National Geographic : 1979 May
mate for life, and breeding pairs return each spring to traditional nesting territories. Their eggs, similar in size and appearance, are usually laid in clutches of two; incuba tion periods of about thirty days produce look-alike chicks that remain with their par ents for nine to ten months after hatching. By cautious experiment in 1970 I learned that the sandhills at Grays Lake would not abandon their nests if I switched or removed an egg. Meanwhile, Canadian Wildlife Ser vice biologist Ernie Kuyt was finding whooping cranes equally tolerant. Under Ernie's direction, air searches at Wood Buffalo recorded the spring arrival of the whoopers, the location of breeding pairs, their approximate laying and hatching dates, and the size of their clutches. In 1967 these observations enabled Ernie to begin collecting whooper eggs for breeding. Studies by Dr. Ray Erickson and his staff of the U. S. Fish and Wildlife Service had suggested earlier that whooping cranes would not desert the nest if one of their eggs was removed; indeed, successful rearing of twin young is a rarity. Acting on this, Ernie picked up six eggs at Wood Buffalo for transfer by jet to Ray, who is an assistant director at the Patuxent Wildlife Research Center in Laurel, Maryland. The center's captive flock of 22 whoopers now includes 15 hatched from Canadian eggs. Egg Removal Aids Chick Survival As Ray had predicted, collecting the eggs did not imperil the Wood Buffalo flock. In fact, the number of wild chicks reaching maturity was higher during years when eggs were removed. The operation was repeated, and in 1975 Ernie prepared for the sixth egg transfer in nine nesting seasons, this time to Grays Lake. .f . ""s/"