sticks with dry leaves on them, two nests were 

 made of fine stems with dry blossoms attached. 

 Nests were located on hummocks and in the 

 crotches of small shrubs just above water in dense 

 cattail and tamarisk associations (Abbott 1940). 



RITUAL REQUIREMENTS 



The rail appears to defend its territory (Tom- 

 linson in Ohmart and Smith 1973). The 'clatter 

 call' is given in unison by male and female and 

 with adjacent birds (Tomlinson in Ohmart and 

 Smith 1973). Territory size averages 1.44 ha 

 (Smith 1974). 



OTHER CRITICAL ENVIRONMENTAL 

 REQUIREMENTS 



None other than specified in other sections. 



POPULATIONS NUMBERS AND TRENDS 



A multiagency Yuma clapper rail census re- 

 corded 889 along the Colorado River in 1973 and 

 787 in 1974. In the Imperial Valley, 134 were 

 recorded in 1974 (no count in 1973). Total count 

 for the Colorado River and Imperial Valley com- 

 bined in 1974 was 921 rails (Gould 1975). Esti- 

 mated local populations in 1973 were: Topock 

 Marsh 109-136, Topock Gorge-52-65, Bill Wil- 

 liams River delta-21-35, Colorado River delta- 

 145 (Cornelius 1972, Ohmart and Smith 1973). 

 Total population was estimated at over 1,000 

 (Tomlinson in Ohmart and Smith 1973). 



Factors regulating populations include preda- 

 tion by raccoon and coyote (Abbot 1940), bob- 

 cat, feral house cat, dog, and Cooper's hawk 

 (Todd in Ohmart and Smith 1973); and habitat 

 destruction (Tomlinson and Todd 1973, Corne- 

 lius 1972). 



REPRODUCTION 



A nest with 7 slightly incubated eggs was 

 found near the Salton Sea on 12 May 1940. Obser- 

 vations along the lower Colorado River in summer 

 (8 May to 16 September) include an adult with 

 3 young 2 weeks old on 17 July (Phillips et al. 

 1964); and a nest with one egg, another with two 

 eggs, and two empty found on 5 May. A nest with 

 six fresh eggs, one with seven fresh eggs, and one 

 with seven slightly incubated eggs were found on 

 12 May. Abbot (1940) reports a clutch of six 



slightly incubated eggs on 26 May, and five 

 clutches ranging from six to seven eggs (average 

 6.5). 



The incubation period is unknown, but is 

 probably similar to other clapper rails, 21 to 23 

 days (Ohmart and Smith 1973). 



Hatching success is suggested by three quar- 

 ter- to half-grown downy chicks found on 23 

 June (Tomlinson in Ohmart and Smith 1973) and 

 three 2-week-old young (Phillips et al. 1964). 



A breeding period in May and June was indi- 

 cated by responses to taped calls (Tomlinson and 

 Todd 1973). 



MANAGEMENT AND CONSERVATION 



An annual or periodic index to abundance of 

 rails will be important in view of constant change 

 in the rivers through reclamation projects. Taped 

 call notes could be used to obtain such an index, 

 but would be costly to maintain. Since cattails 

 and tules are so important as habitat, estimates of 

 rail population size can be determined by inspec- 

 tion of aerial photographs taken periodically. Prior 

 research could determine average density of rails 

 for specific habitat types and sizes. Spot checks 

 on the ground would help to determine accuracy 

 (Tomlinson and Todd 1973). 



State, national, and international uses of 

 Colorado River water are all involved in manage- 

 ment of Yuma clapper rails. Occasionally, such 

 management, even that for fish and wildlife, if it 

 involves dredging out cattail growth, is detrimental 

 to rail survival. The main requirement in manage- 

 ment for Yuma clapper rails is that extensive 

 growths of cattails and tules must be preserved 

 throughout its range. 



AUTHORITIES 



Richard L. Todd 



Arizona Department of Game and Fish 

 2222 West Greenway Road 

 Phoenix, Arizona 85023 



Roy E. Tomlinson 



U.S. Fish and Wildlife Service 



P.O. Box 1306 



Albuquerque, New Mexico 87103 



Philip M. Smith 



1613 W.Peoria Ave. No. 2 



Phoenix, Arizona 85029 



