Proceedings of the 3rd Vertebrate Pest Conference (1967)

CONFERENCE PARTICIPANTS

Tue, 20 Dec 2005 07:49:18 PST

The Third Vertebrate Pest Conference was an enormous success with 265 in attendance, of these, 203 were registered participants. The attendance was made up of individuals having varying interests in vertebrate pest problems including foresters, agriculturalists, conservationists, pest control operators, vector control specialists, health officials, wildlife specialists, product distributors and manufacturers, instructors and researchers from twenty three states plus Washington D. C. and South Africa.

CLOSING REMARKS - THIRD VERTEBRATE PEST CONFERENCE

Richard H. Dana — Tue, 20 Dec 2005 07:48:03 PST

The record of this meeting will stand as a tribute to all of those who participated in the Third Vertebrate Pest Conference. It should remind them for years to come of their worthwhile contributions.

FEDERAL WILDLIFE IMPORTATION REGULATIONS: THE WHY AND WHEREFORE

Joseph P. Linduska — Tue, 20 Dec 2005 07:45:47 PST

This is a hasty and in many ways superficial review of the motivations that started us in the business of importing new, strange, beautiful, and hopefully useful wildlife. It is a capsuled account of the high cost of ill-advised introductions and of near misses that were avoided thanks to a few individuals who viewed such transplants with skepticism and even alarm. And I have touched also on the highlights of the legislative base from which we now operate in efforts to safeguard agriculture and other values from ravages of exotic wildlife; wildlife that may succeed too well with us and behave not at all as they do at home. But our best efforts still leave room for caution and concern. With the arrival of the age of jet air travel we have traded one problem for another. In the closing years of the last century our vulnerability centered on a lack of legal authority to control imports. And yet a built-in safeguard may have partly concerned the deliberate travel of ocean liners and the complexities involved in transporting live animals by that means. Today we are less than a day removed from any part of the globe, and the ease and success of moving wildlife by air has greatly increased traffic in many new, unusual and even poorly understood species. The cage bird business has grown explosively. Not the least of our problems now center on inadequate staff to inspect the flood of shipments. And inspections can be involved because working with the bird life of the world (and its fish life, too) can be a job for highly accomplished taxonomists of which there are none too many. Even in the most practiced hands there are problems of identification to flabbergast the experts.

RECENT DEVELOPMENTS IN THE CONTROL OF VERTEBRATE PROBLEM ANIMALS IN THE PROVINCE OF THE CAPE OF GOOD HOPE, REPUBLIC OF SOUTH AFRICA

Douglas Hey — Tue, 20 Dec 2005 07:37:32 PST

In an earlier paper (Hey, 1964 an account was given of the topography and climate of the Cape Province, a description of the vertebrate animals and birds which might be considered to fall in the category of problem animals and the control methods used. The present paper will, therefore, deal with advances in control techniques which have since been made. At this juncture, it would be appropriate to record our sincere appreciation to the Director and Staff of the U.S. Fish and Wildlife Service and particularly to the Senior Officers of the Denver Research Center, District Agents Malcolm Allison and Milton Caroline and the members of their field staff for invaluable advice and assistance in dealing with our problems. Mr. Malcolm Allison spent three months in the Cape Province adapting coyote getter techniques to meet our conditions. At the outset it must be stressed that in contrast to the U.S. Fish and Wildlife Service, our Department does not undertake the direct control of problem animals. The control programme is based on a system of technical and financial aid to existing hunt clubs and local authorities. Any hunting which is done by officers of the Department is merely incidental to the training of hounds or the testing and perfecting of new techniques. The system of technical aid was planned to replace the old bounty system gradually, and this aim has now been realized except in areas where no hunt clubs exist. The Cape Province, covering an area of 277,000 square miles is largely subdivided into farms. State land is chiefly limited to the mountain ranges under the control of the Department of Forestry, and used for afforestation and water conservation purposes. The Province is subdivided into 92 Divisions, each controlled by a Divisional Council which deals with matters such as roads, public health and predator control. The legislation relating to this latter function empowers the Divisional Councils to subdivide their divisions into wards and establish hunt clubs in each. Such hunt clubs are established at the request of the local farmers. The number of clubs in a Division may vary from one to five, depending upon the type of agriculture, the topography and the hunting methods used. The Department of Nature Conservation subsidises the clubs and furnishes technical aid in the form of equipment, trained hounds and undertakes the training of hunters. Periodic inspections of hunt clubs are made to ensure that these are functioning efficiently and to advise hunters on the field application of the latest techniques. While the Department endeavor’s to render all reasonable assistance to clubs, the actual elimination of problem animals is the responsibility of the individual farmers and their hunt clubs. This system is proving increasingly effective and is sound conservation practice, for animals are hunted only when they are a nuisance and not merely for the sake of hunting. The present problems relating to specific animals will now be discussed.

