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12 <br />breeding territory. To date, the minimum distance recorded between nests has been 600m <br />(Kuyt pars. comm., 1991). <br />Eggs are normally laid in late April to mid May, and hatching occurs about 1 month later. <br />The incubation period is from 29 to 31 days. Kuyt (1981jb:126) reported that "Among 6(20�3 <br />clutches observed between 1966 and 1980, 184 (90.6 percent) contained 2 eggs, <br />percent) only 1 egg, and 3 0.5 percent) 3 eggs." Eggs are light -brown or olive -buff overlaid <br />with dark, purplish -brown blotches concentrated primarily at the blunt end. Eggs average <br />100 mm in length and 63 mm in width (Bent 1926, Allen 1952, Stephenson and Smart <br />1972). Whooping cranes may renest if their first clutch is destroyed or lost before <br />mid - incubation (Erickson and Derrickson 1981, Derrickson and Carpenter 1981, Kuyt <br />19810. Whooping cranes generally nest annually, but occasional pairs skip a nesting <br />season for no apparent reason. When nesting habitat conditions are unsuitable, some pairs <br />do not attempt to nest. <br />nt <br />Whooping crane egg and tissue specimens examined for pesticide those encountered at tatu en most <br />Wildlife Research Center have shown concentrations f <br />other migratory birds (Robinson at al. 1965, Lamont and Reichel 1970, Anderson and <br />Kreitzer 1971, Lewis at al. 1992). To date there is no evidence that pesticide <br />contamination has affected the welfare of whooping cranes. <br />Except for brief intervals, one member of the pair remains on the nest at all times. Parents <br />share incubation and brood - rearing duties. Females tend to incubate at night (Allen 1952, <br />Walkinshaw 1965, 1973) and take the primary role in feeding and caring for the young <br />(Blankinship 1976). Parents and young return are brooded by their parentshwhereve� hey <br />days after hatching. After that time, young <br />are when night or foul weather overtakes them. During the first 20 days after hatching, <br />families generally remain within 1.8 km of the nest site (Kuyt pars. comm.). <br />Whooping cranes are omnivorous (Walkinshaw 1973), probing the soil subsurface with their <br />bills and taking foods from the soil surface vegetation. hair feeding until they separate their <br />the <br />parents and gradually become more independent <br />parents preceding the next breeding season. s foods <br />and include <br />(Allene1956,hNovakowski <br />forms of insects, frogs, rodents, small birds, minnows, <br />1966). Foods utilized during migration are poorly documented but include frogs, fish, plant <br />tubers, crayfish, insects, and waste grains in harvested fields. <br />Autumn migration normally begins in mid - September, with most birds arriving on the <br />wintering grounds between late- October and mid - November. Occasionally, stragglers may <br />not arrive until late- December. Nonbreeders and unsuccessful breeders probably initiate and <br />complete fall migration sooner than family groups because young -of- the -year are rarely <br />observed among the first birds arriving in southern Saskatchewan or Texas (Allen 1952, <br />Archibald at al. 1976, Stephen 1979). <br />Whooping cranes are less gregarious than sandhill cranes, and n of normally migrate cranes. a single, <br />pair, family group, or in small flocks, sometimes in the company <br />of up to 10 subadult whooping cranes a during adio tracking studies (Kuyt 1992). They <br />stopovers (staging areas) in Saskatchewan <br />