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The Application of Chemical Vasectomy Agents to Control
Populations of Wildlife

BOB R. STEWART

Terrestrial and Aquatic Environmental Managers, P.O. Box 2647,
Melville, SK SOA 2PO, Canada


Predation has been identified as a major limiting factor to waterfowl production on the prairies. The source of the impact comes from a number of terrestrial species including foxes, skunks, and raccoons, and predators, principally American crows. These wildlife are most effective at disrupting nesting by depredating the eggs at the nest and to a lesser extent the hen. The problem with management of the predator lies with the fact that waterfowl are but one of a number of prey species which sustain the predator, but one to which attention is largely focused during the nesting period. The problem is compounded by land development activities over the past three decades which have fragmented the nesting habitat resulting in highly efficient searching patterns by the predator. The capacity of the predators to limit reproduction is so large as to overwhelm the ability of the waterfowl to escape their impact until habitat restoration reaches some undetermined level. In the interim, a serious predator pit exists which threatens the success of habitat programs. In the absence of population growth, select species of waterfowl may be held below the critical mass to allow them to escape the threshold of the predator removal.

Many predator control programs including predator fencing and direct predator removal have demonstrated that control of the predator results in significant increases in waterfowl production. However, the limited scope and expense of a fencing program and public criticism of removal programs limit the opportunity to effectively limit predator impacts. Research with reproductive inhibitors to limit the reproductive capacity of problem wildlife appear to be the most promising management strategy. Predator population turnover is rapid and reduction of breeding effort in any single year would dramatically decrease the extent of predation. To be acceptable as a management tool, the reproductive inhibitor should temporarily inhibit reproduction and be target-specific. TAEM has conducted laboratory and field research on snowshoe hares with a chemical which simulated an action comparable to vasectomization of the male, thereby reducing fertilization of the female. The method is particularly attractive for inducted ovulators as breeding with sterile males may result in pseudopregnancy. Target specificity may be attained by development of baits which use the scent of estrous females rather than food as the attractant. Further advantages of baiting systems include the opportunity to include an oral vaccine with the bait. Public opposition to such programs will be limited by the fact that the chemical is not toxic and its effect results only in a temporary reduction of spermatogenesis.

Prior to implementation, detailed information on species, specific dosage rates, timing of efficacy, and modes of delivery must be determined.


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