Killing Natural Predators Does Little Good
-Dave Rice, Reno Gazette Journal, February 9, 2007
"And to the conservation biologist, it is an embarrassing contradiction between science
That's the opinion of wildlife managers regarding the killing of 100,000 native U.S.
predators each year by the Wildlife Services branch of U.S. Department of Agriculture,
according to William Stolzenburg, a freelance journalist.
"Topping the casualties are some 70,000 coyotes," he said in a recent article.
Given to me by my friend and former wildlife manager, Fred Wright, the article was
the feature article, "US or THEM," in the Oct.-Dec. 2006 edition of the magazine
"Conservation In Practice," published by the Society for Conservation Biology. In
the article, Stolzenburg takes a fresh look at why predators not only continue to
be killed in America, but why the archaic practice seems to be gaining more of a
following in recent times, despite scientific studies that conclude that it is unnecessary
and does little good.
At the heart of Wildlife Service's work on predator control is a $10 million budget
mainly used on its coyote control program, which kills approximately 75,000 of the
wild dogs to reduce predation on domestic sheep in the western U.S. Stolzenburg cites
a study conducted 10 years ago by Kim Berger, then a master's student at the University
of Nevada, Reno, that the significant decrease of the domestic sheep in the west
(85 percent since the 1940s) was not due to coyote predation, as often claimed by
sheepmen, but was mainly due to economic reasons.
"It turns out the biggest culprit by far to explain the missing sheep is the high
price of hay. Wages and lamb prices are important players, too," Stolzenburg wrote
in his article. "Even the rancher's age has more to do with his predicament than
do predators. At the statistical bottom of Berger's list of prime suspects sits the
Stolzenburg concedes that certain predators in certain situations can make life miserable
for those struggling to make an honest living raising what he refers to as easy prey.
"Whereas modern biologists would often recommend surgical tweezers in that regard,
the nostalgic tool of choice for those in charge remains the sledge hammer: kill
enough coyotes -- or bears or wolves or cougars, goes the thinking -- and the problem
will be solved."
That same line of flawed reasoning exists here in our state also. For many years,
a small but tenacious and vocal group of Nevada hunters have attended Wildlife Commission
meetings and encouraged commissioners to do something about predators, mainly mountain
lions, in the state that they claim were killing vast numbers of deer each year,
and to a lesser extent, bighorn sheep. Deer numbers have been down for more than
a decade and the reasoning of those who blame mountain lions is simple: kill mountain
lions and the deer herds will return. Some individuals even contend -- and apparently
believe since they are quick to repeat their theory -- that every mountain lion in
the state kills a deer a week.
Using a figure of 3,000 lions statewide, a reasonable figure according to NDOW, the
annual predation level by lions reaches 150,000 deer per year, which would roughly
double the state's population of this species in a good year. The problem with the
outlandish theory is that each mountain lion does not kill a deer a week.
Another interesting point made by Stolzenburg was a finding made by three scientists
at California's Hopland Research and Extension Center. The key and consistent point
coming out of Hopland was that not all coyotes kill sheep, according to study results.
The Hopland researchers learned through 14 years of radio tracking and DNA testing
that nearly every sheep killed by a coyote is killed by an alpha coyote. Since alpha
coyotes are the savviest and most suspicious of the clan, they are the most difficult
The conclusion of the Hopland group was, "...that randomly slaughtering a bunch of
coyotes to protect a flock of sheep was as effective as killing no coyotes at all,"
according to Stolzenburg.
A very interesting point made by Stolzenburg in his article is that when predator
populations are significantly reduced, populations of their prey grow unchecked and
often negatively affect their habitat and the habitat of other species. He cites
many examples from white tailed deer numbers in the east growing beyond their carrying
capacity because of the lack of predation, to the fall of kelp forests where sea
otter numbers were insufficient to keep kelp-eating sea urchins in balance.
Another intriguing example is the re-establishment of gray wolves in Yellowstone
"For the last decade, packs of gray wolves have run loose in Yellowstone National
Park," Stolzenburg wrote. "Their presence has apparently transformed the land's living
fabric. For the previous 70 years, willows had been chewed to stubs by the world's
largest herd of elk. Now, with wolves patrolling the stream valleys, willows have
suddenly and conspicuously sprouted into thickets two meters tall."
