Individual study: Cross-fostering of whooping crane Grus americana eggs in the nests of sandhill cranes Grus canadensis at Grays Lake National Wildlife Refuge, Idaho, USA
Kuyt E. (1996) Reproductive manipulation in the whooping crane Grus americana. Bird Conservation International, 6, 3-10
Although the whooping crane Grus americana formerly occurred more widely in Canada and the USA, the last wild migratory population breeds in and around Wood Buffalo National Park, on the border of Northwest Territories and Alberta, Canada. Since 1967, 'surplus' eggs from wild clutches with two viable eggs (usually only one chick is successfully fledged) have been collected in order to establish a captive population of the species. As part of a more general review of the management actions taken for the whooping crane between 1967 and 1991, this study documents an attempt to reintroduce the species into the Rocky Mountain region of the USA by cross-fostering eggs in the nests of sandhill cranes Grus canadensis breeding at Grays Lake National Wildlife Refuge (43º03' N, 111º27' W), Idaho.
Between 1975 and 1988, 288 whooping crane eggs were introduced into preselected nests of sandhill cranes breeding in Gray Lakes National Wildlife Refuge. Of these, 215 had been collected from the wild population at Wood Buffalo National Park, and (from 1976 to 1984) 73 captive-produced eggs were also sourced from Patuxent Wildlife Research Center in Maryland*. Although the viability of eggs was not tested in the early years of the programme, diagnostic viability tests were subsequently introduced.
In addition, nine translocated whooping cranes were also released at Grays Lakes during 1986-1988, in an attempt to enhance opportunities for pair formation.
Overall, 73% (210 of 288) of cross-fostered whooping crane eggs hatched successfully, with the hatching success of wild-sourced eggs (77%) higher than that of captive-produced eggs (60%). The main causes of egg failure were predation (particularly by coyotes Canis latrans) and infertility or embryonic death. There were 47 cases of chick mortality, most of which occurred before birds were 30 days old. Predation (by coyotes and red fox Vulpes vulpes) and bad weather were the principal causes of mortality in young cranes. Of 85 cranes that fledged successfully, only 13 (15%) were still alive in 1991. Where causes of mortality were known (27 instances), they included collision with powerlines (40%), fences (22%), disease (18%) and predation by birds (7%). No permanent pairs formed among surviving birds, possibly because of their low density or problems with imprinting on their sandhill crane foster parents. Only one of the nine translocated individuals released during 1986–1988 returned to Grays Lake in subsequent years.
* For further details, see
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