Hydrologic requirements of selected native species of the Lower Colorado River

Habitat requirements for the razorback sucker, bonytail chub, and the South western Willow Flycatcher were reviewed for the study "Synthesis Report of Ecological Restoration Concepts for the LCR" (CH2M HILL, 1999) The most imp ortant factor that may affect the suitability of habitats for the razorback sucker and bonytail chub is believed to be predation of immature individua ls by non-native fish. Native fish have been unable to maintain significant viable populations in the LCR because of a reduction in protected habitat areas and because of increases in the number of species and individuals of non-native fish that have been introduced into the LCR. The Southwestern Willow Flycatcher has historically been associated with de nse cottonwood-willow vegetation communities, but recent research has indic ated that dense saltcedar stands are also utilized by the flycatcher. Water management is important in maintaining suitable flycatcher riparian habita t. Groundwater levels must be close enough to the land surface to support a dense canopy of riparian vegetation. Furthermore, Willow Flycatchers appea r to favor areas with a moist understory during their breeding season. Fina lly, periodic inundation and flooding promotes recruitment of seedlings and maintains a full tree canopy, also favored by the flycatcher. KEY TERMS: L ower Colorado River, threatened and endangered species, habitat restoration .