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Open Access Publications from the University of California


The concept of the Vertebrate Pest Conference originated in early 1960 from discussions among representatives of the University of California; the California Dept. of Fish & Game; the California Dept. of Agriculture; the California Dept. of Public Health; and the Branch of Predator and Rodent Control, Bureau of Sport Fisheries and Wildlife, U.S. Fish & Wildlife Service. The original participants recognized that few published documents on vertebrate pest control were available, as such information was typically contained within in-house reports of the various agencies that were largely unavailable and unable to be cited. Dr. Walter E. "Howdy" Howard of UC realized that having a conference would permit a Proceedings to be published, in which this information could be made widely available.

To plan such a conference, the organizing group, chaired by Dr. Howard, became the Vertebrate Pest Control Technical Committee, which arranged and hosted the first "Vertebrate Pest Control Conference" held in Sacramento on February 6 & 7, 1962. The planning committee formally became an incorporated non-profit entity in 1975, and the Vertebrate Pest Conference is now held in late winter or early spring every two years. It is the most widely-recognized conference of its kind worldwide.

Detailed histories of the development of this Conference are found in these publications:

Salmon, Terrell P. 2012. VPC: Fifty Years of Progress? Proc. Vertebr. Pest Conf. 25:3-6.

Marsh, Rex E. 2008. A History of the Vertebrate Pest Conference. Proc. Vertebr. Pest Conf. 23:310-326.

Gorenzel, W. Paul. 2004. Opening Remarks - A Retrospective Look at the Vertebrate Pest Conference. Proc. Vertebr. Pest Conf. 21:1-2.

Howard, Walter E. 1982. Twentieth Anniversary of Vertebrate Pest Conferences in California. Proc. Vertebr. Pest Conf. 10:235-236.

Howard, Walter E. 1962. Opening Remarks – Vertebrate Pest Control. Proc. Vertebr. Pest Conf. 1:1-7.


Vertebrates: A resource needing management

In this keynote address, a case is made for continued effort at finding new and improved ways to manage vertebrate pest problems in increasingly man-modified environments. However, this is met with objections by those promote a hands-off philosophy: “Leave Nature to her own devices.” The author lists four basic needs for managing vertebrate populations: 1) Certain vertebrate post imminent hazards, because of their lethal defense mechanisms or their role as disease vectors; 2) Wildlife competes with man for food, in terms of growing crops or stored foods; 3) Vertebrates frequently require management of their populations for their own benefit; and 4) Vertebrate populations require control when they get out-of-balance and exert adverse effects on associated species that man is endeavoring to perpetuate. The author discusses examples and case histories from throughout North America, noting that societal attitudes toward animal control and pesticides are changing, and the credibility of professionals in wildlife management is sometimes challenged or lost to environmental emotions.

The extending of cotton rat range in California - their life history and control

Cotton Rats (Sigmodon hispidus eremicus Hearns) are known to have reached the Imperial Valley in 1921 from the Colorado River along canal banks. Recently (1967-69) cotton rats were found distributed throughout the irrigated portion of the Imperial Valley, Imperial County, California. Limited crop damage has occurred and is described. Life history information is included. Control measures are listed.

Status and control of nutria in California

Although feral nutria (Myocastor coypus) have been present in California since the mid-1940's, they are quite scarce and at present are causing little or no agricultural damage. Present state regulations and pest detection activities will probably prevent them from becoming a serious economic pest. Should control ever become necessary, studies in other areas indicate that shooting, trapping, and baiting with zinc phosphide should be effective.

Muskrats in central Europe and their control

An account of the introduction of muskrats into Europe and their spread over the countries of Europe is presented. The reasons why the animal should be controlled are discussed. Legal regulations often do not keep up with the requirements and economic and political circumstances and frequently have encouraged the spread of muskrats. The use of traps alone does not solve the problem of their control. Therefore, research is looking for suitable poisons and a good practice to apply them. At present this question cannot be answered satisfactorily.

