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..~' 46 3. Promoting adoption of captive-reared whoqping crane chicks by wild adults established in an area through cross-fostering '1:0 sandhill cranes. The adoption process would add to the wild population a group of w~ooping cranes without the improper . imprinting problems. The young birds, hopefullY, will learn migratory and survival techniques from their adoptive parents. This approach has been termed the guide bird technique. The Grays Lake cross-fostering experiment successfully produced wild whooping cranes capable of migrating and surviving in a challenging environment. However, because these cranes did not pair, and have experienced excessively high mortality, a technique for reestablishing a self-sustaining migratory population is lacking. A potential solution would be to use cross-fostered whooping cranes as guide birds to introduce young captive- produced whooping crane chicks into the wild. Members of the Canadian Whooping Crane Recovery Team in 1992 suggested the guide bird experiment as an appropriate use of the birds surviving in the RMP. Such an experiment would test one technique which might be used to establish another migratory population in Canada late this century. The young whoopers, reared by adults of their own species, might learn to. survive in the wild and follow a predetermined migration route in the Rocky Mountains. Being reared by conspecifics, they would be sexually imprinted on their own species. Ten adult whooping cranes survive in the RMP, including 4 females. Males range in age from 8 to 16 years and females from 8 to 12 years. Six of these whooping cranes winter annually at Bosque del Apache NWR and 2 at state game management areas north of the refuge. Three captive-reared chicks were released into the population in the guide bird experiment in fall 1993 and one survived in the winter of 1993-1994 in New Mexico. , The cross-fostered cranes have exhibited various parental behaviors on summer territories at GL and in a pen nearby. Solitary territorial males have helped neighboring sandhill crane pairs raise young, including protecting, feeding and brooding them. Several males have built nests. One male intermittently incubated an empty;nest and a sandhill crane egg placed in this nest. In 1988, 2 male whoopers assisted a sandhill crane foster-parent pair raise a whooping crane chick. Male and female whoopers associated with, fed and temporarily reared sandhill crane chicks in the pen during 1990491. These activities and chick adoptions at the United States captive facilities, sUQgest that some cross-fostered whooping cranes might adopt or bond with and rear a whooping crane chick. Such bonding experiments will occur in pens with wild-captured a\:lults and on the spring territory of free- living wild birds. These experiments began in 19931 and will continue in 1994, Four to six whooping crane chicks are planned for use in this rl!search each year. The completion of the 2-year project will provide another decision point about future efforts in the Rocky Mountains, and an opportunity for review and recommendations by all interested parties. The other techniques for reintroducing a migratory population should be tested in the Rocky Mountains or at other geographic locations. , As part of the guide bird experiment, the Service is 'proposing to designate the RMP .as experimental nonessential. The "experimental" designation increases the flexibility of the Service and other land management agencies to manage reintroduced populations because they can be treated as threatened species rather than endangered. The Service has more discretion in devising management programs for threatened species than for endangered