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I I I I I I I I I I I I I I I I I I I BIOLOGICAL OPINION Status of the Species of cottonwood or willow with subcanopies and a dense understory of mixed species also difficult to penetrate (Type IV Table 3). V) dense mixtures of native broadleaf trees and shrubs as in number 4 above mixed with exotics such as saltcedar or Russian olive primarily in the understory; dense ground-level tangles difficult to penetrate sometimes interspersed with small openings (Type V Table 3). The size and shape of occupied riparian habitat patches vary considerably. Southwestern willow flycatchers have been found nesting in patches as small as 0.8 hectare (ha) (e.g. Grand Canyon) and as large as several hundred hectares (e.g. Roosevelt Lake, Lake Mead). When viewed from above, the mixed vegetation types (numbers III - V, above) often appear as a mosaic of plant species and patch shapes and sizes. In contrast, narrow, linear riparian habitats one or two trees wide do not appear to contain attributes attractive to nesting flycatchers. However, flycatchers have been found using these habitats during migration. Open water, cienegas, marshy seeps, or saturated soil are typically in the vicinity of flycatcher nests. Southwestern willow flycatchers have been documented nesting in areas where nesting substrates (that is, trees or shrubs) were in standing water (Sferra et al. 1995 and 1996, R. McKernan unpubl. data), At some locations, particularly during drier years, water or saturated soil is only present early in the breeding season (Le., May and part of June). However, the total absence of water or visibly saturated soil has been documented at sites where the river channel ha s been modified (e.g., creation of artificial channels), where modification of subsurface flows has occurred (e.g., agricultural seepage), or as a result of natural changes in river channel configuration. Nest Placement and Nesting Substrate Southwestern willow flycatcher nests are typically placed in the fork of a branch with the nest cup supported by several small-diameter vertical stems. The main branch from which the fork originates may be oriented vertically, horizontally, or at another angle; stem diameter for the main supporting branch can be as small as three to four centimeters (em). Vertical stems supporting th e nest cup are typically one to two em in diameter. Occasionally, southwestern willow flycatchers place their nests at the juncture of stems from separate plants, sometimes different plant species. Those nests are also characterized by vertically-oriented stems supporting the nest cup. Spencer et al. (1996) measured the distance between flycatcher nests and shrub/tree center for 38 nests in monotypic saltcedar and mixed native broadleaf/saltcedar habitats. In monotypic saltcedar stands (n=31), nest placement varied from 0.0 meters(m) (center stem of shrub or tree) to 2.5 m. In the mixed riparian habitat (n=7), nest placement varied from 0.0 to 3.3 m. Nest height relative to the base of the nest substrate also varies across the southwestern willow 52