BIOLOGICAL CONTROL OF VERTEBRATE PESTS

Walter E. Howard — Tue, 20 Dec 2005 07:34:15 PST

This paper briefly introduces the subject of vertebrate pest control, integrates and interprets some important ecological principles of control methodology, and intercalates these discussions with analysis of the biological backlashes and other ecological interactions that may be created whenever troublesome species of vertebrates are controlled by biological means. Insight in this area must be deepened if we are to fulfill our primary objective of learning how to manage a healthy environment in perpetuity. One important merit of biocontrol is that most people accept carefully planned ecological dislocations in nature more readily than they do the repugnant and hazardous aspects of eliminating nuisance vertebrates with poisonous materials.

RODENT PROBLEMS ON PRIVATE FOREST LANDS IN NORTHWESTERN CALIFORNIA

Jarrold B. Cone — Tue, 20 Dec 2005 07:32:04 PST

Rodents damage is important to forest management and is adequately described in the literature (Kverno, 1964; Hooven, 1958, 1959; Lawrence, 1958; Isaac, 1943; Kangur, 1954; Tevis, 1956a). It is not the intent of this paper to reiterate the types of damage or the rodents involved; the reader who is interested in this topic is particularly directed to the work of Lawrence, Kverno, and Hartwell (1361). This paper is concerned with the major forest rodent control efforts currently being employed in northwestern California. It will describe the background of literature and investigation from which present practices evolved, the implications that these practices have on forest management, and the indicated future needs for the control of forest rodents.

BIOTELEMETRY — ITS USE IN VERTEBRATE CONTROL STUDIES

Wendell E. Dodge — Tue, 20 Dec 2005 07:29:41 PST

Accurate evaluation of rodent control techniques has always been a laborious undertaking. It generally involves tedious pre- and post-treatment censusing by trapping, marking, track counts, reduction of activity, etc., and results, at best, must necessarily contain a significant amount of speculation by the investigator. The biologist conducting such studies has been constantly harassed by uncontrollable parameters such as trap response, immigration, emigration, predation, disease, and many others. Thus, there has been a pressing need of a more definitive technique for evaluating rodent control trials. During the last decade, a new tool called biotelemetry has become available to the wildlife biologist. This technique has been defined as, "the instrumental technique for gaining and transmitting information from a living organism and its environment to a remote observer" (Slater 1965). As a practical tool, it is still in its infancy. Among its first reported uses in wildlife work were the telemetering of incubating temperatures of penguin eggs by Ecklund and Charltin (1959), a study of salmon movements by Trefethen et al. (1957), and a study of woodchuck movements by LeMunyan et al. (1959). Since these earlier studies, there has been a significant increase in telemetry studies of wildlife. These vary in complexity from simple movement studies to sophisticated telemetry of physiological variables. Many sizes and species of animals have been involved, such as deer mice, large ungulates, marine mammals, thrushes and buzzards. Probably the major obstacle to further advances in wildlife telemetry is the inability of the biologist to meet the cost of development. The cost of telemetric systems can be fantastic and often precludes their use by most investigators. Another earlier limiting factor was the bulk of the necessary electronic equipment to be carried by the instrumented animal. However, recent advances in the development of miniaturized components such as the solid-state transistor, mercury cell battery, and printed circuit, have essentially removed this problem. These, plus the ingenuity of biologically oriented electronics personnel, have made wildlife telemetry possible.

THE STATUS AND USE OF GOPHACIDE

Voit B. Richens — Mon, 19 Dec 2005 15:02:22 PST

Toxicants have been widely used for several decades to reduce numbers of problem animals. The utility of these substances, however, has been limited by hazards to other animals and man, inadequate effectiveness against the target species, and restrictions on use. The ecological complexity of most habitats in which animal control is undertaken requires utilization of new poisons that are less hazardous, more effective, and more specific. Gophacide1, Bayer 38819, 0_, 0-bis(p-chlorophenyl) acetimidoylphosphoramidothioate, is generally favorable in these respects. Tests with Gophacide were initiated at the Denver Wildlife Research Center in late 1961; and more recently, this chemical has also been tested at several field stations under different conditions. The initial and major emphasis has been to determine its usefulness in pocket gopher control. Techniques of use have been described (Ward et al., 1967).