The need of surface sprays for the control of microtine rodents

Four Microtine species, the field vole (Microtus agrestis), the continental vole (Microtus arvalis), the water vole (Arvicola terrestris) and the bank vole (Clethrionomys glareolus) are the most harmful rodents in forests, fields, orchards and gardens in Northern and Central Europe. Except for the latter they are all herbivorous, their food consisting to a very low degree of seeds and grain. As a consequence, dry poison baits are not well accepted most of the year. The only economic and effective control method until now has been surface spraying with the chlorinated hydrocarbons endrin and toxaphene. As these chemicals are now black-listed in many European countries, and their use severely restricted in other countries, no effective means for controlling these rodents exist for the time being. New surface sprays without the persistence of endrin, but with a more long-lasting effect than parathion, are severely needed if the extensive damage to trees and crops shall be reduced.

Protecting coniferous seeds from rodents

For almost a half century now, repeated failures in direct seeding operations on cutover forest lands in North America had been largely blamed on the unproven destruction of the seed supply by small mammals. In 1960, the Canadian Wildlife Service undertook a research project to ascertain the possible fate of white spruce seeds placed into the natural environment and the influence which small mammal populations may have upon such a seed supply. By equipping each seed with a microscopic radio-transmitter (radio isotopes), the seeds could be left in the field for up to one year and then recovered intact or as seed coat fragments to provide data on seed fate. Recovery success on 21,800 white spruce seeds in ten years of study has been 90%. Recoveries indicate near 50% of spring sown seeds could be destroyed by small mammals within 17 weeks in some years despite the fact that these seeds had been previously treated with the widely accepted protective coating of aluminum powder-endrin-arasan-latex. Late winter seeding reduced losses to small mammals by 2/3. No direct relationship between numbers of small mammals present and the number of seeds destroyed could be demonstrated. A critical examination of seed treatment procedures widely used has led to the development of a new seed coating formulation employing a potent rodent repellent, R-55. Under laboratory conditions, the new coating yielded improved germination and a high degree of protection against small mammals. The new coating treatment received limited field testing during 1969 and is currently undergoing refinement and more extensive laboratory and field testing in Alberta.

Methodology for measuring taste and odor preference of rodents

Taste enhancers and olfactory attractants are needed to improve bait acceptance for rodent control, but most methods for evaluating preference for taste and odor stimuli are not suitable for screening large numbers of such compounds. This paper describes two automated preference testers designed for this purpose. The taste preference apparatus is based on the principle of the brief-exposure, foods-together technique, whereby the animal briefly samples each food alone, in alternate sequence, before the two foods are presented together, in alternate positions. The odor preference tester is based on an open-field maze, whereby the test animal samples each of four odor sources before preference behavior is recorded. Both devices are fully automated (in both operation and data recording), are free of position bias, and produce preference determinations in relatively little time; neither requires special training of test animals. The design, operation, and application of each apparatus in rodent control is discussed and illustrated.

The strategy for controlling rodent damage to pines in the Canadian Mid-west

The transitional zone between prairie and boreal forest in Manitoba and Saskatchewan is more suited to the needs of forestry than to agriculture. Tree production is difficult in this zone for a number of reasons, one of which is the depredations of small mammals, especially the meadow vole, Microtus pennsylvanicus (Ord). Vole populations peak every 3 to 5 years and on the average irruptions of serious importance occur about every 10 years. Populations in the transitional zone are generally higher than those in the treed areas of adjacent zones: areas of extreme populations coincide with areas of greatest forestry concern. Key factor analysis indicates that a high degree of damage predictability may be achieved by measuring juvenile vole survival. Spruce, jack pine, white pine, red pine and Scotch pine are increasingly vulnerable to rodent damage. Seed and stand density also influence degree of impact. Strategy of vole damage control must involve prediction surveys coupled with cultural, operational, and baiting tactics.

Barrier fencing in wildlife management

Barrier fences have been used to control animal and human depredations since ancient times. They have exerted considerable influence upon the culture of the "protected" areas even though protection was rarely complete. The following materials have been used in construction of fences: earth, vegetative materials, wire, electric shock, and synthetic materials. Fence designs must consider the size, strength, intelligence and/or instinct, and physical agility of the species to be repelled as well as the attraction of the crop or area for potential depredators. Against deer, the 8-foot upright, vertical overhanging, outrigger and sloping fences are more successful than electric fences. The larger predators are difficult to control with fencing. Net wire fencing of ½-inch mesh is needed to keep all small predators out of the poultry yard. An L-shaped poultry netting fence topped with a hot wire has been found generally successful in protecting field crops against both carnivores and rodents. Lagomorphs can be contained with fences 30 to 36 inches high, but they must be buried at least 6 inches underground to prevent digging under.

