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<br />. <br /> <br />. <br /> <br />Area Manager <br />DRAFT <br /> <br />31 <br /> <br />tamarisk. Tamarisk and arrowweed (Tessaria sericea) recover more rapidly from fire <br />than do cottonwood and willow. <br /> <br />. Agricultural Development. The availability of relatively flat land, rich soils, high water <br />tables, and irrigation water in Southwestern river valleys has spawned wide-scale <br />agricultural development. These areas formerly contained extensive riparian habitats. <br />Agricultural development entails not only direct clearing of riparian vegetation, but also <br />re-engineering floodplains (e.g., draining, protecting with levees), diverting water for <br />irrigation, groundwater pumping, and applications of herbicides and pesticides, which can <br />also affect the flycatcher and its habitat. <br /> <br />. Urbanization. Urban development results in many impacts to riparian ecosystems and <br />flycatcher habitat, including a variety of interrelated direct and indirect effects that can <br />cause loss and/or the inability to recover habitat. Urban development creates increased <br />demands for water use, which can deplete streams and aquifers and promote construction <br />of reservoirs and structures to control floods. Urbanization also provides the need for <br />increased transportation systems that include bridges, roads, and vehicles detrimental to <br />riparian habitat and riparian inhabitants. <br /> <br />. Brood Parasitism. Brood parasitism by cowbirds negatively affects the flycatcher by <br />reducing reproductive performance. Parasitism typically results in reductions in number <br />of flycatcher young fledged per female per year. Cowbirds have probably occurred <br />naturally in much of the flycatcher's range, for thousands of years (Lowther 1993). <br />However, they likely increased in abundance with European settlement, and established <br />in southern California only since 1900 (Rothstein 1994). At normal levels, parasitism is <br />rarely an impact on host species at the population level. However, for a rare host, <br />parasitism may be a significant impact on production of young at the population level, <br />especially with the high predation rates flycatchers and other small passerines experience. <br />When combined with negative influences of predation, habitat loss, and overall rarity, <br />parasitism can be a significant contributor to population decline. <br /> <br />. Exotic Species. Several exotic plant species have become established in flycatcher <br />riparian habitats, with varying effects on the subspecies. Saltcedar is widespread and <br />often dominant in southwestern riparian ecosystems, often forming dense mono typic <br />stands. Flycatchers do nest in some riparian habitats containing and even dominated by <br />saltcedar (McKernan and Braden 1999, Paradzick et al. 2000), and available data suggest <br />that flycatcher productivity and survivorship are similar between native and saltcedar <br />habitats. However, native riparian plant communities may be of greater recovery value <br />than saltcedar, because saltcedar in some settings facilitates a periodic fire regime, can be <br />detrimental to native riparian plants in other ways (Busch and Smith 1993), and may in <br />some cases be of lesser value to bird communities overall (Rosenberg et al. 1991). <br />However, this does not diminish the value of maintaining currently suitable and occupied <br />saltcedar habitat. Saltcedar can mimic many of the ecological functions of native riparian <br />plant species (Stromberg 1998), and in many cases supports a riparian obligate bird <br />community that would not occur in areas where habitat conditions can no longer support <br />