PHYSICAL AND CHEMICAL CHARACTERISTICS: Technical Gophacide is a white crystalline powder which is soluble in chlorinated hydrocarbons, acetone, or warmed corn oil, and melts at 104-106 F. It is an organophosphate, and like related compounds, inhibits the cholinesterase activity of the blood. We don't know yet what the animal metabolites or oxidates of Gophacide are or the activity of such materials. The anticholinesterases, in general, are not accumulated for long periods in fatty tissues, and the hazard to wildlife is considered to be less from chronic than from acute poisoning (Casida, 1964).

A METHOD OF CONTROLLING JACK RABBITS ON A RANGE REHABILITATION PROJECT IN CALIFORNIA

Frank A. Wetherbee — Mon, 19 Dec 2005 15:00:11 PST

In recent years the Bureau of Land Management's range rehabilitation program in the high sagebrush areas of northeastern California has included control of sagebrush preceded by the seeding of drought resistant grasses such as crested wheatgrass. Jack rabbit browsing and uprooting of young seedling plants has in many instances severely retarded the establishment of these grasses. Because of this it has become apparent that rabbit reduction in many of these areas is essential if a grass stand is to become established. A comparison of Figures 6 and 7 illustrates the problems jack rabbits can cause to range rehabilitation projects where these animals become abundant. The purpose of this paper is to discuss the jack rabbit depredation problems experienced on the Bureau of Land Management's range rehabi1itation projects being conducted in the high sagebrush areas of Eastern California and along with this present the control techniques employed to reduce this depredation on one of these sites. The specific jack rabbit control program under discussion was conducted on the Boggs Crested Wheatgrass Seeding located fifteen miles north of Cedarville, California near the California-Nevada border. At this site a total of 6,000 acres were aerially treated with herbicide to eliminate the sagebrush. Preceding this approximately 1,000 acres of the total parcel was seeded to crested wheatgrass. The site is typical of the areas where range rehabilitation of this type will be conducted in the future; therefore, the jack rabbit control practices employed here should prove quite adaptive to similar sites.

WINTER STARLING CONTROL IN IDAHO, NEVADA, AND OREGON

Homer S. Ford — Mon, 19 Dec 2005 14:55:58 PST

This paper is intended to bring you up-to-date on the progress of various winter starling control projects conducted by our Bureau on feedlots in Idaho, Nevada, and Oregon. This report briefly covers the field work accomplished since that reported by the late Mr. H. Nelson Elliott in his paper delivered to the second meeting of your conference held in Anaheim, California, in March 1964. Prior to the winter of 1960-61 we experienced a tremendous build-up of starling populations in feedlot situations throughout the Pacific Northwest. The expanding livestock feeding industry was receiving great economic losses from starlings eating livestock feed and fouling additional feed and water. Conventional measures such as hazing and shooting were ineffective in protecting the feed yards. It was evident to this Bureau that means and measures had to be found to reduce starling numbers in feedlot situations. Due to starling build-ups an intensive experimental control project under field conditions was undertaken in Idaho in the winter of 1960-61. The experimental research was under the leadership of biologists of the Bureau's Denver Wildlife Research Center. The field operations were made possible through financial participation of the Idaho Cattle Feeders and the Idaho Department of Agriculture. Various control techniques were utilized and a summary of these is contained in Mr. H. Nelson Elliott's presentation to the Second Vertebrate Pest Control Conference. He also reported that the use of thallium sulphate baiting had reduced starling damage in feedlots, but the Bureau did not anticipate registration of thallium for bird control and that further emphasis would be placed on the development of more selective lethal agents.

