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using young animals which have become separated from their mothers, e.g., Cali- fornia sea otter (Enhydra lutris) pups sometimes wash ashore. If the program is begun before the wild population has reached the "crisis" stage, it is wise to begin with the capture of a few wild individuals (or the capture of some wild individuals belonging to a closely related "model" taxon) to enable the de- velopment of suitable husbandry techniques. There are many taxa, for example, kangaroo rats (Dipodomys), that zoos do not know how to breed reliably in captivity. In such cases, research on genetics, behavior, nutrition, disease or reproduction may be necessary to find the reasons for the lack of breeding success, and research takes time. In the case of the tamarin, the husbandry problems concerned both behavior and nutrition (Kleiman et al. 1986). Once they were solved, in the mid-1970s, the captive population grew rapidly (Figure 2). Initial problems in maintaining and breeding the ferret population involved disease and reproductive synchronization of the males and females during the short breeding season; they were overcome by 1989 (Thorne and Oakleaf 1991). Siberian polecats (Mustela putorius) and domestic ferrets (Mustela putorius furo) were used as surrogates for ferrets during the breeding season and for research on reproductive biology (Wildt et al. 1989). Both rails and condors bred fairly well in captivity from the start, because zoos had experience with these or closely related species (Derrickson 1987, Wallace in press). General goals and overall planning. Genetic goals for captive populations are specified in terms of the proportion of genetic variation (expressed as heterozygosity) to be maintained and the length of time for which it is to be maintained. The proportion of genetic variation retained within a closed population depends upon the population's effective size and the number of generations for which it remains closed. The effective size of a population can be defined as the size of an ideal population (a hypothetical population with specific properties central to population genetics theory-see Fal- coner 1981, Hedrick 1985) that would have the same rate of loss of heterozygosity as the actual population under consideration. The effective population size generally is only a fraction of the actual population size (Laude and Barrowclough 1987). Generation length is critical because some genetic variation is lost when the parent generation passes its genetic variation on to the next generation (an offspring contains only half the genetic material present in each of its parents). Thus, the longer the generation time of a species, the smaller the proportion of genetic variation that will be lost during a given time period (Soule et al. 1986). A general goal for captive populations is the maintenance of 90 percent of the genetic variation present in the source (wild) population for 200 years (Soule et al. 1986). The panel of experts that made this recommendation concluded that "the 90 percent threshold represents, intuitively, the zone between a potentially damaging and a tolerable loss of heterozygosity" and that two hundred years was an arbitrary but "reasonably conservative" planning time-frame (Soule et al. 1986). Goals for the tamarin, rail, ferret and condor programs are compared in Table 2. The tamarin program has adopted the -90 percent for 200 years" goal. We also have shown this goal for the condor program, although the USFWS has not yet adopted an official goal. The ferret and rail programs are using the goal of -90 percent for 50 years." Planning for a shorter time period was deemed appropriate in these cases due to the short generation times for these species (see Table 2) and plans for the rapid re-establishment of several wild populations (Ballou and Oakleaf 268 ? Trans. 571h N. A. Wildl. & Nat. Res. Conf. (1992)