Proceedings of the Vertebrate Pest Conference

Development of techniques to apply ground squirrel bait by aerial application has been under way during the past three years, with 150,000 acres of rangeland treated in San Luis Obispo County, CA, during 1966. The types of suitable aircraft and application equipment are discussed, as are application techniques. Using crimped oat groats treated with sodium fluoroacetate (Compound 1080) at concentrations of 0.056 - 0.113%, efficacy has been good to excellent (90% or greater). Advantages of aerial application and the use of sodium fluoroacetate are discussed.

The history and development of rodent control systems in northern California, particularly in regard to ground squirrels (Spermophilus spp.) and meadow mice (Microtus californicus) are discussed, with the work of “pest abatement districts” described. A bounty system intended to control ground squirrels and pocket gophers had been enacted in 1870, it but was soon abandoned as too expensive and ineffective by most counties. In 1874, new legislation resulted in certain counties establishing Squirrel Inspection Districts while requiring landowners to control ground squirrels, but this system was neither widely adopted nor effective. Finally, in 1917 a state Rodent Control division was established that resulted in effective action, and improved methods and techniques have continued to be developed. In the late 1950s, studies of Microtus in the Tulelake Basin resulted in a better understanding of the dynamics of meadow mouse damage and population cycles, resulting in improved control strategies. County-led efforts and their effectiveness are described. Current techniques have advantages of being increasingly species specific with reduced hazards to nontarget species, particularly raptorial birds.

To fulfill the primary objective of the Vector-Borne Disease Section of the National Communicable Disease Center (CDC) − to reduce the incidence of vector-borne diseases − a series of courses on vertebrates and arthropods and their role as reservoirs, vectors, and disease-causing agents is presented. Literature is prepared and a museum is maintained. One of these courses, Epizootic Ecology, illustrates some of the aspects dealt with in these courses. Definitions and concepts are presented followed by a brief review of principles of epidemiology and ecology. Specific examples constitute the bulk of the course. One of these, tularemia, is especially useful for the purposes of this course in that it occurs in many nidal centers throughout the world, each nidus having different hosts, vectors, and cycles in nature, which affect man differently. The course concludes with a classroom discussion dealing with ecologically oriented control measures.

Since the report on our understanding of plague in California as reported in 1964, the largest outbreak in the state since the early 1940s occurred, which largely proved the assumptions stated in the earlier report. An infected chipmunk was found on the north shore of Lake Tahoe (Nevada) in August 1965; a human plague case occurred at Viola, southeastern Shasta County in September 1965, that was linked to an epizootic in California grounds squirrels nearby; and in 1966 plague was confirmed in three woodrats in the Tulare County foothills, where California ground squirrels were found also be involved at several locations. By late spring, plague was detected in chipmunks and golden-mantled ground squirrels in Shasta and Mono Counties. The role of various species serving as reservoirs and casualties of plague infection is discussed in detail, along with a description of investigations and actions taken by county and state public health personnel. The role of wood rats, the occurrence of epizootic migrations, and the effectiveness of control measures are discussed.

This history of rabies in California wildlife is reviewed, noting that in the state there have been cases of rabies occurring in canids (coyotes, foxes), bobcats, skunks, and bats, in particular. The current problem of sylvatic rabies in the state, which materialized by the mid-1950s, is emphasized. Long-term cycles of rabies in wildlife are poorly understood. Data regarding animals diagnosed with rabies in California by specie and by county are reported for the period 1952 through 1966. While it is noted that the state’s requirements have successfully controlled and prevented rabies in dogs, California lacks a program of organized rabies control in wildlife. It is suggested that the Division of Wildlife Services within the Bureau of Sport Fisheries &Wildlife - USDI, if provided state funding to conduct sylvatic rabies surveillance and control, would greatly assist in managing this growing concern.

The responsibilities for good practice in pest control is share among the general public, government agencies, and industry. The responsibilities appropriate to each of these groups is discussed in some detail, particularly in regard to the growing pest control industry in the U.S., and in particular, those within the industry who control wildlife damage. Among topics discussed are sanitation and other non-chemical means of pest management and control, guides to the safe use of pesticides, and the labeling of service containers (e.g., bait stations).

