Identification of the location of the summer breeding grounds of the whooping cranes at Wood Buffalo National Park in 1954 allowed more detailed study of their reproductive habits in the wild, and led to the observation that while many breeding pairs laid two eggs, both chicks would almost never survive to fledge. It was concluded that the removal of a single egg from a two-egg clutch should still leave a single hatchling most likely to survive, while providing an individual for captive breeding. Such removals in alternating years showed no decline in the reproductive success of the wild cranes. The withdrawn eggs were transferred to the Patuxent Wildlife Research Center in Maryland, where approaches for hatching and rearing crane chicks in captivity had been optimized using the more-numerous sandhill cranes. Initial challenges getting the resultant birds to reproduce, even using artificial insemination approaches, would give impetus to the first, unsuccessful attempt at reintroduction, by swapping whooping crane eggs into the nests of the more numerous sandhill cranes as a way to establish a backup population.