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NONLETHAL CONTROL OPTIONS FOR PREDATION
MANAGEMENT ON WILDLIFE
WILLIAM F. EDMISTON
, D.V.M., Sheep and Goat Predator Management Board, P.O.
Box 3543, San Angelo, Texas 76902; e-mail email@example.com
, Department of Wildlife and Fisheries Sciences and Texas Agricultural
Extension Service, 7887 U.S. Highway 87 North, San Angelo, Texas 76901-9714; e-mail
: Changing mores about predators and their management over the last thirty years
have prompted the need for nonlethal approaches to predator management. Considerable
effort since that time regarding cultural practices (e.g., shed-lambing), fencing, and guarding
animals have provided management alternatives for livestock producers who suffer losses
from predators. However these alternatives may not be applicable or effective when
attempting to minimize wildlife losses to predators. We discuss (a) current efforts on the use
of immunocontraceptives as a means of reducing coyote (Canis latrans
) populations, and (b)
general guidelines for habitat management as a means of dissipating predator-induced
mortality on upland game birds and deer (Odocoileus
WHY LETHAL CONTROLS?
depredation by raccoons (Procyon lotor
Further, tools like the Livestock Protection
Collar offer control for the specific coyotes
that are causing livestock damage, but such
expanding human population, changing land
remedy for excessive predation on big game
environments, and changes in the sheep and
goat industry in Texas have increased the
approaches to predation management. Inthis paper we discuss some new and old
approaches to reducing predation losses todeer (Odocoileus
spp.) and quail (Colinus
and Callipepla squamata
a series of approaches aimed at inducingcontraception or sterility in coyotes. The
basic concept of immunocontraception is to
control to protect wildlife has some inherent
differences than that designed to protect
process (DeLiberto et al. 1998). Research,
funded in part by Sheep and Goat Predator
affecting wildlife populations, e.g., nest
National Wildlife Research Center Predator
higher dose is effective, or if coyotes use a
Millville, Utah and Utah State University
different biological pathway not affected by
since 1995 to test immunocontraceptives in
coyotes. Lethal techniques to resolvelivestock-predator conflicts are becoming
less acceptable to the public due to changing
social values, and this research can assist in
means for pregnancy termination in coyotes.
Bromcriptine, although structurally similar
situation. This research was undertaken with
to cabergoline, differs in its affinity for
socially-acceptable and environmentally-safe alternative to lethal control techniques.
should be deliverable by an oral route, such
as the method used for oral rabies bait drop,
appear to have potential usefulness only on
studies are undertaken based on the premise
that provisioning of pups is a key factor in
constraints of contraception based on time
established territories (Bromley 2000). Thisbehavior often results in coyotes located on
one ranch where they are acceptable to land
adjacent properties, with resulting wildlife-
luteinizing hormone (LH) and folliclestimulating hormone (FSH) producing cells
of the anterior pituitary gland. Damage to
identified to reduce fertility in coyotes. It is
sterility of both sexes, perhaps permanently.
pregancy in dogs, and patent rights willsoon lapse on this drug. Research at NWRC
the last two years was unable to document
pregnancy. Recent work in Australia in red
initiate development of an orally-deliverable
currently underway to determine whether a
studies are directed at the development of a
safe, legal, and ethical population control
raccoons. However, Ratnaswamy et al.
(1997) used the same estrogen compoundand failed to demonstrate a CTA of
CONDITIONED TASTE AVERSION
raccoons for reducing depredation of eggsof sea turtles.
nest depredation may be conditioned taste
effectiveness of lithium chloride-treated
which animals associate the taste of a food
consumption. The predators show that they
were equivocal; one study site demonstrated
have acquired this learning or, conditioning,
a successful CTA and the other did not.
offending food wherever it is encountered
refinements with dosage, and perhaps other
long after they have fully recovered from
chemicals, may have provided better results.
Also, the mesomammal community wascomplex at Hernandez’ study sites, and thus
directed at providing a nonlethal means of
(Gustavson et al. 1974, Ellins et al. 1977).