Chemical repellents for both mammal and bird damage management are reviewed, with emphasis on recent research progress at the Denver Wildlife Research Center. Improvements in the process of chemical screening are described. Of more than 8,500 chemical compounds tested at both the Denver and Patuxent Research Center, no suitable repellents for use in product packaging has been found. Studies on repellents to reduce animal damage to wire and cable, especially to buried cable by pocket gophers, are under way. While little progress has been made on identifying compounds that are successful area repellents against mammals, contact repellents to protect plants in both agriculture and forestry applications have shown some success against rabbits and deer. Some success in repelling birds from seed and sprouting seed has been achieved in field tests. Recent literature citations are given.

The mission of the Branch of Animal Control, Division of Wildlife Services, Bureau of Sport Fisheries & Wildlife, U.S. Department of the Interior, is discussed. While there is an ever-increasing need to protect agricultural products both at home and abroad, as well as to protect human health and safety, there is also a real concern to reduce impacts of animal control on the environment and on nontarget wildlife, in particular. We need techniques and materials that are more selective, and control needs to be based on demonstrated need. Compound 1339 is in the last stages of registration and promises appreciable relief from starling problems, particularly in feedlot situations. Compound 714, “Gophacide,” has been registered and will serve as a replacement for Compound 1080 in the control of certain burrowing rodents, as it substantially reduced secondary hazards. Compound 1080 remains the most effective and selective tool for controlling coyotes., with significant advantages over strychnine or trapping. Aerial hunting is now used more than ever and is a selective method. The agency’s new responsibilities in the areas of pesticide surveillance and in wildlife enhancement are discussed.

The history of introduction of Rattus species onto Pacific islands and their management are discussed. The Polynesian rat was transported among inhabited islands by Micronesians and Polynesians in their outrigger canoes. The larger roof rat was less widely distributed prior to World War II, and where resources are limited, locally it may push the Polynesian rat to extinction. The Norway rat does poorly in most tropical areas and is restricted to warehouse, dock, or residential areas. At Eniwetok Atoll in the Marshall Islands, Polynesian rats were probably the only rodents present until after WW II, when roof rats were brough in along with supplies and equipment for the atomic testing program in the late 1940s or early 50s. It is speculated that Polynesian rats were exterminated by the atomic blast that denuded the island, while roof rats likely survived within protected cable tunnels or under concrete structures.

Blackbirds in Ohio and other areas of the Midwest have diets of which 90% is composed of soft seeds, primarily the milk and dough stages of corn, during the late summer and early fall. Presently, economic loss of $15 million bird depredation to crops is estimated for Ohio, while other states report similar losses. Increasing losses, primarily to redwing blackbirds, were noted by farmers following World War II. Formal studies of this growing problem were initiated in 1957, with work focusing on poisoning blackbirds, testing scaring devices, trials of bird-resistant crop varieties, and studies of the basic biology of blackbirds. Studies on bird movement and nesting revealed that the largest number of locally raised redwings were produced in alfalfa fields: 5 times as many nests per acre than in cattail marshes. Roost surveys indicated an explosion in the redwing population. Among corn farmers in norther Ohio, organizations emerged to press for increased research and assistance to combat the growing losses. As a result, better loss assessment estimates were achieved, educational efforts were increased, and federal assistance is now more readily available.

This paper provides a detailed analysis of bird damage assessments to detect crop loss in corn. Measurement criteria, methods of loss calculation, and rate of sampling are discussed. In planning a strategy to measure crop loss, one needs to take into account distribution of damage as well as variation in measurement.

