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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 and practice."


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 coyote."


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 to catch.


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 National Park.


"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.

Demographic compensation

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 and breed.

(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.

Alternate prey

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

sheep numbers.


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

industry’s drop-off.


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.