Krystal,
 
1.  Since most ferrets sold as pets are neutered/spayed, I'd find their
ability to establish feral colonies somewhat limited at best <G>.
 
2.  If you can find a copy of "1990 Public Information Manual" published by
the California Domestic Ferret  Association, you will find copies of letters
from the Depts of Interior/Wildlife of all 50 states, stating that there are
no feral colonies of the Domestic Ferret in their state.  Remember that
ferrets have been in this country since the late 1600's, and until this
century most of these ferrets were unaltered and capable of breeding.  If
they were capable of establishing breeding colonies, they would have by now.
 
3.  There were attempts to establish colonies of "wild" ferrets on an island
off the coast of  Washington that was overrun by European rabbits.  The
attempt was unsuccessful.  There are no feral ferrets there now.
 
4. Dr. Fitzgerald of the Univ of Iowa concludes that to be successful in
'invading' an ecology, "the invading species need to be long lived, have a
shorter  generation time, be fairly impervious to predation.  The ferret, she
found,  was short lived, extremely subject to predation, had a long
generation time compared to the native weasel and  [is] a less efficient
predator than any weasel found in  the U.S."  She concluded that  "the fear
of drastic ecological impact from the keeping of these animals in North
America is an unwarranted speculation." [Fitzgerald, V.J. "The domestic
ferret as a threat to wildlife"; The Ferret 2(3):2-4 1988; Phillips, W. and
Shimbo, F., "1990 Public Information Manual"; CDFA, 1990]
 
Hope this helps.
 
Dick Bossart
[Posted in FML issue 1138]