Ecology of Rocky Mountain greater sandhill cranes.

Authors(s): R. C. Drewien

Publication:

Publisher:

Publication Date: 0000-00-00

Type: PhD

Location: Moscow Idaho

Abstract: This study examined the status, reproduction, and distribution of the greater sandhill crane (Grus canadensis tabida) at Grays Lake during 1969-1971. May aerial counts indicated 554 and 544 cranes in 1970 and 1971, respectively. An estimated 250 pairs nested at Grays Lake; the high nesting density of 200 pairs within a 10,000 ha area is the highest density reported for cranes in North America. Most of the 337 nests located were located in wet meadow/marsh zones along the bulrush/cattail edge; 56% were in water when first located and 44% were on dry ground. Nest site locations and construction are described. Egg-laying began in late April or early May; incubation was estimated at 30 days. Mean clutch size was 1.94 eggs and included 24 one-egg and 3 three-egg nests. Nest success was 78% (n=308 nests over 3 years). Nest predation was the primarily cause of nest losses. Mean brood sizes at hatching and fledging were 1.77 and 1.35, respectively. Behaviors of incubating and brooding cranes and defense of breeding territories are described. July aerial surveys were not successful for providing information on production. Fall counts provided a description of fall staging and migration and habitat use. Peak counts in mid-September indicated 1,236 and 1,390 cranes in 1970 and 1971, respectively; fall flocks contained 16 juveniles/100 adults. Use of grain fields by cranes increased from early August to mid-September then declined with migration out of the valley. Sighting of color-marked cranes provided information on spring and fall arrival of individuals, immigration of individuals to Grays Lake in fall from areas 15-25 km away, and movements of individuals through the San Luis Valley, Colorado and to main wintering areas in western New Mexico, southeastern Arizona, and northern Mexico. The Rocky Mountain Population of greater sandhill cranes was estimated at 10,000-15,000.

Keywords: Gray's Lake, Idaho, animal, breeding, bird, Aves, ornithology, ecology, habitat, management, nest, nesting, population, mortality, predation, migration, color mark, food, forage, crane, sandhill crane, Greater sandhill crane, Grus canadensis tabida