Organizing for Endangered and Threatened Species Habitat

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? ? ? - and their summer nesting grounds in Wood Buffalo National Park, Canada (Currier, Lingle, and ? Walker 1985, p. 22). This central Nebraska patch has been called the waist of a habitat ? hourglass; millions of birds depend on the few resources available. Weeks later the several ? migrating species spread out over wide ranging sparsely populated northern breeding grounds. - But, in the narrow stretch of central Platte, the many migrating species including the sandhills - and the few whoopers become concentrated in the late February-April period in a manner that occurs at no other time (Grooms 1991: 116). ? ? In early spring along the Gulf Coast, Southwest and northern Mexico, sandhill cranes . begin calling and gathering together for the annual migration north (Figure 3). Whoopers fly in - pairs and singly. Both sandhill -and whooping cranes fly in daylight, relying on thermal updrafts to improve efficiency and minimize energy expenditures. Riding an updraft and then gliding ? northward, they steadily lose altitude until the next thermal lifts them and they repeat the process. ? Often flying a mile above the earth, they can soar to 20,000 feet above sea level. They arrive at a ? staging area along the Platte river by late February and early March, descending from cold wintry . skies into sandhill country, with rolling hills and marshes, oxbows and shallow lakes, close to brown harvested cornfields. Wide expanses of shallow water offer protection from predators that ? have to make long running splashing attacks. ? ?_? - Stopping along the Platte to replenish reserves and add fat, whooping cranes tend to • arrive a bit later, and use the area less extensively, than the sandhills who begin to arrive in late February and depart by mid-April for the last push, following the spring thaw north to summer ? breeding grounds. Arriving in the sub- and arctic region, especially just south of the Great Slave ? Lake of the Canadian Northwest Territory in Northern Alberta's Wood Buffalo National Park, - whooping cranes build a platform nest of rushes, and raise one or two young each year. Whooping cranes mate for life, and vigorously defend their territories in both summer and ? wintering grounds (Allen, 1969). There is seldom a break in the fierce alertness in resisting ? intrusion of any other whooping crane pair. Most whoopers leave their northern breeding grounds • by the end of September but often do not arrive at their gulf coast wintering grounds until . December. Pairs with newly-fledged juveniles typically are the last to return. They also display much solidarity in the simple family unit protecting and nurturing fledglings until the young's ? first spring, at which time the adolescent birds are driven from the family group with jabs and ? lunges before the mating pairs lift off again for the long migration north leaving the newly ? independent yearlings to migrate singly in their wake. The central Platte in the Big Bend area of Nebraska is made up of alluvial bottom lands, river terraces, and gently rolling bluffs along the river escarpment. Bottom lands are flat and extend for up to 15 miles on both sides of the river channel. R.ich prairie soils support a productive agriculture. Each year, this area provides for the needs of millions of migratory birds-cranes, ducks, and geese. The few whooping cranes, and almost a half million sandhills, make good use of harvested corn and alfalfa fields, grassland, and unvegetated river sandbars. They feed on cropland grain, obtain invertebrate (e.g. snails and earthworms) food from alfalfa fields and wetland-grasslands. Wet meadows provide both food and areas for courtship rituals. Both whoopers and sandhills come to the central Platte because it is the only locale in mid- continent that meets all their requirements (Currier, Lingle, and Walker 1985: 7): 11