The Fluvial Hydrologic and Geomorphic Context for the Recovery of the Endangered Southwestern Willow Flycatcher

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The southwestern willow flycatcher (Empidonax traillii extimus) is a riparian bird that spends winter months in Central and South America and summer breeding months in riparian zones of the American Southwest. Decline of the willow flycatcher population to less than 1000 breeding pairs prompted the Federal government to declare the species endangered, triggering a major recovery effort. The most important aspect of recovery is management and improvement of the riparian habitat of the bird population. Although the direct management of the species is primarily a biological issue, fluvial hydrology and geomorphology play an important role in understanding the dynamics of the present bird population and in designing a recovery plan because these physical systems are the substrates for the living communities which include the birds. Contributions of geomorphology and hydrology to the recovery plan include the use of watersheds and river basins as planning and evaluation units; understanding the connections between fluvial forms and riparian vegetation; implications for the bird population of the magnitude, frequency, duration, timing, and rate of change for various river discharges. The installation and operation of dams are the most important causes of hydro-geomorphic and ecological change in the region, so that management of these structures offers primary opportunities to improve the physical and biological conditions for the endangered species.

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