The growth of the willows has been good for other types of wildlife including beavers,
songbirds, salamanders, trout and muskrat. In addition, the numerous elk carcasses
have become important to scavengers; 12 species in all.
Early Nevada newspapers often reported in the late 1800s of rancher and farmer problems
with what they felt were an overabundance of predators that they tied to losses of
cattle, sheep and other domestic animals. Shortly after significant and apparently
successful programs to kill these predators, these same farmers and ranchers were
besieged with huge numbers of herbivores including rabbits, squirrels, gophers, marmots,
and other plant eaters that attacked and ruined their crops. There were few if any
predators left to keep these populations in check.
Stolzenburg concludes that fear and aggression in humans are offset, at least in
part, by curiosity and reverence towards animals.
"Long ago these were traits that helped the human animal learn the art of survival,
if not the grace of sportsmanship, from its most dangerous competitors," he wrote.
"And so these traits remain, manifested as the inner magnets that bring world travelers
to Serengeti lion safaris and throngs of wolf-watchers to Yellowstone's Lamar Valley.
Therein may be reason to believe the human capacity to live with predators may one
day overhaul its overwrought habit of killing them."
Effects of Coyote Control on Domestic Sheep and Game Animals Robert
L. Crabtree, for Predator Defense Institute, Nov., 1997 (Crabtree is a wildlife ecologist
who has studied coyote behavior extensively in the West.)
Dear Interested Person or Party:
The following is a scientific opinion letter that has been requested of me by the
Predator Defense Institute. This letter outlines a response to the general question
"What effect does reduction of coyotes (older than 6 months) have on the remaining
population?" Several opinion requests were made to me regarding claims that reduction
of adult coyotes would lessen predation on domestic sheep or game animals such as
mule deer or antelope.
Before I cover the three basic biological responses by coyote populations to reduction
(described below), it is important to understand the type of "predator reduction"
or "coyote control" in question. Most reduction programs, often referred to as control
practices, are indiscriminate in nature, meaning the individuals removed (this usually
always means "killed") are probably not the offending individuals. Even if some offending
individuals are removed, there is great likelihood that the responses described below
will take place anyway. Although removal of offending individuals can temporarily
alleviate predation rates on the protected species, the alleviation is usually short-term
and likely has long-term side-effects that make control activities ineffective. It
can not be over-emphasized how powerfully coyote populations compensate for population
reductions. Both evolutionary biology and the results of my research the last three
years (on the effects of wolves on coyotes) indicate that the basis of this resiliency
is embedded in the evolutionary past of the coyote. Coyotes evolved, and learned
to coexist, in the presence of gray wolves--a dominant competitor and natural predator.
The following demographic responses are based on published research, results of preliminary
analysis of coyote study populations subjected to various levels of reduction or
exploitation, and the work I have conducted in three study areas over the past 14
years in Washington (an unexploited population, not subject to human control or mortality),
California (exploited), and Wyoming (unexploited). There is little, if any, scientific
basis for control (reduction) programs that indiscriminately target adult coyotes.
In fact, the mechanisms described below suggest that widespread control (even selective
control) increases immigration, reproduction, and survival of remaining coyotes.
It has been reported that sustained reduction of coyote numbers can only be accomplished
if over 70% of the individuals are removed on a sustained basis. My experience with
known populations indicates that even with intensive control efforts, this level
is rarely achieved.
(1) Actual reduction in the density (and number of coyotes) does occur but is compensated
by immediate immigration into the reduction area by lone animals or shifts in surrounding
social groups. This is the expected response by species that are territorial and
monogamous. The primary objective for loners or replacement coyotes is to find a
temporal opening, defend and exploit the food resources in that social group, pair-bond
(2) Reduction results in a smaller social group size which increases the food per
coyote ratio. This ratio may be even greater because of temporary reductions in overall
density. Therefore, this food surplus is biologically transformed into higher litter
sizes and higher litter survival rates. Review of literature indicates that the increase
in litter size at birth is not as great as was previously reported by F Knowlton
in 1972. Rather, the increase in food availability improves the nutritional condition
of breeding females which translates in higher pup birth weights and higher pup survival.
