NANFA-- Why not to let captives go - long

Denkhaus, Robert (DenkhaR_at_Ci.Fort-Worth.TX.US)
Thu, 23 May 2002 09:41:20 -0500

I recently received my monthly newsletter from the Dallas-Fort Worth
Herpetological Society and read several interesting articles dealing with
herp conservation and ecology. Uninformed herpers, like uninformed
fishheads, often release animals into the "wild" and the real and potential
problems of the releases are virtually the same for herps and fish. I am
including the full text of the article (with permission of the author and
the DFWHS) and encourage anyone who is considering releasing fish (or any
other captive critter) to give some thought to the article.

If You Love Them - Don't Set Them Free
Michael Smith

Many of us have done it - I certainly have. So many different species, and
so little time! The answer? Get a couple of this species, one of that, a
couple of these, and pretty soon we are keeping quite a few animals. And
then it happens: that snake that was so cool when we first got it becomes
less interesting, and we begin to think about getting rid of it. What are
the options? Give it away, sell it ... or maybe just turn it loose.

"Born free, as free as the wind blows...." Well, maybe that syrupy refrain
is not echoing in our heads, but we picture our former pet gliding,
swimming, climbing, or hopping to freedom, living in the wild. Or, in a
less romanticized and more practical vein, we can tell ourselves that we
caught it at a certain location, and so why not just release it back to that

It turns out that releasing formerly captive reptiles and amphibians can
cause problems in a number of ways.

Let's start with those well-meaning folks who release individuals to try to
re-populate an area where that same species used to live. Wouldn't it be
nice if we could bring back the horned lizards or restore box turtles to the
levels we used to see? One problem is this: the original populations died
back for a reason, and unless we understand it and can correct it, the newly
released animals will probably disappear just like the original ones did.
If the habitat is still degraded (even if it looks nice it may not be able
to support the species), the released animals will die. If a changing
climate, or invading organism like the fire ant, or something else makes the
location now unsuitable, then releasing more animals will do no good.
Further, we know that in many cases relocated animals may not successfully
adapt to a new place even if the habitat is suitable.

Some people release exotic species (animals of a kind that is not native -
not found in that location), or their exotic pets may escape. One or two of
the problems with this are obvious, such as tropical species released in
temperate climates. When the weather cools, the tropical herp typically
dies because it is not adapted to the cold, and either freezes or is
weakened and becomes ill and dies. Other reasons for not releasing a
species that is not native to the area may include inability to find
suitable food or avoid local predators. The animal may be vulnerable to
pathogens (disease-causing organisms) or parasites that local species can
survive. So, releasing an exotic herp may be signing its death warrant.

An even more important worry is what may happen to the native species.
After all, the death of one pet is sad, but damaging a whole population of
local animals is far worse. A brochure from Partners in Amphibian and
Reptile Conservation (PARC) outlines some of the problems with releasing
herps that have been kept as pets or classroom displays. PARC is composed
of representatives from universities, conservation groups, federal and state
agencies, the pet industry, and others. The problems identified by PARC

* Introduction of harmful pathogens or parasites
* Increased competition with native species for resources
* Predation on native species
* Degradation of the native population's gene pool

Introduction of pathogens or parasites
One of the most well known examples of released herps introducing pathogens
into wild populations involves Upper Respiratory Tract Disease (URTD) being
spread from captive to wild tortoises in the U.S. In a 1998 update found on
the website of the California Turtle & Tortoise Club, Grace McLaughlin
provided an update regarding URTD. The disease is caused by a Mycoplasma
bacterium, is spread by direct contact between tortoises, and is difficult
to treat. Tortoises may harbor the organism in the nasal tract for years,
with recurrent symptoms appearing particularly when stressed. There have
been die-offs of desert tortoises in California attributed to people
releasing tortoises that are ill. The former pets encounter wild tortoises
and spread the disease. Gopher tortoises in Florida are also experiencing
problems with URTD, with relocated and released tortoises a possible factor.
This disease, Mycoplasmosis, has also been identified in box turtles.

