I just got back from data gathering at several southern natural history
collections, and I have to admit I am somewhat burned out from all the
"fun." It was impossible for me to check my mail, or read the FML, and my
mail folder looks like a bomb went off.  I even had the dreaded "You are
over your limit in MB; older files will be deleted" notice.  It will take
some time to get to each one and respond, and if I don't in the next week or
so, let me know.
 
I missed the stuff on carnivores, so I'm not really sure of what was said on
the FML, but I had five e-mails asking me to clarify the matter.  The way I
understand it, some zoo technician stated ferrets were omnivores and fed
them a fruit-meat mixture.
 
First, the digestive system of the ferret is very short.  There is no caecum
(a pouch or tube at the junction where the large intestine meets the small
intestine), nor appendix, and the junction between small and large bowel is
not visually apparent.  This is not uncommon in highly carnivorous mammals,
including sea mammals and many specialized carnivores.  In contrast, the
caecum of herbivores is often very large, and can form pouches quite long
relative to the length of the large intestine.  The determining factor in
the length of the caecum appears to be the amount of ingested cellulose in
the typical (averaged) diet.  The more cellulose ingested by the species,
the longer the caecum tends to be.  The ferret's problem in digestive plants
are twofold; first they lack a caecum to hold the bacteria which breaks down
the cellulose, and second, they lack several of the enzymes found in the
rumin of most plant-eaters.
 
Second, there are VERY few "true" carnivores or herbivores.  The vast
majority of mammals are omnivores in practice; the name is generally applied
according to the major dietary preference.  Compounding the misunderstanding
is the name applied to a group of mammals that are generally meat-eaters;
the Carnivora.  Many Carnivora are in fact herbivores (pandas) or omnivores
(bears, raccoons).
 
Third, any animal can be fed an "unnatural diet" and survive.  It happens
all the time.  The animal may have health problems, a shortened life,
depressed reproductive ability, etc., etc., but it can survive.  I have read
authorative accounts indicating ferrets should be fed "sops" (milk and
bread) or cooked cereals, and they survived.  But it is not an optimum diet,
nor does it promise the healthiest and best possible life for the animal.
Additionally, starving animals will consume just about anything to survive.
I was once asked to perform a necropsy on a dog found dead at a kennel.  The
kennel people claimed the dog was ill, but I found bits of rubber, stones,
sticks, grass, and nails in the dogs stomach and intestine.  The dog was
ingesting anything it could find to sate it's hunger, including eating
portions of a garden hose.  Lacking meat, most carnivores will eat
vegetation to get by.
 
Fourth, ferrets inprint on foods at a very young age, which means they can
learn to eat foods that would not normally be part of wild animal's diet.
So just because a domesticated ferret can learn to eat an artichoke (Bear
loves them) doesn't mean it would sustain them in a wild state, nor would it
even be seen to occur except perhaps by starving animals.  Trust me,
whatever Bear eats does not change much; it would not be enough to survive.
 
If you were in my lab, I could show you Cuvier's trick; a generally accurate
way of determining the diet and carnivory/herbivory ratio for any animal.
You just look at the teeth.  The ferret has four molariform teeth; one in
each quadrant.  The lower molariform teeth are nothing more than tiny pegs,
each slightly smaller than the head of a sewing pin.  The upper molariform
teeth are about 1/3 the size of the largest tooth in the mouth, which is a
cutting tooth called a carnasial (or sectorial) tooth.
 
This indicates that while the ferret primarily cuts meat (carnivores do not
technically chew food--they cut it with the carnasial and swallow the
pieces), it does eat things that require crushing.  This includes insects,
snails, spiders, fruits, berries, and nuts.  The cellulose in the vegetation
passes through, and the ferret claims the carbohydrates, vitamins, and some
proteins.  Like most mammals, ferrets crave the high energy and low
work-cost of many fruits, and rely on their sugars to build the fat reserves
to make it through the winter.  (Yes, I know ferrets are domesticated, and
so are we, but we both suffer from a physiology that still thinks we live
hand-to-mouth in the wild.) As a professor once told me about temperate
carnivores, "...meat allows them to maintain their bodies and reproduce, but
sugar allows them to survive the winter."
 
Under these circumstances, many people would claim the ferret was an
omnivore, but that would be incorrect.  Fruits, berries, and nuts are only
available for a short time; the major portion of the year is spent eating,
you guessed it, small rodents, leporids, amphibians, fish, and insects.  The
ferret is as true a carnivore as they come, second perhaps to the vampire
bat or sea mammals.  (interestingly enough, mink lack a caecum, while cats
have one; so if you classify a ferret as an omnivore, you will have to
include mink and cats).  In reality, food preferences form a continuum with
pure herbivory at one end and true carnivory at the other.  Ferrets are at
the top of the carnivore end.
 
So what about the food given by the zoo-guy?  As I understand from the
e-mails, it is a fruit and meat mix.  As long as the ferrets are getting
enough protein, I don't see a problem.  True, too much of a good thing can
cause the dreaded "raisin runs," but if the animals were in an unhealthy
state, it would be obvious.  What concerns me more is his misunderstanding
of biological priciples, and his reliance on them to support a law based on
political motivations.  I would recommend speaking with this person, if
possible, and gently educate them to the truth.  Perhaps you can give them
an introductory text to mammalogy.
 
I hope I understood this question right.  If not, I quote Gilda
Radner..."Never mind." I'll get caught up by this weekend. Maybe.
 
Bob and the 13 Nonherbivorians
[Posted in FML issue 1521]