in south San Francisco Bay. By census from a 

 boat in flooded marsh, he found 0.57 rails per ha 

 in a 14 ha section of marsh. Zucca (1954), also 

 using the boat count method in flooded marsh, 

 found 0.49 rails per ha. Based on these data Gill 

 (1972) estimated that the number of rails in south 

 San Francisco Bay ranges from 2,420 to 2,880 

 (average 2,750). Probably 50% or more of all 

 California clapper rails are in that area, where, 

 until recently, they appeared to be maintaining 

 their numbers. However, loss of their already 

 restricted habitat continues and total numbers are 

 probably being reduced. Some evidence indicates 

 that nesting success may also be declining (R. Gill 

 pers. comm. to Wilbur and TomHnson 1976). 



REPRODUCTION 



Nesting season begins in mid-March and ex- 

 tends into July (DeGroot 1927). Data for 128 

 museum egg sets indicate even distribution of 

 nesting from 1 April through 10 May, with only 

 six later records, but concentration of collecting 

 activity during periods when eggs are most likely 

 to be found may bias data (Wilbur and Tomlinson 

 1976). DeGroot (1927) recorded a peak in nest- 

 ing activity between 10 and 25 April, almost com- 

 plete cessation of nesting from 15 May to 15 June, 

 then renewed activity during late June and early 

 July. Applegarth (1938) and Gill (1972) recorded 

 a similar pattern but peak of activity was in May 

 rather than April. DeGroot (1927) estimated that 

 perhaps 50% of the birds raise two broods per 

 year. Zucca (1954) and Gill (1972) suggested 

 that late nestings were undertaken when first 

 clutches were destroyed by high tides in May and 

 June. Wilbur and Tomlinson (1976) suggest that 

 late nesting by California clapper rails may in- 

 clude both renesting attempts and second broods. 



Apparently complete clutches are reported to 

 contain from 5 to 14 eggs, most commonly 6 to 

 10 eggs (Bryant 1880, Cohen 1895, DeGroot 

 1927, Applegarth 1938, Zucca 1954, Gill 1972). 



Both sexes incubate the eggs, which hatch in 

 23 to 29 days (Applegarth 1938; Zucca 1954; 

 Johnston 1956). Hatching requires approximately 

 48 hours after pipping Qohnston 1956). Incuba- 

 tion probably begins with laying of the last egg 

 and ceases when first egg hatches (Zucca 1954). 



There is no specific information on nesting 

 success (Wilbur and Tomlinson 1976). Norway 

 rats {Rattus norvegicus) are known to have 



destroyed rail eggs but authorities disagree as to 

 the magnitude of this loss (Cohen 1895, Bryant 

 1880, DeGroot 1927, Zucca 1954). Other nest 

 losses are attributed to unknown mammals 

 (Bryant 1915) and nest inundation by high tides 

 (Zucca 1954). 



MANAGEMENT 



The California Department of Fish and Game 

 considered reintroduction of clapper rails at 

 Monro Bay in 1972, using stock from San Fran- 

 cisco Bay, but decided against it because of un- 

 certainty of the racial identity of the original 

 population and also the lack of information on 

 whether any of that population still existed there 

 (Sanford Wilbur pers. comm.). 



Establishment of south San Francisco Bay 

 National Wildlife Refuge and acquisition of Tubbs 

 Island and Elkhorn Slough by the Nature Conserv- 

 ancy are beginnings toward habitat preservation. 

 Proposed management includes acquisition and/or 

 agreements with property owners to retain suit- 

 able marsh habitat for this and other water-assoc- 

 iated birds and further improvement in control- 

 ling water quality in problem areas (Fish and 

 Wildlife Service 1973). 



AUTHORITIES 



Sanford R. Wilbur 

 Fish and Wildlife Service 

 1190 East Ojai Ave. 

 Ojai, CaHfornia 93023 



Robert D. Ohmart 

 Randall W. Smith 

 Dept. of Zoology 

 Arizona State University 

 Tempe, Arizona 85281 



Robert Gill 



Gordon Gould 



Howard Leach 



California Depart, of Fish and Game 



1416 Ninth Street 



Sacramento, California 95814 



PREPARER'S COMMENTS 



Although the total population of this sub- 

 species of clapper rail is still fairly substantial 

 (about 2,800 individuals), its very strict require- 

 ments for relatively unpolluted tidal salt marsh 



