Chemical Inhibitors of Ovulation in the Pigeon

The recent increase in the numbers of several species of native blackbirds as well as the increasing concern over the numbers of such exotic birds as starlings (Sturnus vulgaris), house sparrows (Passer domesticus), and pigeons (Columba livia) has prompted widespread study of control methods. This paper reports the results of a 4-year search for a practical oral contraceptive for nuisance birds. Most substances found effective in inhibiting ovulation in other animals proved to have little effect on pigeons, even in nearly lethal doses. Compounds used included: tranquilizers, gametocides, antithyroid compounds, hypophyseal inhibitors, insecticides, fungicides, and coccidiostats. Only provera at 0.1 percent or more in the diet and arasan at 0.35 percent inhibited ovulation without severe debilitation of the birds; the effect was lost as soon as the materials were withdrawn from the diets. Practical results were obtained with the anticholesterol compound SC-12937 (22, 25-diazacholestanol dihydrochloride). When this compound constituted 0.1 percent of the diet for 10 days in early November, no eggs were laid for 3 months, full fertility among some birds was not reached for 6 months, and some remained anovulatory for 12 months. Following spring feeding, ovulation was almost completely inhibited for 3 months, and after 6 months remained 75 percent inhibited. As man expands his numbers he comes in conflict with the few species of animals that are adaptable enough to thrive and even increase despite alteration of their environment or sometimes as a result of a new environment artificially created for them. The coyote's (Canis latrans) spread eastward over half the United States and the tremendous increase in blackbirds are examples of problems caused by species that seem to have profited by man's alteration of habitat. The gradual spread of exotic birds such as the house sparrow, European starling, and domestic pigeon is obviously the result of man's providing food and nesting sites. Each of these birds occasionally becomes so abundant as to require control; and the problems caused by excess feral animals are usually relegated to the field of wildlife management, whether or not we welcome them. The use of poisons to eliminate nuisance birds has many repugnant if not hazardous aspects, particularly in cities. It is opposed by well-organized groups and, in any case, simply makes room for more birds to move in and occupy the same territories. The employment of a multitude of frightening devices from noisemakers and artificial owls to such witch doctory as "little black boxes" and "silvered ropes" serves only to move bird concentrations from one building to another. A new approach seems necessary. Successful control of the screwworm fly (Callitroga hominivorax) in Florida by releasing sterile males (Bushland and Hopkins 1951, Simpson 1958, Knipling 1960) prompted my attempt to find a means of inhibiting reproduction in birds. With avian populations it is neither desirable nor practical to attempt to swamp out normal fertile males by releasing sufficient numbers of hand-reared, infertile male birds. Therefore, leads were sought in the medical literature devoted to birth control through inhibition of ovulation, in poultry literature dealing with side effects of drugs used in control of poultry diseases, in cancer research sidelines (gametocides, mutagens, or cytotoxins), and in wildlife sources revealing effects of insecticides and fungicides on reproduction in birds. 1A contribution from the Missouri Cooperative Wildlife Research Unit: U. S. Bureau of Sport Fisheries and Wildlife, Wildlife Management Institute, Missouri Conservation Commission, and the University of Missouri, cooperating.