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well as adjacent shelter and nest <br />sites. However, other species that <br />Interfere with the nesting of riparian <br />birds by either being predators or <br />nest parasites have also increased <br />(e.g., European starling CSturnus <br />vulaaris], brown-headed cowbird <br />CMolothrus ater7, bronzed cowbird [M.. <br />aeneus], great-tailed grackle <br />[Quiscalus mexicanus]). <br />Changes have resulted in the <br />development of open water and marsh <br />habitats. In these situations, many <br />waterbirds have benefited. Grinnell <br />(1914:72-73) commented on the paucity <br />of waterbirds in 1910: <br />...The little open water some- <br />times attracted a few tran- <br />sient ducks and mudhens, but <br />so far as known no water bird <br />outside of the Ardeidae remain <br />to breed anywhere along the <br />Colorado River. <br />Among the many waterbirds occupying <br />these habitats today is the Federally <br />endangered Yuma clapper rail (Rallus <br />longirostris y_umanensis) (Figure 24). <br />The almost annual occurrence of <br />rare duck species and typical oceanic <br />species is associated with the forma- <br />tion of the large lakes and deep chan- <br />nels not historically found along the <br />lower Colorado River. Dispersing <br />waterbirds from the Gulf of California <br />are also attracted to these large <br />bodies of water. With a decline of <br /> <br />Figure 24. Yuma clapper rail is the <br />only bird species on the Federal en- <br />dangered species list with the center <br />of its distribution on the lower Colo- <br />rado River. Photo by,R.E. Tomlinson. <br />native riparian breeding birds there <br />has been an increase in the establish- <br />ment and expansion of primarily <br />wintering species associated with <br />agriculture, open water, and marsh <br />habitats. <br />The large diversity of bird <br />species now found along the lower <br />Colorado River is primarily a result <br />of changes undertaken to "modernize" <br />the river. A number of species not <br />found in Grinnell's day are now common <br />or increasing. However, the valley's <br />original breeding avlfauna associated <br />with pristine riparian habitats, like <br />the original ichthyofauna associated <br />with pristine aquatic habitats, is in <br />jeopardy. <br />29