WINTER STARLING CONTROL WITH DRC-1339

Paul E. Levingston — Fri, 16 Dec 2005 15:04:11 PST

Several years ago starling problems in cattle feed lots exploded to economic proportions. In 1964 one northern California feed lot operator reported a loss of $1,000 per day during the winter months. This resulted from daily activity of over a million starlings. Along with consuming and contaminating large amounts of cattle feed, the birds disturbed the cattle and prevented regular feeding habits. This reduced weight gains drastically. To combat what had become a state-wide problem, in 1962 a cooperative program between the California Department of Agriculture, the county agricultural commissioners, the United States Bureau of Sport Fisheries and Wildlife, and the University of California was put into action. The early work consisted of field trials in feed lots located in Solano, Madera, Merced, and Contra Costa Counties to develop behavioral information and control methods. In northern California, McDougal's feed lot near Collinsvilie, Solano County, was selected as the field trial site. During winter of 1963-1964 the work consisted of bait preference trials and progressed to use of TEPP treated grain baits. This resulted in a calculated kill totaling 4l4,000 starlings. Pilot control programs, under general supervision of the United States Fish and Wildlife Service, Division of Wildlife Services, Bureau of Sport Fisheries and Wildlife, were conducted at McDougal's feed lot during fall and winter of 1966 and 1967. The objective was to reduce the starling population to an economic tolerable number. To achieve this objective it was decided that, weather permitting, it would be necessary to have bait continuously exposed for starling consumption.

THE USE OF LIVE TRAPS TO REMOVE STARLINGS AND PROTECT AGRICULTURAL PRODUCTS IN THE STATE OF WASHINGTON

Vincent Bogatich — Fri, 16 Dec 2005 14:58:37 PST

Much has already been said and written about the use of live traps for the control of starlings in the State of Washington and our efforts have evidently been viewed with interest for we have received letters and questions about our program from all over the world. Our interest in the possibilities of the live trap began back in 1960 when spring and summer surveys revealed a high nesting population and an increasing percentage of bird damage to a very valuable cherry growing industry. This damage was mainly attributable to the local flocks of juvenile starlings. Over the years we have learned much about, the habits and characteristics of the starlings and apply this knowledge to the present day program. Adult birds strive to bring off two broods. The first brood leaves the nest in early May and the second in mid-June. Small flocks of juveniles will then develop in widely scattered areas, usually in irrigated pastures, throughout the county. Even the city reared bird will join its country cousin in these feeding and training areas. These young birds are easily caught and we find that traps located in these communal areas, or along flyways will reduce local populations before cherries become ripe. We also strive to intercept them enroute to the orchards. Traps located in prime nesting areas will take a few adult starlings during April and May, However the catch will pick up significantly as the young leave the nest. Records kept of one man's monthly catches over the years reveal that the average take for the month of May is about 700 starlings and the average for June exceeds 7,000.

THE SUMMER EUROPEAN STARLING PROBLEM IN TULARE COUNTY

William R. Clark — Fri, 16 Dec 2005 14:55:28 PST

Summer starlings (Sturnus vulgaris) are known to have caused damage to the agricultural industry of Tulare County since 1960. At this time the first confirmed appreciable damage to grapes occurred. Since that year the threat has grown considerably as populations have increased. Annual monetary losses have fluctuated but damage has increased steadily and many losses are going unreported or unevaluated by the growers. Known total monetary losses in Tulare County have reached over $28,500.00 in a single summer and the unknown or unrealized losses would probably double this figure. The diversity of crops damaged has mounted steadily, as anticipated, and grapes of various varieties are still the hardest hit, with plums approaching a close parallel. Certain varieties of figs are preyed upon extensively even though they are not the kind predominently grown commercially now in Tulare County. Nectarine, peach, berry, apple, cherry and olive varieties are also affected by this gregarious pest.

STARLING CONTROL IN LIVESTOCK FEEDING AREAS

Richard R. West et al. — Fri, 16 Dec 2005 14:53:19 PST

The Denver Wildlife Research Center has been investigating methods to combat starling (Sturnus vulgaris) problems at livestock feeding areas since 1960. A variety of chemicals, baits, and methods of bait placement have been tested. This paper summarizes these investigations.

CHEMICALS TESTED About 500 chemicals have been screened for toxic and stupefacient effects on starlings. Although several chemicals have been found that immobilize starlings in the laboratory, they have been largely ineffective in the field; most starlings regurgitate the treated baits, and seldom have substantial numbers been affected. Of the toxicants screened, four compounds, TEPP, DRC-632, DRC-1327, and DRC-1339, have shown enough activity as control agents for starlings to warrant intensive investigation in the laboratory and the field.

