1548 U.S. NATIONAL MUSEUM BULLETIN 237 part 3 



by tidal flux of the brackish bay waters. The marsh vegetation in 

 response to these conditions is arranged in three zones, corresponding 

 roughly to the amount of daily submergence each zone experiences. 

 Fringing the lower edge of the marsh adjacent to the bay is a broad 

 expanse of cordgrass (Spartina joliosa) , and on the higher reaches of 

 marsh grows pickleweed (Salicornia ambigua). Lastly, along the 

 raised banks of tidal sloughs, which carry water into and out of the 

 marsh, grows a gumplant (Grindelia cuneifolia). This gumplant, 

 which reaches the size of a small bush, affords a great deal of cover when 

 mixed with the pickleweed; here the marsh song sparrows find con- 

 ditions most suitable for their existence. 



The tides thus set the pattern assumed by the dominant plants 

 on the marsh, and in so doing strongly influence the areas in which 

 the song sparrow lives. High tides also have other effects on the 

 birds. High spring tides, which can flood nests of song sparrows, 

 occur in late April, May, and June in nocturnal hours; high winter 

 tides, which may influence the amount and direction of movements 

 of song sparrows, occur mainly in December during daylight hours. 



Nesting, territory, eggs. — In lowland California song sparrows 

 tend to begin breeding activities fairly early in the year, ordinarily 

 in late March, but the song sparrows that breed earliest are those 

 living on salt marshes (Johnston, 1954). The first date for a com- 

 pleted clutch of M. m. samuelis is February 28, and the modal date 

 for population-wide completion of clutches is March 28; corresponding 

 dates for song sparrows living in the hills around the San Francisco 

 Bay area are March 25 and April 15, respectively. The marked 

 earliness of breeding in the salt marsh birds probably is an adaptation 

 to tidal conditions, for if these song sparrows bred at the same time 

 that the upland birds do, spring flood tides would destroy many 

 eggs and young (Johnston, 1956a). Birds hereditarily endowed for 

 earliness of breeding thus leave more offspring than those breeding 

 late. [M. m. pusillula also breeds early. — V.N.] 



Salt marsh song sparrows are double-brooded; almost all pairs 

 nest twice in a season. If replacement nests are considered, each 

 pair will nest on the average 2.5 to (rarely) 3 times each season. 



The song sparrows place their nests in clumps of pickleweed, among 

 stalks of cordgrass, or in crotches of gumplant. All nests are low to 

 the ground, as the average height of marsh vegetation is less than 2 

 feet. Nests in fact average only 9% inches above the ground; they are 

 higher on the lower marsh, averaging there about 12 inches high. 

 Nests are not used more than once, and the two or more nests of any 

 one season are built at different sites within a territory. 



