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. . Area Manager DRAFT 32 native riparian vegetation. This is significant, because where saltcedar is strongly dominant, replacement with native species may be difficult or impossible without changes in current hydroiogic regimes. Uniike some naiive iree species, saltccdar also maintains the fine branching structure as it grows to maturity,which may make it attractive to nesting flycatehers for a longer period of time. Furthermore, saltcedar flowers throughout much of the summer, which may be important in attracting pollinating insects (a major component of flycatcher diet) throughout the flycatcher's breeding season. Throughout the western United States, large tracts of saltcedar are being cleared for purposes including water salvage, flood water conveyance, and/or wetland restoration. Such actions pose a threat to flycatchers when conducted in areas of suitable habitat (occupied or unoccupied) and when conducted in the absence of restoration plans to ensure replacement by vegetation of equal or higher functional value. Russian olive is also well-established in southwestern riparian systems, and is present in some current flycatcher nest sites. The foliage of Russian olive is more broad-leaved than saltcedar, and so may be similar to willows in the ways it affects microsite conditions of temperature and humidity. . Demographic and Genetic Effects. The total number of flycatchers is small, with an estimated I 100 to 1200 territories rangewide. These territories are distributed in a large number of very small breeding groups, and only a small number of relatively large breeding groups. These isolated breeding groups are vulnerable to local extirpation from floods, fire, severe weather, disease, and shifts in birth/death rates and sex ratios. The flycatcher may also be threatened by low effective population size, which is an index of the actual numbers of individuals breeding in a population and the number of offspring they produce. A species' effective population size may be much smaller than the absolute population size because of uneven sex ratios, uneven breeding success among females, polygyny, and low population numbers which exacerbate these factors (Marshall and Stoleson 2000). . Migration and Winter Range Stresses. Migration is a period of high energy demands, and migrating individuals must find suitable "stopover" habitat at which to replenish energy reserves needed for the next step of migration flight (Finch et al. 2000). Insufficient stopover habitat, and destruction or degradation of existing habitat, could lead to increased mortality during migration, and/or prolonged migration resulting in late arrival to wintering or breeding sites (with reduced fitness upon arrival). Recent winter surveys in portions ofCentra1 America (Koronkiewicz et al. 1998, Koronkiewicz and Whitfield 1999, Lynn and Whitfield 2000) have found that flycatcher wintering habitat is often located in lowland areas that are subject to heavy agricultural uses, many of which negatively impact key habitat components at wintering sites. The amount of native lowland forest and wet areas, habitats in which flycatchers currently overwinter, has decreased dramatically over the last 100 years (Koronkiewicz et al. 1998). Furthermore, agricultural chemicals and pesticides are still widely used in many regions through which flycatchers migrate, and in wintering sites (Koronkiewicz et al. 1998, Lynn and Whitfield 2000), thereby exposing flycatchers to potential environmental contaminants during much of the year. OUH33