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<br />response to increases in riparian vegetation following reductions in major flood discharges. This
<br />species feeds on insects and nests in tamarisk in the new high water zone (Brown 1991).
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<br />In the 1980's, the population of southwestern willow flycatchers in Arizona was believed to have
<br />been no more than a few dozen pairs, with the largest number of individuals in the Grand
<br />Canyon (Unitt 1987). However, only two pairs were located in the Grand Canyon in 1991
<br />(Brown 1991). In 1992, when comprehensive nest monitoring was initiated, two pairs were
<br />present, with only one establishing a nest. That nest successfully fledged three flycatchers
<br />(Sogge and Tibbitts 1992). In 1993, one breeding pair, one male with two females, and six
<br />unpaired males were detected. Three nests were found, all of which were parasitized by the
<br />brown-headed cowbird. None were successful in rearing flycatchers (Sogge et at. 1993). Four
<br />pairs and one unpaired male occupied the Grand Canyon in 1994. Nine nests were attempted,
<br />at least four of which were parasitized by cowbirds. All nesting attempts failed (Sogge and
<br />Tibbitts 1994). In summary, since 1992, 9 pairs of willow flycatchers have made 13 nesting
<br />attempts in the Grand Canyon, 1 of which successfully fledged 3 flycatchers.
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<br />A number of published reports and papers have documented the status, distribution. and nesting
<br />characteristics of southwestern willow flycatchers in Grand Canyon (U. S. Bureau of Reclamation
<br />1996a). Nesting habitat was summarized as occurring in wide river reaches with broad stands,
<br />of riparian vegetation, usually tamarislc about 4-7 m in height with occasional overstory and
<br />dense foliage 0-4 m from ground, and usually proximal to fluvial marshes or exposed sandbars
<br />(Brown and Trossett 1989, Tibbitts et al. 1994). Nests were usually over moist or wet soil and
<br />about 3.5 to 7 meters above ground.
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<br />Glen Canyon Dam closed in 1963, significantly changing the upstream and downstream
<br />ecosystem of Colorado River. Upstream, Glen Canyon and other reaches of the river that
<br />supported riparian vegetation for over 300 Ian were inundated by Lake Powell. Because of
<br />reservoir fluctuations and substrate types, the perimeter of Lake Powell only supports limited
<br />riparian vegetation, primarily at tributary confluences.
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<br />Downstream, woody riparian habitat existed above the zone that was regularly scoured by flows
<br />of 2800 cms. The mesquite (Prosopis glanduIosa), catclaw (Acacia greggil), and hackberry
<br />(Celtis reticulata) riparian that existed above those floods continued after the dam but are
<br />perched above the river and only infrequently flooded (U.S. Bureau of Reclamation 1995bl.
<br />This area" termed the "upper riparian zone" or "old high water zone," was approximated hy
<br />Stevens (written communication in 1995 FEIS) to be 750 hectares.
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<br />The riparian vegetation that developed in the zone below the old scour line and the high water
<br />from the powerplant at Glen Canyon Dam has been termed the "lower riparian zone" or the
<br />"new high water zone." Stevens estimated that vegetation occupies about 530 hectares of {hat
<br />zone. Common woody species include tamarisk, seep-willow (Baccharis salicifolia). ~oy"te
<br />willow (SaIix exigua), and limited stands of Goodding willow (SaIix gooddingil) (U.S. Bureau
<br />of Reclamation 1995b).
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<br />Biological and Conference Opinions Glen Canyon BeachlHabital-Building Flows 2116/96
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