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36 <br />Non-riverine roost sites are a:Lso occupied by whooping cranes <br />throughout the migration corridor (Howe 1987). Although the use <br />of such sites has not been obsE:rved within 3.5 miles ot the <br />Platte River, characteristics of some non-riverine sites are <br />described by Ward and Anderson (1987) and Shenk and Armbruster <br />(1986). Characteristics common to non-riverine roost sites <br />described by Ward and Anderson (1987) include: <br />(1) Mean unobstructed visibil'ity of 330 to 3300 feet; <br />(2) Distance to nearest active road ranged from 2000 to <br /> 9000 feet; <br />(3) Distance to occupied home sites ranged from 820 to 9000 <br /> feet; <br />(4) Bottom substrate was mud; <br />(5) The wetlands were classified as either lacustrine or <br /> palustrine. <br />B. ForaQinQ <br />Some whooping cranes in the Aransas-Wood Buffalo flock occupy the <br />Platte River during spring.and fall migrations (Tables 3& 4). <br />Whooping cranes feed in a variety of habitats i:n the Platte River <br />valley including cropland, wet meadows, palustrine wetlands, -and <br />native grassland (USFWS.1981, Lingle et al. in press;.NGPC, <br />unpubl. data. In the spring, wetlands along the Platte River and <br />elsewhere along the migration .route provide whooping cranes the <br />opportunity to abtain.food items that are essential for survival <br />and successful reproduction (USFWS 1987a). Foraging sites <br />generally are associated with sites near nocturnal roosts (USFWS <br />1987a). Whooping cranes use both plant and animal foods during <br />their migrations. Known animal foods include insects (Swenk <br />1933, Allen 1952), fish (Allen 1952, Lahrman 1976), amphibians <br />(frogs and salamanders), crayfish, earthworms and snakes (U5FW5 <br />1987a). Known plant items consumed include corn, wheat, sedges, <br />and grasses (Allen 1952)r The foraging ecology of whooping cranes on migration is not well <br />known. A reliable and abtindant invertebrate food"source provided <br />by wet meadows is an important aspect of the spring migration. <br />ecology of whooping cranes (USFWS 1987a). Because snow and ice <br />are still present at the time of arrival on the breeding grounds, <br />many foods are not readily available which requires the birds to <br />rely on stored energy and nutrients to survive until the <br />emergence of resident food items (USFWS. 1987a). It is not known <br />whether nutrients acquired during migration are essential for <br />successful reproduction, or if the essential nutrients are <br />obtained on the wintering grou.nds.