A preference-testing system for evaluating repellents for black-tailed deer

In a program to evaluate repellents for protecting Douglas-fir (Pseudotsuga menziesii) seedlings from browsing by black-tailed deer (Odocoileus hemionus columbianus), a preference-testing system was developed to supplement preliminary pen tests. The system uses an apparatus that presents individual test deer with a choice between two foods (usually feed pellets treated with a candidate repellent or a marginally palatable standard). The two foods are presented, in alternating positions, only long enough for the deer to make a choice; results are recorded in terms of percent choices made for the candidate repellent, or percent consumption. Tests thus far with a number of candidate repellents, including several chemical fractions derived from putrefied fish, have generally given clear-cut results, and the system appears very promising for this kind of evaluation. Although semi-tame deer and an experienced operator are required, the system uses very small amounts of candidate repellents, produces evaluations on a material in 1 to 2 days, can be used year-round, and permits observations of deer behavior during the choice process.

Good practice statements -- developing guidelines for the safe and efficient use of pesticides

Because pest control, vertebrate and invertebrate, is an applied science, a disciplined technology is mandatory. The National Pest Control Association, through its technical committees, is developing guidelines for the safe and efficient use of pesticides and for the execution of specific forms of pest control. These guidelines known as "Good Practice Statements" not only reveal a methodology utilizing the cooperative efforts and experiences of commercial pest control operators, representatives of the scientific community, and specialists from pertinent governmental regulatory agencies, but in themselves as physical documents add to the total expertise of everyone connected with the problems and responsibilities of conservation and control of the environment.

Related laws on exotic and native wild animals

This paper is submitted in an effort to acquaint the personnel of allied State agencies with related laws which control the public and private possession of live exotic and native wild animals. The need for this common knowledge of related laws by agencies with law enforcement responsibility is readily apparent when the annual number and related problems from imported or resident wild animals in California are examined. In addition to resident wild animal populations, millions of fish and thousands of mammals, birds, and reptiles enter California each year through the utilization of most methods of transportation. Most of these imported animals are exotic species from foreign lands which cannot be readily identified and pose various degrees of potential and actual threat to native wildlife, agriculture, and public health if they are introduced into the wilds of this State. For the purpose of this report, a general picture of imported exotic animals is presented in an introduction, and specific animals with related laws are treated individually under the headings of current laws and future regulations.

The Oregon ground squirrel in northeastern California: Its adaptation to a changing agricultural environment

As early as 1918, populations of the Oregon ground squirrel (Citellus oregonus Merriam) were reported to be increasing in northeastern California, presumably because of "the extensive clearing of the sagebrush and seeding of these clearings to grain and hay." Populations of this locally important field rodent have continued to increase since that time with the further development of agriculture. Observations of the author during the past quarter of a century indicate that ground squirrels in the most intensively farmed areas are changing their habits, and they may be evolving into an ecotype markedly dissimilar to that which existed in the pristine environment.

Zinc phosphide - a new look at an old rodenticide for field rodents

Of the many toxicants tested to control field rodents, compound 1080 (sodium monofluoroacetate), strychnine alkaloid, and zinc phosphide are the only effective single-dose rodenticides currently available. Considering the federal requirements for use in food and feed crops, zinc phosphide is the toxicant most likely to be registered for field rodent control. It is generally well accepted by rodents, is relatively safe for nontarget species, and does not seriously contaminate the environment. It is already registered, with an established tolerance, for use in one food crop (Hawaiian sugarcane). The Bureau of Sport Fisheries and Wildlife is conducting research, some in cooperation with other agencies, to register zinc phosphide for controlling: prairie dogs (Cynomys ludovicianus) in shortgrass rangeland; jackrabbits (Lepus californicus) along cropland-rangeland borders; cotton rats (Sigmodon hispidus), rice rats (Oryzomys palustris), black rats (Rattus rattus), and Florida water rats (Neofiber alleni) in Florida sugarcane; ground squirrels (Spermophilus spp.) and meadow voles (Microtus spp.) in alfalfa, sugarbeets, artichokes, and rangeland.

