Q:"You wrote alot about ferrets being like weasels. Can you be more
   specific?"
 
A: Sure, ferrets are VERY MUCH like weasels because they ARE weasels.
   Specific enough?
 
The natural history of ferrets is extremely similar to all other members of
the _Mustela_ genus, with just a few exceptions relating to domestication
and/or niche specialization.  These traits show a close relationship which
allows us to use one to act as a model for other members of the group.  It
doesn't always work, especially with traits modified by selective breeding
during domestication, but as a rule the method is generally sound and
commonly used.  Since space is limited, I shall pointed out a few
reproductive traits:
 
AGE AT SEXUAL MATURITY: MALE:
1 year = Long-tailed Weasel, Short-tailed Weasel (or ermine), Ferret,
European Polecat, Black-footed Ferret, and European Mink.
9-10 months = American Mink, Steppe Polecat.
3-4 months = Least Weasel.
 
AGE AT SEXUAL MATURITY: FEMALE: 1 year = Ferret, E. Polecat, BF Ferret,
and E. Mink.
9-10 months = A. Mink, S. Polecat.
3-4 months = L. Weasel, LT Weasel, ST Weasel.
 
INDUCED OVULATION: LT Weasel, ST Weasel, Ferret, E. Polecat, BF Ferret, E.
Mink, A. Mink, S. Polecat, L. Weasel.
 
DELAYED IMPLANTATION: LT Weasel, ST Weasel, A. Mink, L. Weasel.
 
AVERAGE LITTER SIZE:
3-4 = BF Ferret.
4-5 = E. Mink, A. Mink.
5-6 = L. Weasel.
6-7 = LT Weasel, ST Weasel, E. Polecat.
6-9 = Ferret, S. Polecat.
 
LITTERS BORN PER YEAR: 1 = LT Weasel, ST Weasel, E. Polecat, BF Ferret, E.
Mink, A. Mink, S. Polecat.
2 = Ferret, L. Weasel.
 
AVERAGE REPRODUCTIVE LIFE SPAN:
2-4 years = Ferret.
3-4 years = L. Weasel.
4-5 years = E. Polecat.
5-6 years = LT Weasel, ST Weasel.
6+ years = S. Polecat, E. Mink, A. Mink.
 
JUVENILE SEX RATIO: 1:1 = LT Weasel, ST Weasel, Ferret, E. Polecat, BF
Ferret, E. Mink, A. Mink, S. Polecat, L. Weasel.
 
PHOTOPERIOD-REGULATED REPRODUCTIVE CYCLES: LT Weasel, ST Weasel, Ferret, E.
Polecat, BF Ferret, E. Mink, A. Mink, S. Polecat, L. Weasel.
 
Here are a few bonus categories thrown in:
 
PRIMARY (OBLIGATE) CARNIVORES: LT Weasel, ST Weasel, Ferret, E. Polecat,
BF Ferret, E. Mink, A. Mink, S. Polecat, L. Weasel.
 
EXCLUSIONARY SEXUAL TERRITORIALISTS: LT Weasel, ST Weasel, Ferret, E.
Polecat, BF Ferret, E. Mink, A. Mink, S. Polecat, L. Weasel.  (The ferret
can be gregarious when artifically housed as a pet).
 
CACHING BEHAVIOR: LT Weasel, ST Weasel, Ferret, E. Polecat, BF Ferret, E.
Mink, A. Mink, S. Polecat, L. Weasel.
 
OLFACTORY IMPRINTING:
CONFIRMED: LT Weasel, ST Weasel, Ferret, E. Polecat, BF Ferret, E. Mink,
A. Mink, S. Polecat,
UNKNOWN: L. Weasel.
 
EASILY TAMED TO AT LEAST ONE PERSON: LT Weasel, ST Weasel, Ferret, E.
Polecat, BF Ferret, E. Mink, A. Mink, S. Polecat, L. Weasel.
 
PREY KILLED BY BITE TO BASE OF HEAD/NECK: LT Weasel, ST Weasel, Ferret, E.
Polecat, BF Ferret, E. Mink, A. Mink, S. Polecat, L. Weasel.
 
With weasels, the important things are not so much the similarities as the
differences.  Nearly all the differences, such as body size, prey animals,
activity periods, etc., are all related to the exact niche the animal is
exploiting.  This has a tremendous bearing on questions of the domesticated
ferret being able to do the New Zealand thing and form feral populations.
Assuming the ferret would fill the same niche as the European Polecat, can
it find a spot in North America to form colonies?
 
The answer is no, and for a very simple reason.  Because all mustelids
are similar in niche requirements, when they overlap with other types of
mustelids, they "partition" the niche; that is, they narrow their choices
to allow room for all to coexist.  This has lots of effects, but four
important ones are 1) they "stair-step" their body size so to exploit a
slightly different mix of prey animals; 2) they vary their activity periods
so not all will be active at the same time; 3) they exclude all other
members of their same sex and species; and 4) there are fewer numbers of
each type of mustelid making the predator mass approximately the same.  In
other words, if the environment will only support 12 predators, you can't
have 13.  Adding new species only reduces the other species' populations.
 
Now, probably the primary reason ferrets haven't gone feral in North
America, even though being here for two centuries, is because there is
no room at the inn.  In Europe, mustelids dovetail quite nicely in the
following pattern: European mink, American mink, European polecat/ferret,
ermine, common weasel.  The American mink has forced itself between the
European mink and the polecat, taking parts of both animal's niches.  In
North America, the dovetailing is even tighter: least weasel, ermine,
long-tailed weasel, American mink.  In areas where the black-footed ferret
used to live, mink were uncommon.  Now, for the ferret to go feral, it
would have to steal parts of the niche from the long-tailed weasel and the
mink, both of which are superb generalist predators, well established, and
not only any endangered list.  Since the American mink has been successful
in stealing parts of niches from the European polecat--a far better
predator than it's domesticated cousin--it is more than doubtful that the
ferret could do better on the weasel's and mink's home ground.  Even if you
think it is possible, you still can't discount history; in more than 200
years, ferrets have never been able to establish sustained feral colonies
in North America despite numerous intentional and accidental releases.  All
die out.
 
Bob C and 20 Mo' Stair-Steppers
[Posted in FML issue 2529]