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At the Denver Wildlife Research Center our people are actively searching for means of controlling damage by a whole host of animal and bird species. I say controlling damage rather than controlling species because this should be the primary objective. If we can do this without lethal control, so much the better, and it may be the more lasting solution in the long run. Often removal of some animals by lethal means either increases reproduction, survival, or invasion unless complete control is exercised over sufficiently large areas. In spite of these problems, population reduction is often relied on as a means of controlling damage. And where lethal control is required, there is a definite need for continued improvement in agents and techniques of application. In research we must explore all approaches; one such is anti-fertility agents. The principle here is that reproduction is the mainspring that overcomes all mortality factors. Logically, it appears that suppressing reproduction may be a very direct approach in control. We are working on this in both coyotes and rodents, but there is much to learn. For example, we must determine the complete reproductive picture in each target species to know where to attack reproduction. Second, we must find the best agents and how to effectively apply them. Third, we must be able to determine results and how populations respond. This has been the most difficult phase to date. We have not started this work in birds, but our sister laboratory for Eastern United States at Patuxent, Md. has. Antifertility agents are only one promising area. Another, heavily emphasized in the past is chemical agents, particularly toxicants. There are always inherent problems associated with chemicals in control. It isn't enough to prove that a given chemical will work in control; the safety of the handler, primary and secondary hazards, residues, and degredation products if any, also have to be thoroughly investigated. It still provides a productive area, but the time lag in putting it to application is increasing greatly. We have hopes though after finding two highly selective toxicants that more can be discovered. These studies can be approached in two ways, one is the empirical approach, used in the past, of screening numbers of chemicals known or unknown. A newer approach is to first look at the behavior and physiology of the target species to identify the most vulnerable points in their makeup and then search for an agent or technique to interfere or block this action. We are involved in both. Studies have been initiated in the physiology of starlings and redwings to determine first the normal functions and to search for potential areas of attack. This is already opening up new leads that will soon be reported in the literature. One area of promise is using physiological measurements to evaluate fright producing stimuli in birds. Our avian physiologist, Dr. Thompson, is well along in these studies and by telemetering heart rate is able to quantitatively measure responses. This has important implications in being able to determine the most effective sound, chemical, or technique. Another important area to speed up our understanding of damage problems and to be able to more accurately evaluate control methods is through electronics,--principally using telemetry to determine the behavior and movement of offending species and finally to evaluate control. Several of our projects have used this effectively by instrumenting certain rodents before a control trial and determining mortality and survivors afterwards.