods and cones to detect light.  Rods are 10,000 times more
sensitive to light than cones, but only see in shades of gray and do a
mediocre job of recording fine details.  Cones sense color, depending on
the number and types of pigments they contain, and produce sharp vision.
Having cones in your retina does NOT mean you see in color--they may be
present only for recording sharp images in good light.  In humans, the
cones in the retina have three pigments, giving us trichromatic vision.
Ferrets have only two pigments in their cones, producing dichromatic
vision.  Like horses, ferrets are green-yellow colorblind, seeing only
reds and some of the higher-end blues.  Humans have round pupils, but
ferrets have pupils that constrict to a horizontal slit.  A slit allows
the pupil to open to large diameters compared to the size of the eye
(cats have similar pupils, only they open vertically).  The horizontal
orientation of the ferret pupil improves visual acuity within the
horizontal plane.  Humans, well, maybe not me, but the average human has
20/20 vision; ferrets are similar to cats, having vision in the range of
20/100 to 20/200 (depending on the researcher).  Unlike *MY* left eye's
20/200 vision, objects beyond the ferret's range of visual acuity are not
blurry; they are just featureless, lacking detail (why my face is hard to
recognize when I suddenly appear).  Humans have a field of vision that
encompasses 180 degrees of coverage, like that of an orange cut in half,
while ferrets, like dogs, have a field of vision coverage ranging from
240 to 300 degrees (again, depending on the report).  Humans have 140
degrees of coverage within their binocular field of vision, but ferrets
only have between 90 and 110 degrees of binocular coverage.  One other
difference is that humans can see objects as they enter the mouth, but
ferrets cannot; their comparatively massive nose blocks that angle of
view.
 
Complicating the issue are albino ferrets; they have enough differences
in their visual system compared to sables that it is sort of like
describing the eyesight of another species.  Albino ferrets have
diminished color vision, less visual acuity, and several "wiring"
defects making their vision inferior to their pigmented peers.
 
There is one other factor that recent research has illuminated; the
effect of the visual environment on the development of the ferret retina.
There is a tremendous amount of evidence that has shown that what the
kits SEE can influence the orientation and placement of the ganglia (and
associated cones and rods) within the structure of the retina.  This is
comparative new research, but it does give rise to questions regarding
eye development in kits housed in visually sterile environments, such as
those experienced by most of the ferrets in the Americas.  It is possible
that reported visual differences between ferrets and polecats are
environmentally caused, rather than genetic in nature.
 
The bottom line is ferrets experience a different sort of vision than
that seen in humans, so our visual enrichments need to reflect those
differences.  Some tips to learn BEFORE trying visual enrichments can
be of help.
 
1. Since the cones in the ferret's eye require much more light than the
rods, try increasing illumination to increase visual acuity.
2. Color is far less important than contrast; try to place darks next to
lights, rather than medium greens next to medium blues.
3. Ferrets may not be able to see a mouse on the floor if it is not
moving, but they can sure detect it if it runs away; try using movement
in the enrichment.
4. Ferrets see better along the horizontal plane rather than the vertical
one, so bring the enrichments down to their eye level.
5. Ferrets see sharpest between 4 inches to a foot in front of their
nose, so bring the enrichments closer.
 
1. Graphic Balls: Buy a large plastic ball of a light color.  I like the
cheap 18 inch diameter plastic balls sold at Walmart for 3-4 bucks.
Using black magic markers, draw SIMPLE graphic designs on the ball, such
as lines, squares, triangles, circles, etc., so that about half of the
ball is covered with contrasting designs.  Just place the ball on the
floor and watch the ferrets show more than simple interest.  For
heightened enrichment, combine vision with odor, and rub the ball
with different odors in different locations.
 
2. Ferret Fishing: Take one cheap, white linen hand towel, and cover it
with black squares drawn with a magic marker.  Tie a knot in one corner
of the towel, then tie a string under the knot so it will not slip off
when the towel is tugged.  Tie the other end of the string to a wooden
dowel or a broomstick, and go "Fishin' Fer Ferts." The linen hand towel
has a fine mesh that helps prevent snagging claws, and is preferable over
terrycloth.
 
3. Hittin' The Sack: Use black magic marker to draw graphic designs on
an old pillowcase (I get them at thrift stores).  I put a couple ferrets
on the bed, then flap the pillowcase over their heads, drop it on them,
play tug of war, and even put them in the case and drag it around.
 
4. Pong, The Game: I use four-dozen ping-pong balls, half of which are
painted black, poured into a plastic tub.  Need I say more?
 
5. The Weasel In the Sky Keeps On Turning: Most builder-supply stores,
such as Home Depot or Lowes, have fairly cheap unfinished plywood or
pine circular tabletops.  I use one that is 2.5 feet in diameter that
I have painted with white and black graphic designs.  Drill four holes
equidistant along the edge and attach four eyebolts.  Tie nylon line to
each eyebolt, and then tie the four lines together at the other end with
an overhand knot.  Attach a hook to the knot and hang the table.  Your
ferrets will know what to do.
 
6. Feed My Ferretstein: Take one cheap oven mitt, attach eyes and mouth
details that graphically contrast with the mitt, and play "Kill the
Monster." The wrestling is tactile enrichment, the play is bonding
enrichment, and the graphic eyes are visual enrichment.  Your fingers
are protected from hard bites and you enrich the life of your ferret;
you can't lose and neither can the ferret.
 
Bob C
[Posted in FML issue 4208]