ROLE OF THE AGRICULTURAL EXTENSION SERVICE IN VERTEBRATE PEST CONTROL

Marvin D. Davis — Wed, 14 Dec 2005 12:16:45 PST

Frankly, I often wonder what our role is in vertebrate pest control. It seems to me that we in A.E.S, are frequently treading in the "twilight zone" of pest control. This is because of the wide diversity of problems which arise within an area such as I represent. I feel it is most significant that our county was invited to cover the role of A.E.S. in vertebrate pest control and discuss the tremendous variations and considerations necessary to serve an urban/semi-urban to rural county. Those of you familiar with San Mateo County readily recognize the potential problems due to population growth, topography, climate and vegetative distribution. I feel the best way to adequately cover this subject is to break our role into three categories with which you are all familiar. These are: research, education, and liaison. I shall cover each of these phases as they relate to typical situations which frequently involve our assistance and services.

BIRDS AND AIRPORTS

Erwin W. Pearson — Wed, 14 Dec 2005 12:00:26 PST

For all practical purposes, research in this country on the problem of bird hazards to aircraft began in 1960 with the crash of an Electra turboprop that carried 62 people to their deaths and was attributed to ingestion of starlings into the engines. In this paper I intend to review the problem and present some of the answers found by investigators in this country and, to lesser extent, abroad. The discussion will be roughly divided into two parts: 1) what: causes the problem, when, and where; and 2) what has been and is being done at airfields to reduce it. Dr. Seubert of the Patuxent Wildlife Research Center described the problem in Europe at this conference 3 years ago, so I will try to bring you up to date on the problem here. We at the Denver Wildlife Research Center have been actively engaged in few specific studies at airfields. Although we mailed a questionnaire to airport managers at 190 installations in the 22 mainland states west of the Mississippi River in 1961 and made follow-up personal visits to 25 commercial and military airfields at seasons of the year when most problems had reportedly occurred, it appeared that none would last long enough for us to undertake studies. Since then we have attempted primarily to solve crop depredation, feed lot, and roost problems with the idea that knowledge obtained from them could be adapted and applied to bird hazard problems as they arose at airfields.

CONTROL OF NUISANCE PESTS IN SUBURBIA

Howard A. Merrill — Wed, 14 Dec 2005 11:58:16 PST

To a rancher or high-rise apartment dweller, problems with vertebrate pests in suburbia may seem insignificant. But when one stops to consider that last year over 2 million acres of farmland were converted into urban and industrial use, then it takes a different perspective. Some mammals are protected—game animals and fur bearers are usually protected by Fish and Game Departments. Cottontail rabbits, deer, and tree squirrels are examples of game animals, and muskrats, foxes, badgers, and raccoons are examples of fur bearers. In California a number of birds and mammals have no protection; these are English sparrows, American or black-billed magpies, crows, California or scrub jays, Steller's or crested jays, starlings, moles, opossums, coyotes, weasels, skunks, cougars, bobcats, and rodents including ground squirrels, rats, mice, gophers, and porcupines. Other birds and mammals may be controlled under varying conditions (see references). For example, blackbirds may be killed when they are committing or about to commit serious depredations upon ornamental or shade trees or agricultural crops. Still others may be killed under supervision of the Agricultural Commissioners or a permit from the Bureau of Sport Fisheries and Wildlife. Some of these classifications vary from state to state, and if you have any doubt about the legality it's best to contact your state fish and game department, the state department of agriculture, or the Bureau of Sport Fisheries and Wildlife.

POPULATION CONTROL OF HERRING GULLS BY THE EMBRYOCIDE, SUDAN BLACK*

David K. Wetherbee — Wed, 14 Dec 2005 11:52:39 PST

The purpose of this experiment was to test the application of a biochemical method proposed to control the hatching of herring gull (Larus argentatus) eggs in a wild population. Sophistication was considered in terms of practicality, effectiveness, selectivity, economy, humaneness, remote application and hazards to and in the environment. The herring gull, which at the turn of the century was unknown as a breeding bird in northeastern United States, now nests abundantly along the Atlantic coast as far south as Virginia. Its phenomenal increase in numbers has resulted in conflicts with several human interests, including competition with other desirable nesting bird species, navigational hazards at airports, and the desecration of coastal property. Northeasterners, however, are by no means blind to the aesthetic and other values of the herring gull and there are few who would tolerate the outright slaughter of the over-population. In order to come to grips with this delicate problem in Massachusetts we reviewed the current knowledge about inhibition of avian reproduction (Wetherbee et _al_., 1962), developed some philosophies of avian biological control (Wetherbee, 1966), discovered the anti-fertility effects of a biological stain, Sudan Black (Wetherbee et a!., 1964), and in 1966 tested the use of this compound in a large-scale ecological experiment on Muskeget Island, Massachusetts.

