This seems to be timely of late, so I moved it ahead of sequence.
 
Q: "I was told ferrets only live about 6 years. Why don't they live as
    long as my cat?"
 
A: They tried, but they're not dumb enough.
 
The theoretical length of any mammal's life is tied to several things,
including environmental factors, DNA degregation, other genetic factors,
metabolic rate, hierarchical dominance level, nutritional state, and stress
levels.  Each one can have a significant impact on the lifespan, making the
whole question quite complex and impossible to predict for the individual.
Even at best, lifespan estimates are nothing more than "guestimates," based
on probabilities.  There is no way to predict the lifespan of any given
individual.
 
Despite lifespan prediction complexity, there are recognized limits to a
species lifespan.  Centuries ago, naturalists noticed the smaller an animal,
the shorter it's life.  Elephants lived longer than cows which lived longer
than dogs which lived longer than cats which lived longer than rats which
lived longer than shrews.  What it didn't take into account was metabolic
rate.  The metabolic rate is determined by the amount of energy it takes to
maintain body temperature and biochemical reactions for a given
environment/climate and diet.  The higher metabolic rate usually translates
as a shorter lifespan.
 
That is what you see in ferrets.  Ferrets are long and thin compared to dogs
and cats.  You might remember from your basic biology that animals of the
same species tend to get bigger as you travel north, partially because a
large rounded mass tends to conserve body heat during harsh winters.
Conservation of body heat = lowered metabolic needs = lowered food
requirements.  Because the ferret's body is long and thin, it tends to lose
heat faster than plumper animals of the same mass.  Long skinny animals have
compensated for heat loss by having the internal metabolic rate run a little
higher, which also results in a need for more food.
 
Look at how a cold cat or dog sleeps.  They roll into a spheriod ball shape,
but the best a ferret can do is make a flattened disk.  Spheres have the
smallest mass-to-surface-area ratios, so they lose less heat.  Disks lose
much more heat.  Ferrets use a higher metabolic rate to make up the
difference, so have to eat more and higher fat foods.  They also are experts
at conserving energy, sleeping as much as possible-- up to 20 hours a day
when it's cold -- which is also why the winter coat gets so thick.  To
conserve energy, the ferret drops into a very deep sleep, and slows down its
metabolic rate, which is why they shiver when they wake up.  This is also
why ferrets are poop machines with the amounts of food they eat, especially
in winter.  Carbone eats more than my cat, who outweighs him by 20 pounds.
What goes in comes out.
 
High metabolic rates result in faster heat beats per minute, higher body
temperatures, and increased respiratory rates.  They also have shorter
lives.  This is sort of a long-bones-means-tall-people phenomenon.  You
know, long bones = tall people, but tall people are not tall because of
their bones.  Same here, high metabolic rates = short lifespans, but the
causality is something else besides the metabolic rate.  Incidentally, this
is a key to why insuloma (and even adrenal disease) effects ferrets so
profoundly compared to the other animal pets.
 
In the wild, both polecats and ferrets only live 2-3 years, with a maximum
at about 5 years, which is long enough to breed and continue the species.
The oldest confirmed polecat/ferret age I can find (from a wild state) is
about 6 years of age at capture.  For a long time, the life span of
polecats/ferrets in zoos and captivity was about 5-6 years, with occasional
ages reported to 10, and even one at 14, but those older ages where
exceptions until recently.  Pet ferrets have the benefit of protected lives
protected by veterinary medicine.  In the USA, the average age at death is
probably between 7-8 years.  I have heard many stories of ferrets living
until 14 years, and I have one thats 12.  Reports continue to surface of
ferrets living to 12-14, and many are true, but like reports of humans
living to 120, they are the high-end exceptions.
 
Last, unless hunting or disease pressures are present, deaths follow a
normalized distribution pattern with the mean near the mode.  It is not very
skewed, which means about as many ferrets die before 7.5 years as after.
Look at it this way; for every ferret that dies at 4.5 years of age, there
is a ferret that lives to 9 years of age.  They balance each other out in a
normal distribution.  Most deaths occur near the middle, which is why there
is a "bell" shape to the curve.
 
While I hate the term, ferrets tend to "burn out" faster than cats or dogs;
that is, they have a shorter life span reflecting their metabolic rate.  I
think it was Cuvier that remarked all mammals are granted by God the same
number of heart beats in their life, and if your heart beats 60 times or 200
times a minute, the end result is the same-- the time is just shorter.  If
it helps, just remember shooting stars burn the brightest.  To corny?  Ok,
hows this: all time is relative, and what seems to you like just a few
years, to the ferret is a lifetime.
 
Bob C and the 20 Poopmeisters from Hades
[Posted in FML issue 2159]