Increased competition with native species
It has been interesting over the years to watch the increasing numbers of
exotic species listed in Conant & Collins' field guide. Giant ameivas,
green iguanas, and brown basilisks are among the species listed in south
Florida. These are species that are established as populations, not just a
few stray pets. But we're not just talking about tropical species
introduced to the U.S. How about our hardy and adaptable red-eared sliders
(Trachemys scripta elegans), exported around the world as pets and as food?
Released red-eared sliders have established populations in various places
around the world. They reportedly are crowding out European pond turtles.
People in the northeastern U.S. are concerned about introductions of
red-ears into ponds and marshes, thinking that they may replace some of the
local species.

Any population of a given species becomes adapted to its surroundings, and
has a particular way of functioning in those surroundings. Individuals are
adapted to eating particular kinds of things and seeking shelter in
particular kinds of places. Their behavior develops accordingly, so that
they know how to do things in certain ways. If another species is
introduced into that same location, and that other species tends to eat the
same things or use other resources in more or less the same ways, then there
is competition for those resources. The introduced animal may out-compete
the native and replace it, perhaps the native will "win" the competition, or
in some cases the competition for limited resources may weaken both species.

In other words, a population of animals is like a community in which all the
"jobs" are taken. Newcomers cannot just join the community. Maybe the
newcomer takes a little bit of everybody else's "job" (hunting their prey,
using their shelters, etc.) making everyone's existence a little shakier.
Or maybe somebody is pushed out of a job altogether and disappears.

Predation on native species
What if I breed California kingsnakes and release several clutches of babies
into the wild here in north Texas to see if I can get a population going?
If these kingsnakes survive, on what do they feed? Among other things, the
rat snakes, copperheads, massasauga rattlesnakes, and other species that we
probably enjoy and want to continue seeing. That scenario might make some
herpers think twice. And why should we be concerned only with the species
that we like? As responsible herpers and as people with at least a little
knowledge of nature, we should understand that damage to a "cool" species
like the massasauga is not worse than damage to any other equally vulnerable
animal. If our hobby was mammals we might be worrying about damage to the
northern pygmy mouse (Baiomys taylori) or some other rodent.

The bullfrog (Rana catesbiana) is an example of a species that has been
introduced into areas in the western U.S. where it has damaged other
species. Bullfrogs eat just about anything that can fit into their mouths,
and its prey list can include small snakes, other frogs, etc.

Degradation of the native population's gene pool
You've heard how some pathogens are developing antibiotic-resistant strains,
because of the overuse of certain medications. That is an example of how a
population of some organism can change genetically to adapt to new
conditions. Similarly, populations of reptiles, amphibians, and other
animals adapt to their particular situations, developing a particular
genetic makeup that is a good "fit" with their environment. For example,
west Texas ornate box turtles may have a somewhat different genetic makeup
from north Texas ornate box turtles, even though it's the same kind of
animal. If we release west Texas box turtles into a population in north
central Texas, these newcomers will bring a genetic makeup that may not be a
good fit for the environment here. As they breed with the local animals,
they change the genetic makeup of the population, possibly taking it in a
direction that will make them less successful.

So, if you have an animal that you no longer want or can no longer keep,
there are several reasons not to release it: it may die, it may expose other
animals to illness, it may compete with native animals or eat them, and it
may breed with native animals and produce babies that are less equipped for

As alternatives to releasing herps into the wild, PARC offered the following

* Give the animal to someone else
* Return it to where it was bought
* If it is a classroom display, hold it over until the next
* Donate it to a museum, science center, zoo, etc.
* Humane euthanasia

These may be good suggestions, although in most cases returning it to where
it was bought or donating it to an educational institution may not be an
option. Zoos and museums often have all the animals they can use,
especially when it comes to green iguanas and Burmese pythons! On the
other hand, sometimes you can trade or sell the animal, or if necessary talk
to a reptile rescue group about taking it. But whatever you do, please don't
turn it loose.


Conant, R., and J.T. Collins (1998) A field guide to reptiles & amphibians
of eastern and central North America (3rd Ed., expanded). Boston:
McLaughlin, G.S. (1998) Upper Respiratory Tract Disease: An Update -
January 1998. California Turtle & Tortoise Club website:
PARC (2002) Please ... Don't turn it loose! (brochure available at the
PARC website: <>
University of Florida. (2002) Mycoplasmosis of tortoises. University of
Florida Small Animal Clinical Sciences website:

Rob Denkhaus
Fort Worth Nature Center & Refuge
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