Field trials involving two chemical bird frightening agents are described. DRC-736-treated cracked corn was tested in feedlots in Colorado to reduce damage by redwinged blackbirds, and it was considered to be very effective. Sharp reductions in bird numbers occurred immediately after each baiting, and populations at feedlots remained very low for several weeks after treatment. 4-aminopyridine (DRC-1327) was evaluated in reducing blackbird damage to ripening corn using two different methods, either spraying ears or using broadcast baits, and in both trials was successful. Only a few frightened birds were needed in a field to frighten away others in the flock.

An understanding of bird behavior is needed in order to approach solving bird damage problems. Behavior of blackbirds (including starlings, grackles, and cowbirds) is discussed in detail in relationship to roosting, movement, food habits, and the seasonal changes involved in these behaviors. Responses to frightening stimuli, particularly biosonics such as alarm calls, are discussed.

A field trial is described in which sudan black, a known embryocide, was inserted into fish used as bait for herring gulls on Muskeget Island, Massachusetts, in order to reduce reproductive success. Two baiting strategies were compared: remote (at major garbage dumps on Cape Cod), and proximate (over the eastern half of the island). Both treatments showed effectiveness in reducing reproductive success. The economics of conducting such a treatment to sterilize virtually the entire herring gull population in New England are discussed.

The growing problem of wildlife damage in urban and suburban areas is discussed. Some tools and techniques useful in more rural areas are not appropriate for use in urban settings, because of potential nontarget hazards, potential complaints about noise, or other reasons. Control methods recommended in suburbia are often less effective, more time consuming, and more costly the methods used in rural or agricultural areas. Solutions to urban and suburban problems with rabbits and jackrabbits, pocket gophers, moles, ground squirrels, tree squirrels, skunks, opossums, raccoons, and bird are discussed.

Sources of supply for materials and tools used in wildlife damage control are provided in an exhaustive list of manufacturers and retailers, including bird control devices, live traps, mole traps, rodent traps, snares, and leghold traps. Rodenticides, burrow fumigants, and animal repellents are listed by manufacturer/supplier.

Research into problems of bird hazards and aircraft is said to have begun following a 1960 crash of a turboprop aircraft in Boston, killing 62 people. The problem of bird-aircraft strike is discussed, and data on bird strikes are presented for the U.S. for the years 1962-1963 according to aircraft type, altitude, species of birds involved, and costs of damage. Bird control methods in use at airports, as reported in a 1966 survey, are compiled and discussed.

The role of the farm advisor (county agent) in vertebrate pest control is discussed, with personal examples from San Mateo County, CA. Agents of the Agricultural Extension Service (Cooperative Extension) affiliated with the state’s Land Grant University serve in the capacity of assisting and facilitating research, conducting and facilitating education and training, and serving as a liaison for clientele as well as for those involved in wildlife damage management.

Research efforts to combat the problem of European starling damage in livestock feeding areas (feedlots) by developing appropriate toxicants and stupefacients are described. Of about 500 chemicals screened for possible utility, 4 compounds showed promise at potential toxicants for further development and testing: TEPP (tetraethyl pyrophosphate), DRC-632 (0-[4-(methylthio-m-tolyl] phosphorothioate)), DRC-1327 (4-aminopyridine), and DRC-1339 (3-chloro-p-toluidine hydrochloride). TEPP was found to be too toxic to mammals to further develop its potential use against starlings. However, because it causes rapid death, it was useful in subsequent tests of bait acceptance by various avian species. DRC-632 was the first material noted to be far more toxic to birds than to mammals. Dermal toxicity proved more important than oral toxicity, but its extreme secondary hazard, especially to avian predators and scavengers, made it generally unsuitable for use. DRC-1327 was found to cause birds to emit distress cries and violent reactions in birds ingesting the materials, which often died, but also causing flocks to abandon the treated area. Field trials showed promise, and when bait acceptance by starlings is poor or fair, it is more effective than other known toxicants in reducing damage. DRCC-1339 (Starlicide) is the most selective bird toxicant presently known, providing starling control that is virtually nonhazardous to other animals. Discussions of bait materials and formulation, active ingredient dilutions, and baiting methods are provided.

