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Predator Control for Whooping Crane and Sandhill Crane
Production at Grays Lake National Wildlife Refuge, Idaho


Wildlife Research Institute, University of Idaho, P. 0. Box 3246, Moscow,
ID 83843; Southeast Idaho Refuge Complex, 1246 Yellowstone Avenue A-4,
Pocatello, ID 83201

Intensive predator control was conducted during 1977-89 at Grays Lake National Wildlife Refuge to support the whooping crane (Grus americana) cross-fostering experiment. Reducing coyote (Canis latrans) and red fox (Vulpes vulpes) predation on whooping crane eggs and young was the objective of the control program. (Throughout this abstract 'control' refers to the predator control program.) Grays Lake, located in southeastern Idaho, is a large (8,900 ha), high attitude (1,946 m) palustrine emergent wetland dominated by hardstem bulrush (Scirpus acutus). The 42,000-ha predator control area included the Refuge and all lands within 5 km of the Refuge boundary. Prior to 1977, no predator control occurred near the refuge since termination in 1972 of two compound 1080 stations in the surrounding area. Control methods included aerial gunning, M-44s, trapping and snaring, and opportunistic shooting. During 1977-89, 652 coyotes and 247 red foxes were taken. Helicopter hunting was the most effective method for controlling coyotes (75% of the removals), but accounted for only 20% of foxes removed. Most foxes were taken by trapping (28%) and M-44s (26%). Foxes increased from 0% of the canids removed in 1977 to 73 % in 1989. Control efforts were directed at canids, but striped skunks (Mephitis mephitis) and badgers (Taxidea taxus) were taken opportunistically. Raccoons (Procyon lotor) are exceedingly rare at Grays Lake. Avian predators accounted for a small portion of the predator losses and were not controlled. Predator control enhanced (P<0.05) hatching success of whooping crane eggs. Only 6 % of 288 whooping crane eggs translocated into sandhill crane (G. canadensis tabida) nests were lost to predation, compared with a 13 % predation rate on 341 sandhill crane nests prior to predator control.

The control program was effective in 11 of 13 years in reducing sandhill crane nest losses to predators. During those 11 years fewer sandhill crane nests (6% of 247 nests; P<0.05) were destroyed by predators. The relationship of predator control with fledgling success of whooping and sandhill cranes was less clear. Annual fledgling success of both species was correlated (r=0.548; P=0.043), suggesting that similar factors affected both species. Fledgling success appears to be primarily affected by extrinsic factors, especially weather patterns that affect availability of food and water during the brood-rearing period. Predator control probably enhanced survival of young in those years when good brood-rearing conditions prevailed, but had little effect in poor years.

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