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'.' ,., 13 are diurnal migrants and make regular stops to feed and rest. Although whooping cranes will use a variety of habitats for foraging and roosting during these stopovers (Armbruster 1990, Lingle ~ ai, 1991 I, they seem to prefer isolated sites away from human activities, This preference and the birds' rarity, result in few authenticated sightings during migration each year. For almost half of the year, whooping cranes occupy winter quarters on and adjacent to Aransas NWR. Although close association with other whooping cranes is tolerated at times on the wintering grounds, pairs and family groups typically occupy and defend relatively discrete territories. Recent studies indicate a declining territory size as the population increases, The recent average is 117 ha (Stehn and Johnson 1987), Subadult and unpaired-adult whooping cranes form small flocks and use areas outside occupied territories (Blankinship 1976, Bishop and Blankinship 1982). Subadults tend to winter near the territories where they spent their first year (Bishop 1984). Paired cranes will often locate their first winter territory near the winter territory of one of their parents (Bishop 1984, Stehn and Johnson 1987). Animal foods-especially blue crabs ICallinectes saDidus), clams (Taaelus Dlebius, Ensis !!lilJ.Qr, Ranaia cuneata, CvrtoDleura costada, Phacoides Dectinata, Macoma constricta), and the plant wolfberry ILvcium carolinianuml predominate in the winter diet (Allen 1952, 1956, Uhler and Locke 1l'l70, Blankinship 1976). Most foraging occurs in the brackish bays, marshes, and salt flats lying between the mainland and barrier islands. Occasionally, they fly to upland sites when attracted by foods such as acorns (Quercus virainianal, snails, crayfish and insects, and then return to the marshes to roost. Uplands are particularly attractive when partially flooded by rainfall, burned to reduce plant cover or when food is less available in the salt flats and marshes (Bishop and Blankinship 1982). Some whooping cranes use upland sites frequently in most years but agricultural croplands adjacent to the Aransas NWR are rarely visited, High fall tides and heavy rains sometimes flood tidal flats. In these circumstances, the birds forage almost exclusively on blue crabs and wolfberry in flooded areas, In December and January, tidal flats typically drain as a result of lower tides, and the birds move into shallow bays and channels to forage primarily on clams, although blue crabs are occasionally captured while probing the bottom. Clams are a significant dietary item when water depths are low, temperatures cold, and during drought when high salinity reduces the blue crab population, Most clams and small blue crabs (5 em or less in width) are swallowed whole, Larger crabs are pecked into pieces before being swallowed (Blankinship 1976). As spring approaches, dancing, unison calling (Archibald 1976), and flying increase in frequency, and are especially indicative of pre-migratory restlessness (Allen 1952, Blankinship 1976): Family groups and pairs are usually among the first to depart wintering grounds, assisted by strong southeast winds which typically occur at this time of year. First departure dates normally occur between March 25 and April 15, with the last birds usually leaving by May 1. Occasional stragglers may, however, linger into mid-May, and in 16 years in the period 1938-1992, one to 4 birds (27 birds total) have remained at Aransas NWR throughout the summer. Some of these birds were ill or crippled or mates of birds which were crippled.