(3) Reduction causing higher pup survival is fundamentally a function of the general
mammalian reproductive strategy that delays the majority of reproductive energetic
investment beyond the gestation period, the post-partum and neonate state ( e.g.,
young pups). The caloric demand of offspring reaches an apex in May, June, and July
when coyote pups grow very fast. Thus, the normal litter of six pups has a good chance
of (a.) surviving the typically high summer mortality period and, (b.) being recruited
into the pack the following winter as adults. By contrast, in the two unexploited
populations I investigated, the average litter size at birth was 5 or 6, but due
to high summer mortality, only an average of 1.5 to 2.5 pups survive. In populations
subjected to less than 70% removal annually, there appears to be an ample number
of breeding pairs to occupy all available territory openings and litter sizes of
6 to 8 enjoy high survival rates (most pups born survive to adulthood). This results
is a tripling of the number of hungry pups that need to be fed. "Large packages"
of prey, (such as sheep, as opposed to voles or rabbits,) make for more efficient
sources of nutrition because hunting adults have to invest less energy per unit of
food obtained. ADC-funded research clearly indicates that the primary motivation
to kill domestic sheep is to provide food for fast-growing pups.
(4) Reductions of adult-sized coyotes 6 months or older, results in smaller pack
size which leaves fewer adults to feed pups. This may further add incentive for the
remaining adults to kill larger prey as well as putting pressure on the adults to
select for the most vulnerable prey venture close to areas of human activity. Because
predators like coyotes also learn what is appropriate food when they are pups, and
are reluctant to try ‘new’ food sources unless under great stress (such as having
to feed a large litter of pups) reduction programs, in effect, may be seen as forcing
coyotes to try new behaviors (eating domestic livestock) which they would otherwise
avoid. Research has clearly shown that higher numbers of adult pack members provide
more den-guarding time and more food brought to pups. Without pressure to "maximize"
efficiency in hunting for food for pups, packs may be able to subsist on larger numbers
of smaller prey (e.g., rabbits and small rodents) rather than going for livestock
or other, larger prey like antelope and mule deer fawns.
(5) Reductions cause an increase in the percentage of females breeding. Coyote populations
are distinctly structured in non-overlapping but contiguous territorial packs. Over
95% of the time only one female (the dominant, or "alpha") breeds. Other females,
physiologically capable of breeding, are "behaviorally sterile". Exploitation rates
of 70% or higher have to be imposed in order to decrease the number of females breeding
in a given area. Either a subordinate female pack member, or an outside, lone female
can be quickly recruited to become an alpha or breeding female. My research has shown
that light to moderate levels of reduction can cause a slight increase in the number
of territories, and hence the number of females breeding.
(6) Reduction causes the coyote population structure to be maintained in a colonizing
state. For example, the average age of a breeding adult in an unexploited population
is 4 years old. By age 6 reproduction declines, whereby older, alpha pairs maintain
territories but fail to reproduce. This may eliminate the need to kill sheep or fawns
in the early summer in order to feed pups. Exploiting or consistently reducing coyote
populations keeps the age structure skewed to the young (average age of an alpha
is 1 or 2 years) and in a state of constant social and spatial flux. Therefore, the
natural limitations seen in older-aged, unexploited populations are absent and the
territorial, younger populations are much more productive.
(7) Reductions cause young adults (otherwise prone to dispersing) to stay and secure
breeding positions in the exploited area. This phenomenon is well-documented. There
are other demographic responses that negate the effectiveness of control practices
but the aforementioned covers the most important.
An aspect of coyote predation on livestock that is often overlooked is the availability
or dearth, of alternate prey. ADC research has demonstrated that coyotes will avoid
novel prey, such as domestic livestock. In addition, it is risky for coyotes to predate
upon domestic livestock because of human control actions associated with this behavior.
