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<br />Willow flycatchers may remove cowbird eggs, or more commonly, may abandon the nest if the <br />parasite's eggs are deposited. The second nesting attempt is energetically expensive because a <br />new nest may be constructed (Sogge 1994), although Brown (1988) noted a pair covered a <br />cowbird egg with fresh nesting material and laid a new clutch. The second nest, already at a <br />temporal disadvantage, often is parasitized as well. Cowbird parasitism could be largely <br />responsible for the absence of southwestern willow flycatchers in otherwise suitable habitat in the <br />Grand Canyon (Unitt 1987). Bronze cowbirds (Molothrus aenus), also brood parasites, recently <br />have also been reported moving into the Grand Canyon (Sogge 1994). <br /> <br />Effects of'the Proposed Action on Southwestern Willow Flycatchen <br /> <br />The proposed October Test flow is unlikely to exert any direct impact on the Grand Canyon <br />population or nesting sites of southwestern willow flycatchers. The four historical nesting sites in <br />Grand Canyon were the focus of impact studies related to the 1996 test flow (Stevens et al. <br />1996). This release was 45,000 cfs, and occurred in March, 1996. Nest site trees lie at or above <br />the 45;000 as stage, and the nest trees and nest site stands did not sustain direct damage from the <br />1996 test flow. The current proposed flow of 31,000 will not damage nesting habitat. <br /> <br />All recent E.I. e:aimw nests in upper Grand Canyon have been 1<nted in matuIe Tamari% <br />ramo3i33ima trees. Because tamarix bas a deep tap-root and is a long-lived species ~ 100 yr, <br />Stevens 1989a,b), it is unlikely that plants established immediately above the wetted perimeter <br />will be greatly affected by this change in operations. These southwestern willow flycatcher <br />nest site trees bad all persisted through flows in excess of 92,600 as in 1983 (U.S. Bureau of <br />Reclamation 1996). During the 1996 test flow, two nest stands lost a small amount of area <br />due to scour during the high flows (Stevens et al. 1996). Reduction in branch diversity in the <br />first lA-meter above the ground occurred at tIm:e sites, and two sites bad significant loss of <br />litter and under story vegetation; however, there was no reduction in branch height diversity of <br />diversity of mllY;mum foliage height at any site, nor was any change in vegetation composition <br />observed in the nest tree stands. Thus the 1996 test flow resulted in no biologically important <br />impacts to the Grand Canyon E.I. exthmu nest site trees or stands. The proposed October Test <br />flow will be of much lesser mlll";tnde and is therefore not expected to impact SWWF nesting <br />habitat. <br /> <br />Southwestern willow flycatchers arrive in the Grand Canyon area in mid~May, and have <br />migrated from the area by Ma1ch. No SWWF are expected to be present during the 48 hour <br />Test flow and no direct effects will take place. <br /> <br />In contrast to the nest site stands, the wetlands occurring on low terraces and associated with Rt. <br />extimus nest sites in Grand Canyon are resilient plant assemblages that develop under a discrete <br />suite of inundation frequency and sediment grain-size gradients (Stevens et al. 1995). Marshes <br />are renown as highly productive, diverse habitats. Marsh vegetation prospers under relatively high <br />daily inundation frequencies (0.1 to 0.5, species dependent). The proposed action is designed to <br />conserve sediment in the system which will contribute to bank stability, and therefore is unlikely <br /> <br />30 <br />