Experimental population suppression of Richardson's ground squirrels (Spermophilus richardsonii) in Alberta

Richardson's ground squirrel is one of the most economically harmful rodents in east central Alberta. In an effort to develop an effective, safe, economical and practical method of long-term population control over large areas, experimental field testing was begun in 1970 to evaluate a variety of potential control techniques. Although tests with a machine bait applicator proved unsuccessful due to the unique soil structure, its potential in other areas of the province is discussed. Use of portable baiting stations is limited by the manufacturing and maintenance costs as well as the limited attractability of the stations. Attractability of the stations to ground squirrels was not increased with the use of reflector tops; however, it did have a repellent influence on raptors feeding in the area. Disposable baiting tubes appeared to have greater potential for large acreages and possible aerial application. Initial tests conducted with diethylstilbestrol and mestranol as chemosterilants are outlined. The potential of using techniques to regulate reproductive rate as opposed to increasing mortality rate is discussed. The potential of using amphetamines to reduce body weight and increase winter mortality during hibernation is also discussed.

Vertebrate pests in New Zealand: Research and control

New Zealand, by its isolation, evolved a unique fauna in the absence of humans. With essentially no native mammals, it evolved a diverse fauna of flightless birds, while many of its native flighted birds nested on the ground. The Polynesian immigrants and the Maoris began changes to the environment that led to extinction of some species, but in the early 19th Century, European colonists introduced many mammals that have had appalling negative effects on the New Zealand environment. Damage to flora and the environment by European rabbits, hares, possums, deer, chamois, and tahr is described. Government efforts to control the Australian brush-tailed possum began in the 1940s and are described, with emphasis on the use of sodium fluoroacetate (1080).

The extension trapper system in Kansas

The Extension Trapper System instituted in Kansas is described. Developed within the Extension Division, the off-campus arm of Kansas State University, it involves an education effort to teach landowners and land managers how to manage wildlife damage, focusing on livestock predators. Improved livestock management practices, coupled with selective removal of problem coyotes by landowners who have been taught to utilize traps and other tools, has successfully reduced coyote predation on livestock statewide.

Methiocarb, a chemical bird repellent: a review of its effectiveness on crops

Since 1964, when the effectiveness of methiocarb for preventing pheasants (Phasianus colchicus) from damaging sprouting corn was proven in South Dakota, an aggressive program has been carried out by personnel of the Denver Wildlife Research Center and many cooperators to develop methiocarb as a broad-spectrum avian repellent. The successful use of methiocarb for preventing damage caused by several species of birds to sprouting corn in several states and to sprouting soybeans in South America is reviewed. Recent results obtained from spraying methiocarb on ripening rice in California, ripening sorghum in Colorado and Oklahoma, cherries in Michigan, and grapes in New Hampshire are summarized.

Some approaches to controlling depredations by crows and jays in Tulare County

The biology and behavior of the common crow and the scrub jay in Tulare County, California, are described in relation to damage occurring in orchards. Crow damage to almonds and walnuts is noted, as is scrub jay damage to pistachios. Methods of bird control that have been attempted, including frightening devices and use of Starlicide®, are discussed

Bird damage to peanuts and methods for alleviating the problem

Investigations from 1969 through 1971 of bird damage to peanuts in south-central Oklahoma have shown that losses are caused mainly by common grackles (Quiscalus quiscula). These losses, as high as $36 per acre, have been reduced primarily through the use of exploders and early harvesting of the crop. A fright-producing chemical, 4-aminopyridine, was also effective in scaring grackles from windrowed peanut fields. Banding has shown that many of these grackles breed in western Nebraska and Kansas and winter in northeastern Texas.

Factors relating to alarm stimuli in bird control

The use of alarm stimuli as a means of bird damage control is discussed. Effectiveness is dependent upon a number of factors, including environment, bird vulnerability to attack, time-of-day, physiological requirements, and the bird species’ social structure. Some species of birds respond well to alarm sounds, while others do not. Further experiments on the utility of alarm stimuli as a damage management tool must be conducted at various times and under diverse conditions to arrive at definite conclusions.

Starling control in Sonoma County

The introduced European starling began its range expansion into California as early as the late 1930s, and by 1954 it was reported that about 20,000 starlings were spending the winter in or near the Sonoma-Mendocino coast. By 1961, starlings were known to occur in nearly every section of California. Their history in Sonoma County is discussed, including initiation in 1964 of control measures by the County Agricultural Commissioner, at the request of the Farm Bureau. Shooting and trapping efforts are described, as well as evaluations that indicated such control activities were effective in reducing the number of resident starlings in areas of the county. Success in preventing crop damage by use of the Av-alarm device was also noted.

