Sandhill Crane Nesting Habitat, Egg Predators, and Predator History on Malheur National Wildlife Refuge, Oregon

Abstract

Coyotes (Canis latrans), raccoons (Procyon lotor), and common ravens (Corrus corax) are important predators on greater sandhill crane (Grus canadensis tabida) eggs at Malheur National Wildlife Refuge, Oregon. Coyotes and ravens occurred historically at Malheur, whereas raccoons were first recorded in 1950. Of 1096 greater sandhill crane clutches (1966 to 1989), coyotes destroyed 214 (20%), raccoons 100 (9%), and ravens 162 (15%). Most cranes at Malheur select coarse, emergent vegetation for nest placement. Nesting success was highest in hardstem bulrush (Scirpus acutus) and lowest in broad-fruited burreed (Sparganium euryvarpum). In bulrush and common cattail (Typha latifolia), there were significantly more well-concealed nests, and success rates were significantly higher than in burreed and meadow. There was no difference in predation rates among concealment categories for raccoons, but ravens took significantly more poorly-concealed nests, while coyotes destroyed more poorlyand fairly-concealed nests than those well concealed. Past predation pressure has likely contributed to the greater use of concealing, coarse, emergent vegetation for nest sites. Greater sandhill cranes (Grus canadensis tabida) commonly breed in remote, isolated wetlands of northeastern California, and southcentral and southeastern Oregon. In southeastern Oregon, nesting primarily occurs in closed drainage systems, with water originating from adjoining mountain ranges. One of the largest of these wetland complexes is the MalheurHarney Lakes Basin, in Harney County, Oregon. About 100,000 ha of wetland habitat, from alkali sumps to perennial marshes and lakes, are found within the basin. A large percentage of these wetlands is located on Malheur National Wildlife Refuge (NWR), in the southern half of the system. A mean of 215 (range = 168 to 236) pairs of cranes have breeding territories on the refuge. Over 90% of these pairs nest among coarse, emergent vegetation, predominantly hardstem bulrush (Scirpus acutus), common cattail (Typha latifolia), and broad-fruited burreed (Sparganium euryvarpum). Large wetland complexes naturally attract predators, and predation rates on both crane eggs and chicks are often high (Littlefield 1976, 1995a). Common ravens (Corrus corax), raccoons (Procyon lotor), and coyotes (Canis latrans) 1 Present address: HCR 4 Box 212, Muleshoe, TX 79347. have been responsible for most losses, with all 3 species taking eggs; coyotes have been identified as the principal predator of chicks (Littlefield and Lindstedt 1992). Such predation pressure is believed to be primarily responsible for the extensive use of concealing vegetation for crane nest placement, which is inconsistent with other western United States nesting areas (e.g., Drewien 1973, Stern et al. 1987, Littlefield 1995b). Historically, predator densities have fluctuated, at least since the establishment of Malheur NWR in 1908. Disease outbreaks, poisoning campaigns, trapping, shooting, and prey availability have contributed to these fluctuations. Accompanying these predator fluctuations, habitat conditions at Malheur have also varied, particularly since the mid-1930's. Grazing cattle numbers peaked in 1973 at 126,593 Animal Unit Months (AUMs) after a steady increase beginning about 1940 (Littlefield and Thompson 1987). Even though grazing was confined to winter, little residual vegetation remained by spring, regularly leaving crane nests completely exposed in April and May. For 1966 and 1967, nest success was 44% (Littlefield and Ryder 1968), even with intensive predator control. After 1972, predator control programs were mostly eliminated, but as AUMs of graz-