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Welcome to BNA Online, the leading source of life history information for North American breeding birds. This free, courtesy preview is just the first of 14 articles that provide detailed life history information including Distribution, Migration, Habitat, Food Habits, Sounds, Behavior and Breeding. Written by acknowledged experts on each species, there is also a comprehensive bibliography of published research on the species.
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Nature Of Migration In The Species
Choice of migration routes, nesting locations, and wintering sites is learned rather than innate. Migratory and nonmigratory populations existed historically; there were several migration routes in nineteenth century. Most important were from Louisiana wintering grounds to nesting grounds in Illinois, Iowa, Minnesota, N. Dakota, and Manitoba; likewise from Texas and the Rio Grande Delta region of Mexico to nesting grounds in N. Dakota, Canadian Prairie Provinces, and Northwest Territories (Allen 1952). Species probably regularly traveled the same route as Sandhill Crane through w. Texas to wintering areas in central intermountain region of Mexico (Allen 1952). Another migration route crossed Appalachian Mtns. to Atlantic Coast of New Jersey, S. Carolina, and river deltas farther south. These birds probably nested near Hudson Bay. Coastal Louisiana supported both a nonmigratory flock and wintering migrants (Allen 1952); last member of the nonmigratory population was removed from the wild in 1949.
Timing And Routes Of Migration
Spring migration by Aransas/Wood Buffalo population from Texas Gulf Coast begins 25 Mar to 15 Apr, with last birds generally leaving by 1 May. Family groups and pairs depart first, with experienced breeders among the first to arrive in Canadian nesting area in late Apr. Occasional stragglers may linger at winter area until mid-May, even throughout summer. Subadults arrive last in nesting area, and a few summer in Saskatchewan or other areas south of nesting grounds. Southward migration requires up to 50 d: a 2-d flight from breeding range to staging area in Saskatchewan where birds remain 1–5 wk on grainfields and wetlands, and a rapid 1-wk trip across U.S. prairie states. Spring migration for experienced pairs requires as few as 10–11 d; more leisurely for subadults, although spring daily flights generally cover greater distances than fall daily flights (Kuyt 1992).
Fall migration by yearlings and subadults begins mid-Sep; family groups and paired adults start in early Oct. Most birds spend several weeks resting and feeding in s. Saskatchewan before moving quickly through U.S. Nonbreeders and unsuccessful breeders probably initiate and complete fall migration sooner than family groups because young of the year are rarely observed among the first birds arriving in s. Saskatchewan or Texas (Allen 1952). Birds arrive on wintering grounds late Oct to mid-Nov, occasional stragglers as late as early Jan.
Similar migration pathway is followed spring and fall. From nesting grounds, it extends 4,000 km south-southeast through ne. Alberta, s.-central Saskatchewan, ne. Montana, w. North Dakota and South Dakota, central Nebraska and Kansas, w.-central Oklahoma, and e.-central Texas (Howe 1989, Kuyt 1992). Occasional sightings, however, are reported in adjacent states and provinces. Migration corridor varies from 80 to 300 km wide; roughly parallels the 1,000-m contour line between Mexico and Northwest Territories (Kuyt 1992).
Rocky Mtn. population migrates 1,200 km from central New Mexico north in early Feb. Follows Rio Grande north through New Mexico, entering Colorado at the south end of the San Luis Valley. Stages 4–6 wk in San Luis Valley of s.-central Colorado in spring and fall before continuing flight to seasonal terminus. When spring migration continues, birds proceed north through w. Colorado, arriving at summer area in se. Idaho and w. Wyoming in Apr to early May (Drewien and Bizeau 1981). Migration route learned from Sandhill Crane parents. Fall flight from summering grounds to San Luis Valley takes 2–3 d (Drewien and Bizeau 1981). Flights may exceed 4,300 m altitude. After staging 4–6 wk in Colorado, birds complete flight to New Mexico in 1–2 d in early to mid-Nov. In Sep and Oct these birds concentrate premigration at Grays Lake NWR and other wetlands and pastures in se. Idaho before migrating south through ne. Utah, sw. Wyoming, w. Colorado, and n. New Mexico to winter in middle Rio Grande Valley, 48–180 km south of Albuquerque, NM. Migration route similar in spring and fall.
Diurnal migrant, rarely continuing after dark; makes regular stops to feed and rest using a variety of habitats for foraging and roosting away from human activity. Travels as singles, pairs, family groups, or flocks of 4–5 adults, sometimes joining with Sandhill Cranes for a portion of the migration. Flocks of up to 13 subadult Whooping Cranes have been seen feeding in traditional migration stopovers (staging areas) in Saskatchewan (B. Johns pers. comm.). Most common flight grouping is V-formation; modifications used when spiraling or gliding. Echelon formation is used for low-level flapping flights and at high altitude when assisted by a tail wind. Most migration occurs below 600 m altitude, but 1,500–1,800 m also common (Kuyt 1992).
Juveniles sometimes separate from their parents when spring migration begins at Aransas NWR; otherwise separate upon reaching Saskatchewan or at Wood Buffalo NP (Allen 1952, Stehn 1992b,c; E. Kuyt unpubl. data). Flying includes slow, low-level flapping and rapid, high-altitude flight with limited wing movement. The more energy-efficient passage results from repetitive sequences of spiraling upward in thermal updrafts followed by a long, slow, declining glide (Kuyt 1992). Birds may traverse 700–800 km nonstop in 9–10 h. During average conditions, travel 400 km in 7.5 h. Some evidence that navigation is partially by recognition of land features.
During migration, birds roost in shallow water in lakes, ponds, or riverine areas. After daybreak, fly or walk to loafing or feeding areas. After feeding, may wait to initiate migration until air warms enough to provide thermal updrafts. The day’s flight may end in midafternoon or later; birds then feed and rest before going to roost at dusk.
Control And Physiology
As spring approaches, Dancing, Unison-calling (Archibald 1975; see Sounds: vocalizations), and flying increase in frequency, indicative of premigratory restlessness (Allen 1952, Blankinship 1976). Northward migration often coincides with easterly movement of a high-pressure system which provides southerly tail winds, a rising barometer, and clear weather. Southerly movements coincide with northerly winds, good visibility, and increasing barometric pressure (Kuyt 1992). Behaviors characterizing premigration are increased alertness, preening, wing comfort movements, and head tilting (called Monocular-gazing by Ellis et al. 1991, Stehn 1992a). The departure of 1 group seems to stimulate other nearby Whooping Cranes to start migrating.