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..-s:.... 37 number of eggs available for transplanting resulted in a relatively small population which peaked at 33 individuals in winter 1985, The'sex ratio was equal at fledging age among 22 cranes examined at WBNP and 6 cranes at GL. The data, based on chromosome identification in the blood, suggests that differential mortality rates are the basis for unequal sex ratios among adults in the RMP. In June 1981, a captive, 3-year-old, parent-reared female whooping crane was transferred from PWRC to GL and placed on a wild male's territory (Drewien 1982, Unpubl, Prog. Rept. No, 17, Whooping Crane Transplant Experiment, Idaho Coop. Wildl. Res. Unit, Univ. of Idaho, Moscow: pp. 32-41). This experimental reintroduction was attempted to determine if it was possible to simultaneously augment the wild cross-fostered population, rectify the male-skewed sex ratio, and hasten the onset of breeding in the wild population, It was assumed that the probability of pair-formation would be relatively high for several reasons, including: (1) released birds are initially subordinate to wild birds following release, a situation favoring male dominance and pairing; (2) the male at GL was sexually mature, and the female was old enough for pairing; and (3) numerous instances have been documented in which wild cranes have successfully paired with tame or captive individuals (Hyde 1968, Longley 1970, Nesbitt 1979). Previous experiments with sandhill cranes demonstrated that the transition period from captivity to the wild inv.olved considerable learning and consequently occurred over a relatively extended period, In this particular release, it was assumed that this transition period would be ameliorated and shortened because if the two. paired her mate would introduce her to foods, foraging methods, roosting areas, teach a proper response to potential predators, and ensure proper migration by the female. Although the female rapidly adjusted to the wild and associated periodically with the male, a pair bond was never established. Successful migration by the unattached female seemed unlikely, therefore she was recaptured and returned to PWRC in October (Drewien and Clegg 1992), This experiment was repeated the following summer, In 1982, as in 1981, the female readily adapted to the wild environment, and her presence stimulated increased territorial activities:by the male (Drewien 1983, Unpubl. Prog. Rept. No. 18, Whooping Crane Transplant Experiment, Idaho Coop. Wildl. Res. Unit, Univ. of Idaho, Moscow: pp, 8-10). Unfortunately, the experiment was terminated early when the male died after becoming entangled in a barbed wire fence on his territory. Again, the female was recaptured and returned to PWRC. The experiment was repeated in 1989, but earlier in the season (May) than the 1981 and 1982 attempts (June). A captive six-year-old female from PWRC was placed in a pen on a wild male's territory at GL. The male exhibited much interest in the female and after 1 week she was released from the pen. Considerable pair formation behavior occurred between the two birds including unison calling and copulations. No nesting attempt was made, perhaps because it was somewhat late in the season. The male molted his flight feathers and secluded himself in the marsh. In early June the female abandoned the flightless male but was joined by another wild male.