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I I I I I I I I I I I I I I I I I I I BIOLOGICAL OPINION Status of the Species Delta, Topock Gorge and Topock Marsh (Rosenberg et al. 1991). These centers reflect the distribution of relatively large marshes. Smaller populations occur where moderately extensive emergent vegetation is persistent, including backwaters. Elsewhere in the interior Southwest, breeding populations occur at the Salton Sea and along the Gila and Salt Rivers east to Picacho Reservoir and Phoenix in central Arizona. According to Rosenberg et al. (1991), early naturalists on the Colorado River, many of whom were familiar with clapper rails, did not record them north of the Gila-Colorado confluence and noted that "marshes were few and of small size" (Grinnell 1914). The type specimens of Yuma clapper rail were taken in 1921 on the Colorado River, in the vicinity of Laguna Dam, north of Yuma, Arizona, by Huey and Canfield (Dickey 1923). However, an earlier specimen, since lost, and presumably of this subspecies, was collected "at Yuma" in 1902 (Swarth 1914 in Rosenberg, et al. 1991). Laguna Dam was completed in 1909 and marsh vegetation became established along canals near the dam about ten years later (Rosenberg et al. 1991). Several researchers believe that this species has expanded its range to the north from brackish water marshes of the Colorado River delta after extensive damming of the LCR in the early 1900' s (Conway 1990, Rosenberg, et al. 1991). According to these researchers, the dams have created marshlands with relatively stable water conditions ideal for rails. Todd (1987) contends that extensive marshes existed historically throughout the river valley; however, the existence of many large, long-standing marshes north of the Gila-Colorado confluence before 1920 is not supported by any detailed description of the region from that period according to Ohmart et al. (1977 in Rosenberg, et al, 1991), Similarly, the California black rail, (Laterallusjamaicensis coturniculus), a related marsh species, was first reported in the marshes around Imperial Dam in 1969 and now numbers about 200 birds (Repking and Ohmart 1977). Yuma clapper rails appeared north of Laguna Dam a few years after the completion of Parker, Imperial, and Headgate Rock dams in 1938, 1939, and 1942, respectively (Rosenberg et al. 1991). The species was not collected at Topock Marsh until 1966. Today this is the most northern population center. The northernmost record is from Laughlin Bay, in 1986, on the Nevada side of the river. Rosenberg et al. (1991) cite Ohmart and Smith (1973) and Monson and Phillips (1981) as evidence that the population was localized in the Yuma area before 1940 and since has become more widespread. They point to expansions into the newly formed Salton Sea in California by the 1940' s and Picacho Reservoir in central Arizona by the 1970 I S as supporting this view. Home ranges of individuals or pairs may encompass up to 43 ha (106 ac) and may extensively overlap with home ranges of other birds. Year-round home ranges averaged 7.5 ha (18.5 ac) (Rosenberg, et al. 1991). Habitat Use 68