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The U.S. Congress passed the Endangered Species Act in 1973. Since then, more than 910 animal and plant species worldwide have been listed as threatened or endangered by the U.S. Fish and Wildlife Service. Of these, 410 occur in the United States or its territories. The famed Red Data Books, published by the International Union for the Conservation of Nature and Natural Resources (IUCN), list about 840 animal species and subspecies worldwide as endangered.
Soulé (1986) has suggested that about 1,500 nonfish vertebrate species are likely to become extinct by the year 2050. Inclusion of fish will likely double this number. This implies a growing extinction rate of 10 to 30 vertebrate species per year without consideration of subspecies and populations.
Current guidelines from population biologists indicate that it is desirable to maintain captive populations of 100 to 300 individuals of a species (depending upon the number of founders, i.e., individuals whose offspring form captive populations, and generation time), if it is to be viable and if it is to retain about 80 to 90% of its genetic diversity for 100 to 200 years (Frankel and Soulé, 1981; Rails and Ballou, 1986). These numbers suggest that if all institutional spaces for mammals and birds were used for Species Survival Plan (SSP) programs, then only about 300 birds and mammal species could be managed in North American institutions. This is less than 10% of the number of species now exhibited in North America. Expansion of the programs to fill all the space in all the world’s potentially cooperating exhibit institutions might increase the number to about 900 species. This is 20 to 25% of the number of species exhibited. Thus there is pressure to increase the efficiency of captive management programs and to find alternative means for captive preservation of genetic resources.
Prepared diets, carefully tuned to the needs of particular groups of species, are available as commercial products, greatly reducing the variations inherent in local supply and introduced by individual preparers. Now attention is directed to special requirements of individual or particular collections, for example, to thwart reproductive failure or failure of neonates to thrive or survive and to meet the special needs of hand-reared animals.
Remotely administered chemical immobilization of captive and free-ranging animals is a major innovation that has revolutionized our ability to work with wild animals and has become acceptably safe for routine use by experienced personnel (Harthoorn, 1976). Animals can be captured in the wild for treatment, relocation, data collection, and fitting of radio collars (Mech et al., 1984). Modern delivery techniques range from dart guns to blow pipes. The most widely used drugs in