Related research indicates that predators switch to alternative prey when a preferred
prey item is absent or in low numbers. Voles and other rodents like jackrabbits are
a preferred major staple of coyotes in the West. These prey species require cover
and ample supplies of forage (grass and forbs). On many western rangelands grasses,
forbs, and protective cover have been greatly reduced by domestic livestock grazing,
leaving predators with fewer preferred prey to utilize. Present or historic grazing
impacts should be assessed as a likely means of predicting overall predation rates
on other prey species, especially prey like domestic sheep which are already vulnerable
to predators due to their lack of anti-predator behaviors.
Accelerated selection pressures and learned behaviors
A relatively unexplored, but promising avenue of research is the long-term genetic
and behavioral changes in coyote populations subjected to decades of exploitation.
It seems obvious that the type of selection pressures and selection rates have been
greatly changed for coyote populations, after a century of exploitation at 20% to
70% per year. More nocturnal, more wary, more productive, more resilient individuals
have probably been intensively selected for. This in turn may cause coyote populations
to resist control practices that previously were effective. In addition, the possibility
of social facilitation and learning may be altered or reduced. Coyotes, like many
mammals, learn to habitually use certain prey or habitats from other individuals
in the population, especially from older adults in their social group (if they have
one). Coyotes, already a highly social and adaptable species, are held in a younger
colonizing state when they are exploited and learned or traditional behaviors may
be lost. Individuals are therefore more susceptible to learning novel prey sources
or trying out novel habitat types. There are many questions to be answered such as,
"How will coyote populations respond once predator reduction or control programs
are terminated?" or "Are there other management alternatives, both lethal and non-lethal,
that may be effective in reducing predation on domestic livestock?" However, this
scientific opinion only addresses a narrow, but important topic of the impacts of
human caused reduction of coyote demographic parameters. In conclusion, the common
practice of reducing adult coyote populations on western rangelands is most likely
ineffective and may even increase the number of lambs, fawns, and calves killed by
coyotes. Coyotes are still products of their evolutionary past. Biological and ecological
evaluation of control practices would seem to be a requirement for any public or
private effort to reduce losses due to coyotes or any other predator.
Predator Control Fails to Help Sheep Industry
Wildlife Conservation Society
March 15, 2006
Decades of U.S. government-subsidized predator control has failed to
prevent a long-term decline in the sheep industry, according to a
study by the Wildlife Conservation Society (WCS), which says that
market forces – not predators – are responsible for the drop-off in
The study, which appears in the latest issue of the journal
Conservation Biology, says that more than 80 years of federally
subsidized predator control with a total investment of more than 1.6
billion dollars have not been able to stave off an 85 percent decline
in the sheep industry since its peak of 56.2 million animals in 1942.
According to the study, predation by coyotes is often cited as the
primary cause of the decline. However, 80 years of historical data
reveal that a variety of market trends ranging from fluctuating hay
prices and rising wages for livestock workers, to the drop in
wholesale prices of lamb and wool, are the real culprits behind the
As evidence, the study points to a 141-percent increase in wages, 23
percent decrease in lamb prices, and 82 percent decrease in wool
prices during the period in which sheep numbers were reduced by 85
percent. This is an industry whose profitability has been squeezed
from both sides, said WCS research scientist Kim Berger, the lead
author of the study.
If predation losses are responsible for the decline in the U.S.
sheep industry and federal predator control has been effective at
reducing these losses, then we’d expect to see a strong, positive
relationship between efforts to control predators and trends in sheep
numbers and that is just not the case, said Berger.
Berger notes that while predation is not the industry’s primary
threat, it is one of the few factors over which ranchers feel they
have some degree of control, and this can lead to intense pressure on
wildlife managers to reduce predator numbers. In 1998 alone, federal
agents killed more than 268,000 large carnivores, according to WCS.
Although coyotes account for 75-to-95 percent of carnivores killed
annually, mountain lions, bobcats, wolves, black bears and grizzly
bears are also removed. The perception of carnivores as widespread
livestock killers represents a major challenge to their conservation
Berger suggests that federal funding for predator control in the
sheep industry should be re-evaluated given the program’s failure to
prevent the industry’s decline. That the decline of the sheep
industry is closely associated with unfavorable market conditions
rather than predation losses raises serious doubts about the value of
continued efforts to control carnivores, Berger said.