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Population Dynamics Population size: Current estimates for total numbers of remaining southwestern willow flycatchers are 500 or fewer nesting pairs rangewide (Unitt 1987. U.S. Fish and Wildlife Service 1995b). Approximately 100 territorial males are estimated to occur in southern California, with most nesting groups occurring in four drainages (Whitfield 1993. Griffith and Griffith 1994. Holmgren, written communication). Approximately 119 territorial males were located at 19 sites spread over 11 drainages during statewide surveys in Arizona in 1994 (Sferra et aI. 1995). Approximately 120 territorial males were located at 18 sites spread over 8 drainages in New Mexico during statewide surveys in 1994 (Parker and Hull 1994. Maynard 1995). A small number of territorial males (S 5) has been documented in both southern Utah and southwestern Colorado during 1993. 1994, and 1995 surveys. However. breeding has not been confirmed in those states (Sogge 1995a, K. McDonald, Utah Division of Natural Resources. personal communication, T. Ireland. Service. Colorado. written communication). Rangewide, 77 percent of the locations with flycatchers are comprised of five or fewer territorial males. Population stabilitv: Southwestern willow flycatcher breeding populations are extremely small and unstable. The Service believes that at current population levels. and with continuing threats, extinction of this species is foreseeable. Southwestern willow flycatchers are absent from many' areas previously occupied or are present in reduced numbers (Hubbard 1987, Unitt 1987, Sogge et aI. 1993, Sogge and Tibbitts 1994. Muiznieks et aI. 1994, Sferra et aI. 1995). Former populations in Arizona on the lower Salt River. Santa Cruz River. and lower Colorado River near Yuma have been extirpated. Small groups of one to seven willow flycatcher territories have been detected on the Santa Maria River. lower San Pedro River, Verde River, upper Tonto Creek. upper Salt River, upper Gila River. Little Colorado River, and the Colorado River in Marble Canyon (Sogge et aI. 1993, Sogge and Tibbitts 1994. Muiznieks et aI. 1994, Sferra er al. 1995). Nesting groups monitored on the Colorado River in the Grand Canyon have declined since monitoring began in 1984 (Sogge 1995c). A similar trend has been observed in the Verde Valley at.Clarlcdale where four territorial males were first observed in 1992. In 1993. two pairs were present, one nest was documented and contained a single cowbird nestling (Muiznielcs er 01. 1994). In 1994. two pairs and one unpaired male were present. Two nests were found. one of which successfully fledged two flycatchers. the other fledged a single cowbird (Sferra et aI. 1995). Data from 1995 indicate that two unpaired males occupied the Clarlcdale site (Sogge 1995a), however extensive monitoring efforts were not possible due to landowner restrictions on access to the site. In California along the Kern River, Whitfield (1993) documented a precipitous decline in the total flycatcher population (44 to 27 pairs) from 1989 to 1993. During that same period cowbird parasitism rates between 50 and 80 percent were also documented (Whitfield 1993). A cowbird trapping program initiated in 1992 has reduced cowbird parasitism rates to S 10 percent and appears to have stabilized population numbers at Kern River at 32 to 34 pairs (Whitfield 1994). Biological aod Conference Opinions Glen Caoyon BcachlHabitat-Building Flows 2116196 10