Laserfiche WebLink
<br />i,;~,~ <br /> <br />.'r... <br /> <br />'~.' '~J <br /> <br />Shoreline habitats in the Grand Canyon with low water velocity, such as eddies and return <br />current channels, collect ftne, nutrient rich sediments. such as clays and silts, and may develop <br />into emergent marsh habitats. Common species include cattail, bulrushes (Scirpus spp.), <br />common reed (Phragmites australis), and, near the margins, horsetail (Equisetum Iaevigatum). <br />Stevens (written communication in 1995 FEIS) estimated that a total of 25 hectares exist in the <br />Grand Canyon. <br /> <br />Eight biologists who had observed the southwestern willow flycatcher foraging in the Grand <br />Canyon reported the species primarily used the lower riparian zone (U . S. Bureau of Reclamation <br />1996a). They observed the species to "hawk" insects from perches near canopy height, over <br />marsh vegetation, backwaters, river, and open areas riparian vegetation. Gleaning of insects was <br />reported from foliage with some ground visits. <br /> <br />Diets of Empidonax flycatchers in Ontario, Canada, a 1912 study across the United States, and <br />a Wisconsin study were summarized by the U.S. Bureau of Reclamation (1996a). In Grand <br />Canyon, the southwestern willow flycatchers were observed feeding on Lepidoptera (moths and <br />a butterfly), leafhoppers (possibly Opsius stracrogalus) and hairless caterpillers (Geometridae) <br />at the ends of tamarislc branches, and throughout the day on marsh insects (U .S. Bureau of <br />Reclamation 1996a). <br /> <br />The southwestern willow flycatcher arrive in the Grand Canyon in mid-May, with males arriving <br />before females to set up territories (Tibbitts et ai. 1994, Sogge 1995c). The f11'St date nests were <br />reported by Grand Canyon researchers since active investigations began for this species in 1991 <br />was May 22 and the latest date was July 18 (U.S. Bureau of Reclamation 1996b). In Grand <br />Canyon, a clutch of 2-3 eggs are laid from late May through July (Sogge 1995c). Eggs or <br />young in nest in the Grand Canyon may be found from early June to mid-July, but may extend <br />into August (U.S. Bureau of Reclamation 1996b). <br /> <br />Much of the southwestern willow flycatcher nesting habitat in the Grand Canyon is isolated from <br />man-caused habitat disturbance or use that has favored increases in populations of brown-headed <br />cowbirds. However, the historic mule trails and correls at Phantom Ranch and the South Rim <br />are used by brown-headed cowbirds, and brood parasitism by this species has been identified as <br />a serious threat to some potential nesting sites in the Grand Canyon. <br /> <br />While the area of riparian habitat has increased since closure of Glen Canyon Dam, the canyon- <br />bound reaches present a pattern of linear habitats, often disjunct, with limited opportunity for <br />those habitats to appreciably increase. A minimum patch size for the species is difficult to <br />defme for a nesting pair, particularly when available observations are based on small sample <br />sizes because of the species' rarity. Sizes of territory patches and associated marshes were <br />measured by the U.S. Bureau of Reclamation (l996a) on four areas that have been consistently <br />occupied by territorial southwestern willow flycatchers in Grand Canyon located from several <br />!em above Nankoweap Rapid (RM 50.4) to Cardenas Marsh (RM 71). Territory size. including <br />marsh, ranged from 0.31 to 2.79 hectares. The four sites were described as wide, low gradient <br />reaches with associated fluvial marshes. <br /> <br />Biological and Conference Opinions Glen Canyon BcachlHabilal-Building Rows 2116196 <br /> <br />16 <br />