Results have been mixed (Burns 1980,
Nicolaus (2000) provide a review of various
CTA trials to reduce livestock predation and
the biology of how CTAs are developed and
implemented. Similarly, Conover (1989)and Nicolaus (1987) provide reviews of
(a) predators need to be of relatively small
using CTA for reducing egg depredation by
(b) predators need to occupy small,overlapping home ranges;
rather simple, i.e. low species diversity;
(d) the are to be treated needs to be rather
Nicolaus 1982, Conover 1989). Of theaversive chemicals tested, emetine
hydrochloride appears to be one of the mostpromising, but emetine is hazardous to use
and thus it’s potential for field applications
is limited (Conover 1989, 1990). Semel and
prickly pear, especially if conventional grass
preferred and the bottom of the fence should
microhabitats are limited (Slater et al.
Sometimes modifications to the fence, e.g.,a buried net-wire “apron”, or an offset
electric tripwire (or 2) spaced about 6 inches
outside the fence and about 10 inches high,
suitable nesting clumps per acre. A suitable
nest clump will be about the diameter of a
effectiveness. Fences are not generally not
basketball and at least 18 inches in height.
effective deterrents for foxes, bobcats, and
raccoons because of their tendency to climb
13 feet. Slater et al. (2001) reinforced this
threshold when they found that simulatednests placed in prickly pear had no higher
survival than grass nests at sites thatfeatured at least 300 grass clumps per acre.
minimizing predation management on one’s
prickly pear survived higher than those in
target species of wildlife is to tailor the
nest sites. Slater et al.’s data suggest that
habitat in such a way that it facilitates the
the best offense against nest predators is a
prey’s needs more than the predator’s. This
maxim is easy to comprehend and visualize,
opportunity to nest at a number of locations
but more difficult to quantify. Generally
predators’ ability to locate the nest. Anyone
provide a greater quantity of suitable habitat
who has ever played a “shell game” can
relate to how such laws of chance operate.
The more “shells” the better the odds that
the “dealer” (in this case the quail) will win.
predators’ search efficiency is diluted, and
Conversely, as the number of grass clumps
diminishes, it only enhances the predator’s
odds of locating a nest. The latter situationis currently a topical problem in quail
success is typically “low”, e.g., less than 30
, this volume). Bobwhites tend to
nest in past-year’s growth of a bunchgrass
s u r r o u n d i n g s w e r e “ l a r g e l y
like little bluestem (Schizachyrium
indistinguishable”, but only 28% for nests
; Guthery 1986, Lehmann 1984).
situated in clumps of grass conspicuously
Scaled quail in Pecos County nested almost
better than their immediate surroundings.
entirely in tobosa (Hilaria mutica
; Buntyn et
Buntyn et al. (2000) reported nest success
al. 2000). Both species will also nest in
1999 nesting season. This high success rate
exemplifies Lehmann’s observation about
using a “softball model” for assessing
recommended that suitable loafing coverts,
e.g., lotebush (Ziziphus
sp.), be spaced nomore than a softball-throw apart (ca. 150
feet). For proper nesting habitat, a softball
on several fronts relative to ranching, we
tossed pitching distance (46 feet) should not
believe it does provide an important nesting
be visible to the thrower. Such conditions
substrate for quail, and especially in drought
will be satisfied by bunchgrass densities of
Plains is currently (i.e., nesting season of
inches in height or in fairly dense tobosa
microhabitat if not for prickly pear. Whilewe can offer no specific recommendations
of prickly pear density for quail nesting, a“good” mix of prickly pear and perennial
grasses seems to provide a quality nesting
coyotes, especially until they are about eight
weeks of age. Although coyote predationon fawns can be a management constraint in
some areas of Texas, comparable thresholds
rehabilitating nesting cover. Good grazing
for delineating good fawning habitat are not
management which may entail rest, reduced
“some is good and more is better” (R.
rotational schemes should be incorporated
to promote a higher range condition, i.e.,
Department, personal communication).
typically the taller-growing bunchgrasses
Generally areas of taller grasses, e.g., higher
range condition or ungrazed blocks ofConservation Reserve Program pastures, are
need generic “escape cover” which includes
herbaceous cover (i.e., grass), screeningcover (e.g., low brush and broomweed), and
escape cover which may include some areas
brush control. Rollins (1983) reported that
Ashe juniper (Juniperus asheii
). Such sites
may be important until grass cover increases
describe the “cone of vulnerability” of quail
to suitable levels to provide protection for
vulnerability” for threats from ground-
individual trees into brush piles, and their
subsequent burning, may be undesirable for
parameters relate to brush and herbaceous
DeLiberto, T. J., E. M. Gese, F. F.
Knowlton, J. R. Mason, M. R. Conover, L.
Bromley, C. 2000. Coyote sterilization as
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