Growing populations of starlings have been causing increasing summer damage to grapes and figs in Tulare County, CA, since 1960. Losses in specific grape plantings range from “slight” to nearing 80% loss. Trials of various control methods have shown mixed results. Of the most successful are trapping, or trapping combined with toxic bait. Where statis populations occur, or where starlings stage or gather before going to roost, the modified Australian crow trap has shown success. Exposing bait (fresh grapes, or raisins dipped in a toxic solution of DRC-1339) in conjunction with the use of a trap as a decoy cage has proved promising. Where trapping or baiting are not feasible, some sites have been adequately protected using carbide or acetylene exploders or even shell crackers.

Live traps have been used successfully to trap European starlings causing damage to cherry orchards in Washington State since 1960. The most suitable trap is a modified Australian crow trap, and we have acquired such a trap mounted on a trailer, capable of being handled by one man. On several occasions, this trap has rapidly reduced local flock buildup and contributed greatly to crop protection.

A cooperative program to control European starling damage in feedlots in California has been developed among the CA Department of Agriculture, the county agricultural commissioners, the U.S. Bureau of Sport Fisheries and Wildlife, and the University of California. Pilot starling control programs using avicides began in winter 1963-64. A description of a developing bait program is given, using DRC-1339-treated grain or raisin baits, exposed in V-troughs mounted on cages containing live starling decoys or on the ground adjacent to a pond. When cold nights limited decoy survival, baits were exposed near mangers, positioned so that starlings were exposed to baits as they first entered the feed bunkers. Baiting strategies and starling behavior in relation to baits are described and discussed. At one feed lot, calculations estimated that well over 5 million starlings were killed by baiting operations.

Progress on winter starling control projects conducted by the Division of Wildlife Services (U.S. Bureau of Sport Fisheries and Wildlife) during the early to mid-1960s is reported. Trials used the toxicant DRC-1339, which is described in terms of toxicity, selectivity, and experimental use. During winter 1964-65, some very spectacular results were obtained from large-scale field tests of feedlot baiting in the western U.S. Details of successful field trials conducted in Idaho, Nevada, and Oregon in the mid-1960s are described. In some instances, dogs and hawks fed on carcasses of poisoned starlings, at times in considerable quantities, with no ill effects. DRC-1339 -treated bait diluted with untreated bait has been widely and successfully used; undiluted bait generally gave poor to fair results. Emphasis cannot be stressed too strongly on the importance of knowing bird behavior and habits within the feedlot to be baited. Also, with an increase in severity of winter weather comes a directly related increase in bait success.

A program to control black-tailed jackrabbits, which caused considerable damage to a vegetative conversion project that transformed sagebrush rangeland to drought-resistant grasses, is described. On this 6,000-acre site in Modoc County, CA, jackrabbits were controlled by use of portable baiting stations containing either oat, barley, or sliced apple formulations of a strychnine bait, preceded by prebaiting. About 90% of the kill occurred, following prebaiting, on the first night of toxic bait exposure. Bait stations were enclosed within portable deer and cattle-proof baiting pens. This method of bait application was considered to be about as effective as the trail baiting method, but with less hazards to nontarget wildlife. Despite control success, adequate jackrabbit reduction was overshadowed somewhat by reinvasion from adjacent sagebrush areas. Specifications for portable baiting pens, bait stations, and bait formulation recipes are provided.

The organophosphate compound recently registered for pocket gopher control under the trade name Gophacide (DRC-714) is described and characterized according to mode of action, toxicity, and efficacy. Formulations on grain at 0.1% and 0.2% give good bait acceptance and achieve high mortality in field tests on all gopher species except the Mexican pocket gopher. It is superior to common rodenticides for gopher control, with less hazard to nontarget animals than some other rodenticides, and it has slower action and available antidotes. It shows promise for controlling meadow mice, house mice, kangaroo rats, and pine voles. While black-tailed jackrabbits are highly susceptible to the compound, it presents a secondary hazard to eagles and large hawks.

