This enormous complex of seasonal wetlands, impoundments, agricultural lands, expansive grassland and sagebrush steppe habitat is considered by many to be the most important bird area in the state in terms of sheer numbers that utilize the habitats year round. This IBA straddles the Oregon border east of I-5, and includes three major national wildlife refuges, Tule Lake NWR and Lower Klamath NWR, on the floor of the Klamath Basin, and Clear Lake NWR, on the edge of the Modoc Plateau just to the east (which drains into the basin). During summer, when most refuges throughout the West have drawn down their water, the Klamath Basin can retain about 23,000 acres of wetlands, possibly the largest aggregation of any site in California in the breeding season (D. Mauser, pers. comm.).
Nearly 1 million waterfowl, nearly 10% of the total number of individuals along the Pacific Flyway (K. Novick, in litt.), pass through this IBA during migration. Up to 200,000 Greater White-fronted Goose of the Pacific race stage here in early spring (D. Mauser, in litt.). The number of northbound shorebirds in spring is also exceptional (e.g. 20,000 on 27 April 2001 at the Lower Sump of Tule Lake, DS) This IBA supports both of California's last remaining colonies of American White Pelican, with birds nesting on undisturbed islets on Clear Lake (2559 pr. in 1997, Shuford 1998), and at Sheepy Lake (Lower Klamath NWR), where most of northeastern California's nesting Double-crested Cormorant breed (>1000 pr., ibid). Breeding White-faced Ibis numbers have surged here, and the IBA was found to support over 1000 nesting pairs (c. of the state's population) in the late 1990s (Ivey et al. 2002). In winter, the IBA is particularly critical for Bald Eagle 60-80% of the 1000 eagles that winter in the Klamath Basin use Tule Lake and Lower Klamath NWRs, by far the largest concentration in the state. The islets of Clear Lake also support large numbers of breeding Great Basin gulls and terns, including one of three large colonies of Caspian Tern in northeastern California (Shuford 1998). Surveys in the 1990s ranked Clear Lake in the top five sites in the state for numbers of breeding California and Ring-billed gulls (Shuford and Ryan 2000). The shallow marshes on the basin refuges support large numbers of breeding waterbirds, as well as major post-breeding aggregations of species such as Black Tern (several 1000s of birds, Shuford et al. 2001).
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Despite the area's importance to birds in western North America, it remains highly threatened by agricultural practices, because of water diversions and habitat clearing (including farming on the refuges). Much of the wetland habitat of this IBA is the result of the Klamath Project, a massive water re-routing network that moves water to and from the region's major rivers (Klamath River, Lost River), reservoirs and fields. The region's agricultural operations are currently (2001) being reviewed at the federal level in light of increased restrictions on water diversions to provide adequate flows for salmon and several threatened and endangered fishes (e.g. Lost River and Shortnose suckers) in the Klamath drainage. A recent drought (2001) has affected breeding bird habitat at Clear Lake by creating land bridges to nesting islands. Recent refuge activities have addressed this problem by constructing fenced exclosures to protect nesting American White Pelicans from coyotes (DS). Increasingly, exotic plant species are invading these artificial wetlands, the most noxious being Perennial Pepperweed (Lepidium latifolium) and Purple Loosestrife (Lythrum salicaria) (K. Novick, pers. comm.).
This IBA straddles the Oregon border east of I-5, and includes three major national wildlife refuges, Tule Lake NWR and Lower Klamath NWR, on the floor of the Klamath Basin, and Clear Lake NWR, on the edge of the Modoc Plateau just to the east (which drains into the basin).
This IBA is an enormous complex of seasonal wetlands, impoundments, agricultural lands, expansive grassland and sagebrush steppe habitat.