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seven summer-resident insectivores were considered common or abundant (Grinnell 1914; Swarth 1914), being characteristic elements of the bottom- land cottonwood-willow associations (Figure 23). All of these species have declined sharply in numbers con- comitant with the loss of large stands of mature cottonwood-willow habitat. In addition, three species of cavity- nesting birds also have declined with the decrease of tall snags or elevated dead, soft wood associated with cottonwood-willow habitats. Figure 22B. Colorado squawfish (Ptychochellus Lucius) is extirpated from the Colorado River below Glen Canyon Dam. Photo by J.N. Rinne. P11-11, ?s; Figure 22C. Razorback sucker (4rauchen texanus) still can be found at Lake Mohave and a few other locali- ties In the lower Colorado River, but natural recruitment is virtually un- known. Photo by P.C. Marsh. Changes in the avifauna generally can be divided Into three different categories: (1) species that have declined with the loss of riparian habitats, (2) species that have in- creased with the conversion of these lands to farm land, reservoirs, or marshes, and (3) species that have expanded their geographic ranges in recent years to Include the lower Colorado River Valley. Historically, 9 ri a L Figure 23. Yellow-billed cuckoo (Coccyzus americanus) with katydid in a Goodding willow. The cuckoo has de- clined in population size dramatically since the 1970's, and is now close to extirpation along the lower Colorado River mainstem. This species is representative of a dozen deep-forest, insectivorous birds nearing extirpa- tion in the lower Colorado River Val- ley. Photo by K.V. Rosenberg. Although the increase in agricul- tural lands in the valley has had a negative impact on the breeding avi- fauna, many migratory and wintering species use these areas extensively. Some species undoubtedly visit the valley more frequently as the open habitats they prefer have become more prevalent. Some riparian species may also benefit from the agricultural- riparian edge that provides food as 28