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. . .' " Area Manager DRAFT 21 listed as endangered October 23, 1991 (56 FR 54957). As Bestgen (1990) pointed out: Reasons for decline of most native fishes in the Colorado River Basin have been attributed to habitat loss due to construction of mainstream dams and subsequent interruption or aIteration of natural flow and physio-chemical regimes, inundation of river reaches by reservoirs, channelization, water quality degradation, introduction of non-native fish species and resulting competitive interactions or predation, and other man-induced disturbances (Miller 1961, Joseph et al. 1977, Behnke and Benson 1983, Carlson and Muth 1989, Tyus and Karp 1989). These factors are almost certainly not mutually exclusive, therefore it is often difficult to determine exact cause and effect relationships. The razorback sucker recovery goals identified streamflow regulation, habitat modification, predation by non-native fish species, and pesticides and pollutants as the primary threats to the species (Service 2002b). Within the upper Colorado Basin, recovery efforts include the capture and removal of razorback suckers from all known locations for genetic analyses and development of discrete brood stocks if necessary. These measures have been undertaken to develop broodstock lineages such that, if these fish are genetically unique by subbasin or individual population, then separate stocks will be available for future augmentation. Augmentation (stocking) may be the only means to prevent the extirpation of razorback sucker in the upper Colorado Basin. Summary of Status and Distribution In 2003, the Service produced a memorandum assessing the "Sufficient Progress" under the Upper Colorado River Recovery Program and oflrnplementation of Action Items in the December 20, 1999, IS-Mile Reach Programmatic Biological Opinion. In that memorandum, the Service presented a summary of pikeminnow and razorback sucker in rivers other than the San Juan (Table 3). Southwestern Willow Flycatcher Species/Critical Habitat Description The flycatcher is a small grayish-green passerine bird in the Family Tyrannidae. It measures approximately 5.75 inches and has a grayish-green back and wings, whitish throat, light gray- olive breast, and pale yellowish belly. Two white wing bars are visible in adults; juveniles have buffY wing bars. The eye ring is faint or absent. The upper mandible is dark, and the lower is light yellow grading to black at the tip. The song is a sneezy "fitz-bew" or a "fit-a-bew" and the call is a repeated "whitt." The flycatcher is one of four currently recognized willow flycatcher subspecies (Phillips 1948, Unitt 1987, Browning 1993). It is a neotropical migrant that breeds in the southwestern North America and winters in southern Mexico, Central America, and northern South America (Phillips 1948, Stiles and Skutch 1989, Peterson 1990, Ridgely and Tudor 1994, Howell and Webb 1995).