BLACKBIRD BEHAVIOR

Gordon W. Boudreau — Wed, 14 Dec 2005 11:50:15 PST

A knowledge and understanding of a bird's habits and behavior patterns is prerequisite to any intelligent approach toward solving problems created by that species. This also applies to associated species commonly observed with it. Since my subject today is blackbirds I will confine my observations to species in this group, particularly red-winged blackbirds. The Red-Winged Blackbird, (Agelaius phoeniceus) is numerically and economically the most important. Several sub-species or races are recognized and in California the most important of these is the Bi-colored Blackbird, (A. p. californica). The ranges of subspecies commonly overlap, particularly in the Southeast, and field identification is often difficult. In the central valley of California the Tri-colored Blackbird, (Agelaius tricolor) is responsible for much of the depredation in crops, particularly rice. Another typically western species is the Yellow Headed Blackbird, (Xanthocephalus xanthocephalus) which commonly winters in the Southwest and Mexico. This is a large blackbird easily recognized by the black plumage and yellow head. A common blackbird of the West and North-central States is Brewer's Blackbird. The males are black with yellow eyes while the females are grayish with dark eyes. Grackles, (Quiscalus quiscula), are large shiny blackbirds with a long wedge-shaped tail and are more common in the East. A common associate of all the above species during the fall and winter months is the Brown-headed Cowbird (Molothbus ater). The well-known Starling, (Sturnus vulgaris) is also found associated with all of the above species, particularly in their fall and winter concentrations. Red-wing, grackle, cowbird, and starling combinations comprise many of the enormous winter concentrations in the Southeast. In the Southwest, redwings, yellow-headed, and Brewer's blackbirds commonly associate with cowbirds and starlings during the winter months. These associations are usually dissolved in the spring during the breeding season. All of the above species, plus several more, are often indiscriminately referred to as "blackbirds". Since the habits and behavior patterns differ with each species correct identifications are necessary before a control program is planned, I have frequently recommended control procedures by mail which were unsuccessful because of incorrect identification of the offending species. Starlings and red-wings are often confused and several times control procedures for starlings were recommended when actually only red-wings were involved. In recent years, the starling has achieved considerable notoriety and to many people any dark-colored bird is a starling. It is important that the correct identification of the offending species be established, preferably by direct observation.

BLACKBIRD DAMAGE CONTROL WITH CHEMICAL FRIGHTENING AGENTS

Paul P. Woronecki et al. — Wed, 14 Dec 2005 11:45:49 PST

Birds involved in damage or nuisance situations also have beneficial qualities, and most species are protected by State and Federal laws. Programs designed to alleviate bird problems, particularly those involving blackbirds, should first seek to discourage the birds from using problem areas and not to eliminate populations by direct reductional control. Habitat manipulation and mechanical frightening devices are useful techniques for discouraging bird activity, but certain chemical frightening agents have distinct advantages in some situations. We have found these agents particularly effective when used to control blackbird damage. Chemical frightening agents can be divided into two groups, the lethal and non-lethal. The latter is obviously more desirable, since accidental deaths of upland game, waterfowl, and insectivorous songbirds are minimized. Whether lethal or non-lethal, the success of these agents is largely dependent upon eliciting the desired behavioral response from unaffected birds in the population. The extreme gregariousness of blackbirds makes them ideal subjects for demonstrating the utility of this type of chemical. Personnel of the Denver Wildlife Research Center have been actively searching for and developing safe and effective chemical frightening agents since 1360. Eighty-two potential agents have been screened, but only a few have warranted field testing. Certain substituted phenyl N-methyl carbamates have shown particularly wide safety margins between temporary immobilization and death (Schafer et al., 1967)- One of these, DRC-736, has been field tested extensively and shows special promise for protecting livestock feedlots from problem blackbirds. A second compound, 4-aminopyridine (DRC-1327), described by Goodhue and Baumgartner (1965a, 1965b), has been tested at Sand Lake National Wildlife Refuge, South Dakota, since 1962 (De Grazio, 1964). This chemical frightening agent has been the most successful of the many control methods tested to alleviate blackbird damage to ripening corn.