PLEASE, I retain all rights and request this be considered a "preliminary
draft only: do not cite, redistribute nor duplicate without permission of
the author" version.
[Posted in two parts, combined here into one... BIG]
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Ten Reasons Ferrets Cannot Go Feral In California (Actual working title:
The California Ferret Issue: Putting the "Con" into Controversy).
Olfactory Imprinting.
The crux of the CDFG argument for excluding domesticated ferrets from
California is that they constitute a grave danger to native fauna and
livestock. The CDFG suggests that because the domesticated ferret (Mustela
furo) is so closely related to the polecat progenitor (M. putorius, M.
eversmannii, or hybrids), that they maintain a similar set of genetic
behaviors, or instincts, which enable them to revert from a pet to a
predator upon introduction into the wild. In both implicit and implied
statements, the CDFG maintains the domesticated ferret has behavioral
instincts which would enable it to easily naturalize, causing severe impact
to native species. This is the foundation of the CDFG argument; if ferrets
were not a danger to the native fauna and livestock of California, then
there would be no reason to exclude them from the state. Because of the
extreme importance of this point, the CDFG emphasizes it above all else.
It is, perhaps, a primary reason why the Sierra Club and Audubon Society
has joined the CDFG to support ferret exclusion.
Put simply, if pet ferrets did not present a clear danger to the wildlife
and livestock in California, there would be no reason to make possession
illegal. This danger is postulated by the CDFG in several arenas; by
direct predation of threatened or endangered animals, by direct and
indirect competition with native predators, and by the potential loss of
native diversity and species richness (a byproduct of the two preceding
reasons). This position is supported by events in New Zealand, to be later
discussed at length, where feral ferrets introduced during the late 19th
and most of the 20th Century have contributed to some unquantified degree
to the decline of several avian species, as well as the possible extinction
of others. As the argument goes, if it could happen there, it could happen
in California.
Although on the surface this argument appears to be well supported by the
New Zealand example, is in fact obtuse and misleading because it assumes
similar conditions between the two populations, including breeding, kit
rearing and local environments. In other words, if one population is to be
used as a homologue for naturalization for the other, then they must have
similarities beyond those of species; they need to have similar modes of
life. One of the most profound differences (but certainly not the only
difference as will be apparent later) between the pet ferret population v.
New Zealand feral ferrets is the difference in olfactory imprinting.
It has long been demonstrated that members of the polecat group, Putorius
(which includes the domesticated ferret), olfactory imprint on prey scents
during the weaning and early juvenile stages of life. In the first six
months of a domesticated ferret's life, the smells of the foods it will
consume for the remainder of that existence are so strongly imprinted in
the ferret's brain structure that they have been known to die of starvation
rather than sample unrecognized food. Most pet ferret owners are
intimately aware of this and take great pains to expose kits to as wide a
food choice as possible to help prevent future problems associated with
olfactory imprinting. At least one ferret breeder recognizes this as well,
feeding weaned kits a food product they market separately. When the kits
are purchased, they will show a decided preference for the breeder's
product, prompting pet owners to continue to buy the food. Studies have
shown the imprinting process begins during suckling, so even the specific
diet of the mother can influence the olfactory imprinting in the ferret.
Perhaps the most basic requirement for predation is recognition of prey.
Domesticated ferrets, like cats, respond to objects moving at specific
speeds and directions across their field of vision; pet ferret owners
frequently exploit this trait during play. In this regard, domesticated
ferrets are little different from other carnivores. However, unlike most
carnivores, polecats (and by extension, domesticated ferrets) are not
primarily visually oriented. Extremely myopic, members of the polecat
group use smell as their primary sense to locate potential prey, homing in
on the scent rather than the sight of the animal (sight is used, but only
after prey have been located and in close range). This is also well known
by pet ferret owners; blind ferrets can often navigate their environments
as well as sighted ferrets, making identification of visual problems
difficult. Because the ferret imprints on smell, rather than vision, it
only eats those animals with odors recognized as food. Domesticated ferret
owners have reported this as well; in the attempt to provide a more natural
diet for their pets, some owners will provide a mouse as a diet supplement.
If alive, the mouse may trigger typical carnivore hunting reactions, but
once dead, the mouse frequently becomes little more than a plaything. Even
though Old World mice are typically found on lists of polecat prey items,
the mouse will not be typically recognized as food, and is usually
abandoned or cached, uneaten.
How can this occur when feral ferrets clearly capture, kill and consume
live prey, a phenomenon mirrored by European working ferrets? Indeed, the
probable reason for domestication of polecats was so they could be used as
mousers. The reason is because domesticated ferrets, kept as pets in the
U.S.A., are primarily fed kibbled or extruded dry foods their entire life.
These foods are composed of a large amount of plant starches and rendered
protein and fats, and smell more like bread than prey animals. There are
many reports of ferrets readily accepting grain based foods, such as breads
or pastries, yet ignoring chunks of chicken or beef. What this means is,
lost or abandoned pet ferrets only have a short window of survivability in
the wild; few domesticated ferrets, imprinted on cat or ferret foods,
survive more than a few days. If they can escape predation, they usually
starve. In most cases where ferrets have been recovered after a long
period of time, they have usually been shown to have survived by consuming
dog or cat foods left out for pets, human garbage that included grain-based
foods, or are in an extremely malnourished state when recovered. This type
of response is typical of mustelids; attempts to introduce native black
footed ferrets (a wild relative of the domesticated ferret) were hampered
by a lack of olfactory recognition
Compare this to the New Zealand ferrets, introduced more than a century
ago, who were well imprinted on rabbits, rats and mice PRIOR to release;
these being a primary source of food for them as working animals. Thus,
it would appear at an extremely superficial level that pet ferrets, being
essentially from the same ancestral stock as the New Zealand feral ferret,
could follow the same pattern of naturalization. However, in truth,
there is very little comparison between the two in regards to olfactory
imprinting, which makes direct comparisons impossible. In other words,
because the conditions between the two populations are so different, they
cannot be considered homologues. Any comparisons between the two are
inherently flawed because the conditions of introduction are so vastly
different.
Olfactory imprinting is not precise; predictive statements are
generalizations made at the population level, so individual ferrets may
display more or less of an ability to accept new foods. A window of
opportunity is created when the ferret is introduced into the wild, which
extends to the point of death from malnutrition or associated disease. If
the ferret cannot learn to recognize the new food during that time period,
it will simply die. If it learns to recognize new food, but only after an
extended period of time which has depleted body reserves, it is simply too
late and the ferret dies of starvation or related disease. Only those
extremely rare ferrets able to ignore olfactory imprinting have the chance
to take advantage of the window of opportunity and survive.
When introducing exotic mammals, numbers are everything; the smaller the
introduced population, the more unlikely it will naturalize. Even if 5%
of all ferrets can take advantage of that window of opportunity and ignore
their olfactory imprinting, given the size and breadth of California and
the degree of urbanization, a ferret would have to overcome astronomical
odds to be able to form a viable breeding population. By itself, the odds
aren't too bad and the CDFG may have a point in their favor. However,
ferrets are not controlled by abstract checklists where possibilities take
on a reality not expressed in living populations. The competent scientist
MUST look at ALL factors involved. As you will see, as each factor is
explored, the possibilities become more and more remote. There are reasons
ferrets went feral on New Zealand and established a large breeding colony,
but in two centuries have not created feral populations in the United
States. Olfactory imprinting is one of them.
Next: Predatory Skills
Bob C and 15 MO' Polecat Posse Pharts
[Posted in FML issue 3165]
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