Avian thermoregulation and its significance in starling control

The ability of birds to thermoregulate under a variety of environmental conditions is necessary for their survival. The ability of European starlings to thermoregulate was investigated, finding that this species has a pronounced regular daily cycle of deep body temperature with a range of about 4.5°C. This cycle is likely the result of reduced metabolism and muscular activity during nighttime. A number of experiments of thermoregulation were conducted to better understand the possibility of using wetting agents or other techniques to prevent the birds’ feather insulation from protecting their ability to survive cold weather. We became increasingly impressed with the possibilities of using wetting agents as a possible tool to control birds by application to bird roosts, even under relatively mild climatic conditions that prevail in California.

Efficacy testing of vertebrate pest control agents

Justification for efficacy testing is provided under the present FIFRA, and the PR notice 70-15 requirements. In addition, the Pure Food and Drug Laws, the Delaney Amendment, and other laws effect the requirements of registration of all economic poisons. Basic preliminary registration information such as toxicological data, chemistry data, must be provided on all chemicals proposed as economic poisons. Once the basic chemical and toxicological properties have been determined, the applicant must consider basic efficacy requirements. Efficacy requirements should consider the effects of particle size and shape, taste and odor, impurities, diluents, stickers and solvents, volatility, mode of action, and other factors such as age, sex, species, characteristics and ambient temperatures. Specific studies, however, will vary with the intended use of the product and the target species involved. Field testing is required for all proposed products under actual field situations. These tests logically follow appropriate laboratory tests. The risk-benefit ratio is defined as a ratio of hazards to nontarget organisms as compared to the benefits resulting from the product’s use. At present, this ratio has not been made a part of the registration procedure but has been used in adverse action.

The problem of anticoagulant rodenticide resistance in the United States

While the problem of anticoagulant resistance in commensal rodents has been well-documented from certain areas of northern Europe in recent years, this paper describes its first known occurrence in North America in 1971. Over a rural area of about 5 square miles in Johnson County, North Carolina, it was noted that attempts to control Norway rats using typical warfarin rodenticide bait were increasingly ineffective. Diphacinone was alternated with warfarin with no success. On one farm, 200 lbs of bait had been used in bait boxes in a single month. Laboratory trials on rats captured at this location demonstrated resistance. It was concluded that at this location, intensive use of anticoagulants (mostly warfarin) over a decade, in the absence of adequate sanitation and building maintenance, provided the selective agent to develop resistant populations. This likely will be repeated elsewhere in the U.S.

House mouse behavior and its significance to control

To achieve successful control of an infestation of house mice, one must attempt to interpret the behavior of mice and mouse population, which can differ among locations and circumstances. Using wooden pallets and a combination of sacked grains and corncobs, two arenas were constructed into which first-generation laboratory-reared wild house mice were introduced and observed over a period of 6 months. Social behavior, individual behavior, and population characteristics of the mice were described. The arenas were subsequently used to test mouse behavior in regard to live traps, new foods as potential toxic carriers or trap baits, and to test toxic bait. Conclusions about mouse behavior under different lighting conditions, population density, changes in the physical environment, temperature, and changes in food type as related to control efficacy, are provided.

The influence of attractants and repellents on the feeding behaviour of Rattus norvegicus

Poison baits are extensively used for commensal rodent control; considerable folklore exists regarding the use of additives to induce rodents to come to and eat poison baits. This paper describes a rational evaluation of attractants and the influence of different odours in inducing Rattus norvegicus to feed at given locations. The influence of certain repellents was also examined. Tests consisted of attempts to induce rats to feed at non-preferred sites or to repel them from preferred sites. Place preference was the dominant factor in feeding by rats, and odours failed to Influence feeding activity significantly.

