Laserfiche WebLink
<br />".~ <br />'.~','~ <br /> <br />comrl have been noted displaymg feeding beha\'inr in \'"seys 11. Peners(\n. Grand CII1\ ,'11 <br />~ational Park. personal communication). A more prevalent problem appears [0 be a [ren1a[~;de <br />parasite, tentatively identified as Leocochloridium sp. During August 1995, approximately 9 <br />percent of the adult snails expressed sporocysts indicating advanced signs of parasitism (Stevens <br />et al. 1995a). <br /> <br />Population estimates of the Kanab ambersnail at Vaseys were approximately 18,500 in March; <br />estimates for September ranged between 92,764 and 104,000 (Table 1). The wide range in <br />population numbers follow the pattern of reproduction, overwintering, senescence, and mortality. <br /> <br />The annual life cycle and overwintering reduce numbers. In March, population numbers are low <br />and the majority of individuals (94 percent) have lost their mucosal plugs and emerged from <br />winter dormancy. In March 1995, individuals ranged from 2.0 to 11.0 mm, with a mean length <br />of 7.1 nun. The individuals that successfully overwinter are large enough to reproduce by June, <br />with individuals ranging from 3.5 to 16.0 mm with a mean length of 11.2 mm. Reproduction <br />occurs primarily in July and August, with large numbers of individuals primarily dominating the <br />2 to 5 nun size class in September (Stevens et al. 1995a), <br /> <br />Southwestern WiDow Flycatcher <br /> <br />The southwestern willow flycatcher is a small passerine bird (Order Passeriformes; Family_ <br />Tyrannidae) approximately 15 centimeters long. It has a grayish-green back and wings, whitish <br />throat, light grey-olive breast, and pale yellowish belly. Two whitish or buff wingbars are <br />visible, the eye ring is faint or absent. The upper mandible is dark, the lower is light grading <br />to dark at the tip. The southwestern willow flycatcher is a riparian obligate. nesting in riparian <br />thickets associated with rivers, streams, and other wetlands where dense growth of willow (Salix <br />sp.), Baccharis sp., buttonbush (Cephalanthus sp.), boxelder (Acer negundo), tamarisk (Tamarix <br />sp.) or other plants are present, often with a scanered overstory of cottonwood (Populus sp.). <br /> <br />Surface water or saturated soils are usually present or nearby, especially early in the breeding <br />season. During drier years surface water may be present early in the breeding season with only <br />damp soil present or a total lack of soil moisture by late June or early July (Muiznieks et al. <br />1994, Sferra et al. 1995). The species composition and structure of nesting habitat varies across <br />the range from homogeneous patches of only one or several shrub or tree species that fonn a <br />single cover layer up to approximately 6 meters. to structurally heterogeneous patches of ma,ny <br />tree and shrub species with distinct overstory, sub-canopy, and groundcover levels (Brown 1988. <br />Whitfield 1990, Sedgewick and Knopf 1992, Muiznieks et al. 1994, Tibbitts et al. 1994, Sferra <br />et al. 1995, Whitfield and Strong 1995). <br /> <br />The flycatcher is a neotropical migratory species that breeds in the southwestern U.S. and <br />migrates to Mexico, Central America, and possibly northern South America during the non- <br />breeding season. The historical range of the southwestern willow flycatcher included southern <br />California, Arizona, New Mexico, western Texas, southwestern Colorado, southern' Utah. <br />extreme southern Nevada, and extreme northwestern Mexico (Sonora.and Baja) (Unin 1987). <br /> <br />Biological and Conference Opinions Glen Canyon BeachfHabital-Building Rows 2/16/96 <br /> <br />7 <br />