Biotelemetry is a new tool that has become available to wildlife biologists within the past decade, thanks to recent advances in miniaturization of components such as transistors, mercury cell batteries, and printed circuits, allowing animals to be fitted with radio-collar transmitters. Current studies of toxic baiting for control of mountain beavers, jackrabbits, and nutria are employing this technology. The new technology expedites control evaluations and is far less costly than previous methods in obtaining needed data.

The principal forest rodent control efforts, which attempt to reduce or prevent rodent damage to reforestation efforts, are described in terms of historical development and current practice. Following logging, the open canopy phase of forest rotation often creates environmental conditions that lead to dramatic increases in rodent damage. Investigations have helped develop information concern tree seed losses to rodents. Through field trials, a better understanding of the use of endrin as a seed repellent was obtained, including observations that mice “learned” to avoid endrin-treated seeds. Studies have also revealed more details about population levels and encroachment by seed-eating rodents such as Peromyscus maniculatus, Clethrionomys californicus, and Reithrodontomys. Future research needs regarding rodent control in forest habitats are discussed. Literature citations are provided.

This paper provides an in-depth understanding of the concept of biological control (biocontrol). In doing so, it interprets important biological principles of control methodology, and it intercalates these discussions with analysis of the biological backlashes and other ecological interactions that may be created whenever vertebrate “pests” are control by biological means. The concept “balance of nature” is explained, noting that only in the most remote area is human impact on the environment not present. The term “biological control” is defined as an attempt to reduce the population density of a pest species (e.g., increase mortality, reduce natality, or cause significant emigration) either by increasing predation, changing habitat conditions, introducing or stimulating epizootics, or by use of antifertility agents. The dynamics of vertebrate population are examined in detail. Detail discussion in provided on predators (both native and introduced), habitat modification, diseases, and chemosterilants, in regard to both mammals and birds. The greatest likelihood for effective application of biological control of existing pestiferous vertebrate populations is by means of integrated control (i.e., where biological control is done concomitantly with an initial population reduction by some conventional control method). An extensive literature review is provided.

This paper updates a 1964 review of vertebrate pest problems and control techniques used in the Republic of South Africa. Appreciable progress has occurred within the past few years, with assistance provided by the U.S. Fish and Wildlife Service. Methods for controlling damage caused by the major predators, the black-backed jackal and the Cape baboon, are described. For jackals, useful techniques include hunting with packs of hounds, use of traps, and use of toxicants, including the coyote getter. Successful lures to attract jackals to coyote getters are described. Baboons, which are gregarious and form troops numbering from a dozen to over 100 individuals, cause extensive damage to vineyards, orchards, and vegetable crops, and at times kill lambs and young goats. Destruction of the baboon’s major predator, the leopard, is blamed for recent rapid increases in baboon populations. Successful use of the toxicants thallium sulphate, Compound 1080, and Telodrin against baboons are described. Damage and control practices associated with the dassie (hyrax) and dune mole are discussed. Introduced American gray squirrels, while limited in distribution, are known to have become firmly established and are a major predator of the nests of songbirds, as well as damaging pine plantations and orchards. Feeding habits of the cape vulture, which normally eats carrion, have changed and these birds are now periodically killing lamb and ewes, especially those in poor condition, perhaps due to food scarcity.

Motivations and human behaviors that have resulted in importation of nonnative wildlife to North America, as well as other locations, are discussed. Historical attitudes, including immigrants’ desires to see birds and other wildlife from their homeland, led to societies whose goal and purpose was to introduce songbirds and other species. Biologists, including C. Hart Merriam, opposed these introductions, as noted in his writings as early as 1886. Certain British colonies began to take note of the negative impacts of introduced species in the late 19th Century; for example, Western Australia passed the “Destructive Birds and Animals Act” in 1890. Despite the efforts of many, no significant federal legislation was in place in the U.S. until the Lacey Act passed in 1900, which was expanded by subsequent amendments in 1935 and 1960. In recent times, the advent of increased global trade and commerce, as well as air travel, brings new challenges in preventing accidental or intentional important of species that may be very destructive when placed in new environments.