An innovation in roof rat control

Within the past ten years, the roof rat (Rattus rattus) problem in residential Santa Clara County has developed from an insignificant nuisance to one of major concern. When a considerable number of complaints to the Santa Clara County Health Department reported roof rats on telephone cables, a study was made of 29 city blocks to determine the feasibility of utility pole baiting as a means of roof rat control. In the baiting process, rat signs were commonly observed on telephone equipment attached to the utility poles. A correlation was observed between bait consumption and the close proximity of vegetation to the telephone cable clamp. Bait consumption profiles on most blocks demonstrated patterns which resembled activity ranges. During the study approximately 190 two-ounce bait blocks were consumed and many dead roof rats were found by the Health Department and residents living in the baited areas. The procedure appears to be an effective means of population reduction and has the potential of long-range effectiveness.

Rat reduction with indigenous methods

Rat reduction measures were done in 171 villages of Panvel Block in Kolaba District of Maharashtra State, India. It started with rat preventive measures to doors and windows and the spraying of BHC and Malathion around bamboo matting huts. With the onset of rains trapping was done by “Deoras traps” inside houses and poison baiting by zinc phosphide on the outside. Rat burrows were closed by broken glass after the pumping in of BHC 10% dust, or sulphur fumes, or HCN or aluminum phosphide tablets. Lastly as the rains subsided zinc phosphide capsules dipped in melted wax were put on field borders and Malathion 1% sprayed in the field near crops. Total rats reduced were 20,260, of which 17,325 were by trapping and 2,935 by baiting. In the col lection, R. rattus species predominated and female rats were more in numbers than the males in all species of rats reduced. The cost of operations minus the salary and allowances of permanent staff came to Rs. 9,000/-. Public Health and Agriculture aspects were joined together and the rat reduction was done only for four months in the year when the monsoon was on, the paddy fields were full of water, and the rats migrated to residential areas for shelter. Public motivation was done by showing the damage and utilizing the rat skin and meat.

Tolerance shown by Rattus rattus to an anticoagulant rodenticide

Apart from using 0.005% concentration, the recommended field dose of 0.025% of the anticoagulant is used along with an alternate food for individual rats for a varying number of days. Those that had survived were taken as tolerant, provided they showed an mg/kg intake beyond the tolerance limit, survived a six days of feeding, exhibited bait-shyness, and did not exhibit hemorrhage after death. In determining the criteria for tolerance to an anticoagulant by a rat, one should take into account four composite factors. These are, six days of even 0.025% feeding, bait-shyness when alternate food is given, higher mg/kg intake than the tolerance level, and a loss of intensive hemorrhage after death.

Commensal rodent control

Federal Urban Rat Control Program grants were awarded to cities in different areas of the United States. Severe problems of rat infestations have been detected in many of the cities by the Environmental Health Service. Approximately 20% of 3.8 million people in the project areas were occupying homes infested with rats. Control operations are now in effect in all cities, and the living conditions of the people have been substantially improved. An increase in interest in rodent control also is evident in countries outside of the United States. The Technical Development Laboratories of the National Communicable Disease Center are participating in the World Health Organization program of research on new rodenticides. The evaluation program involves five steps which carry a candidate toxicant from laboratory phase through field testing. Acceptability and suitable concentrations of both acute and accumulative rodenticides are determined. Observations are made on the hazard of the compound to pets and to other nontarget vertebrates. Laboratory and field studies have been completed on a new, promising stabilized scilliroside glycoside which has given excellent control of the Norway rat in 16 out of 19 premises. Another new coded compound has shown a unique specificity for roof rats as compared to Norway rats. Although anticoagulant resistant rat populations have occurred in several countries in Europe, as yet no evidence has been noted of such resistance in rats in the United States. (Note: This paper was originally presented at the 4th Vertebrate Pest Conference in 1970.)

What's ahead in predator management

Major changes are about to be made in predator management in the U.S., as a result of the President’s Executive Order No. 11643 of Feb. 8, 1972, and the Report to the Council on Environmental Quality (the so-called “Cain Report”) of the same date. The author discusses these expected changes in light of previous resolutions and policies published by the National Wool Growers Association, the Secretary of the Interior’s Advisory Board on Wildlife and Game Management of 1963-64 (the “Leopold Report”), and statements made by Dr. Stanley Cain before a 1966 congressional hearing on predatory mammal control practices. The author further discusses a recent recommendation that predator control be conducted only by government agency professionals within a U.S. Fish & Wildlife-state government cooperative program, not by private individuals including those who have suffered damage. The author recommends that the Department of Agriculture within California and other western states is the most appropriate agency to conduct predator damage management.