Long-billed Curlew (Numenius americanus): a technical Conservation Assessment Prepared for the usda forest Service, Rocky Mountain Region, Species Conservation Project December 12, 2006 James A. Sedgwick
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- Long-billed Curlew SUR
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12 13 males per km 2 in Idaho (n = 2 years; Redmond et al. 1981), 0.59 to 2.36 pair per km 2 in Utah (2 locations, 3 years; Paton and Dalton 1994), and 2.08 to 2.13 pairs per km
2 (Ohanjanian 1987), 3.33 to 5.00 pairs per km 2
km 2 (Hooper and Pitt 1996) in British Columbia. In winter, curlews are distributed in the United States mostly in coastal and inland regions of California, Texas, and Louisiana (Figure 3). In California, long-billed curlews occur along the coast, in the intermontane valleys of the Coast Range, in the Central Valley, Antelope Valley, and Imperial Valley, and in the Salton Sea Basin (Small 1994). Along the Gulf of Mexico, long-billed curlews occur along the coast and in the coastal plain of Texas to western Louisiana. Total numbers seen per party hour on CBCs, 1966 to 2003, ranged from a low of 0.025 (2,650 individuals) to a high of 0.12 (10,312 individuals) (Figure 3; National Audubon Society 2005). In Mexico, long-billed curlews winter in suitable estuary habitat along both coasts of Baja California (Morrison et al. 1992) and along the Pacific coast from Sonora south to Colima, Mexico. Curlews winter along the Gulf Coast of Mexico south to the Yucatan Peninsula and occur locally below 2,500 m in interior Mexico (Howell and Webb 1995). Total numbers seen per party hour on CBCs in Mexico from 1989 to 2003 ranged from a low of 0.13 (32 individuals) to a high of 2.60 (2,448 individuals) (National Audubon Society 2005). The breeding distribution of long-billed curlews has decreased with the destruction of breeding habitat and over harvesting during migration, most of this occurring prior to 1900 (Dugger and Dugger 2002). Their breeding range formerly included southern Michigan, Iowa, southern Wisconsin, coastal Texas, Illinois, Arizona (Dugger and Dugger 2002), Manitoba (Thompson 1890), and Minnesota (Roberts 1919). Their former breeding range may also have included parts of the southeastern United States (i.e., the Carolinas, Georgia, and Florida; Wickersham 1902). Curlews formerly bred in much of Kansas and the Dakotas, but they are now restricted to extreme southwestern Kansas and the western Dakotas. In Colorado, they formerly nested regularly in the eastern prairies, but now they are restricted to extreme southeastern Colorado (McCallum et al. 1977). In addition, the species may formerly have been more abundant across its present range; populations today have become more isolated (Dugger and Dugger 2002). Similar declines are thought to have occurred on the species’ winter range. Curlews were once common along the Atlantic Coast south of Massachusetts. They wintered in South Carolina (Bent 1929) and were Figure 3. Relative winter season distribution and abundance (birds per 100 party hr) of long-billed curlew based on Christmas Bird Count data from 1966 to 1989. 12 13
SUR 3 2 1 0 1967 1972 1977
1982 1987
1992 1997
2002 YEAR COUNT common during winter in Florida (Stevenson and Anderson 1994). Today, sightings along the Atlantic coast are extremely unusual. Population trend Historically, the breeding range of long-billed curlews has contracted, and a long-term population decline is evident (Dugger and Dugger 2002). Significant declines occurred throughout the species’ historic range during the last half of the 1800’s (Grinnell et al. 1918, Bent 1929); loss of breeding habitat in the eastern portions of its historic range coincided with curlew population declines on migration and wintering areas along the Atlantic Coast. Population declines have continued to the present (e.g., Ryser 1985, South Dakota Ornithologists’ Union 1991, Sauer et al. 2005). These declines have been attributed to historical losses of breeding habitat and the conversion of native prairies to agriculture (Fairfield 1968, Gollop 1978, McNicholl 1988), and are likely to continue as more native rangeland is converted to cropland (Robbins et al. 1986) and urban development (Fairfield 1968). BBS data from 1966 to 2004 indicate that survey-wide (U.S. and southern Canada), long- billed curlews are declining at an annual rate of 1.6 percent per year (P = 0.08; Figure 4). Other statistically significant (P ≤ 0.05) declines by region (where n >25 BBS routes), include USFWS Region 6 (2.7 percent per year; Figure 5), the Central BBS Region (3.2 percent per year; Figure 6), and Colorado (10.3 percent per year). Marginally significant declines (0.05 <P ≤ 0.10) occurred in the Great Plains Roughlands Physiographic Stratum (2.8 percent per year; P = 0.09), South Dakota (2.8 percent per year; P = 0.07), and the United States (1.9 percent per year; P = 0.07). The BBS trend estimates map (Figure 7) suggests that the declines are occurring for the most part in USFS Region 2 states, plus much of Montana, Utah, and North Dakota. Only in the Great Basin do curlew populations appear to be stable (Dugger and Dugger 2002). If subspecific designations are valid (see Systematics and Species Description, above), Numenius americanus americanus (central U.S. populations) has suffered a relatively greater decline in breeding distribution and is currently declining at a faster rate than N. a. parvus (northern and western populations). Activity pattern In Sonora, Mexico, northward migration occurs from March through early May (Russell and Monson 1998). In Costa Rica, long-billed curlews have been recorded on their wintering grounds through mid-April (Stiles and Skutch 1989). Early-spring arrival dates include 17 February for Texas (Oberholser 1974), 7 February in Nevada (Alcorn 1988), 15 March in Figure 4. Population trend (average number of birds per route) of long-billed curlew survey-wide (U.S. and Canada) from 1966 to 2004. Yüklə 1,74 Mb. Dostları ilə paylaş:
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