by Bob Church
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 degradation, 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 recognised 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 spheroid 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 insulinoma (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 that's 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 normalised 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. Too corny? OK, how's this: all time is relative, and what seems to you like just a few years, to the ferret is a lifetime.