SONG SPARROW: SAN FRANCISCO BAY 1549 



On one occasion (out of about 130 possible occasions) a song sparrow 

 gave a "rodent run" distraction display as it left the nest when the 

 observer visited it. 



[The measurements of 40 eggs of samuelis average 21.5 by 15.9 

 millimeters; the eggs showing the four extremes measure 24-4 by 16.3, 

 22.9 by 17.3, 19.1 by 15.8 and 20.1 by 15.0 millimeters.— W.G.F.H.] 



Mean clutch-size for salt marsh song sparrows is 3.20±0.05 eggs, on 

 the basis of 157 records collected between 1950 and 1955 (Johnston, 

 1956a). The range in mean clutch-size is from 2.91 to 3.42 eggs. In 

 any one season the earliest clutches are relatively small (to 2.83 eggs), 

 clutches completed in mid-season are relatively high (to 3.66 eggs), and 

 those of the late season low (to 2.60 eggs). Pairs of samuelis averaged 

 from 7.5 eggs to 9.1 eggs per season from 1950 to 1955. Owing to 

 unpredictable mortality to eggs and young, these figures are not a 

 reliable guide to productivity, which is best defined as the number of 

 fledglings per pair of adults per season. On the salt marsh this 

 productivity is from three to five fledglings per pair per year. 



[M. m. jpusillula also has a low mean clutch size, 3.3 eggs. — V.N.] 



Territorial relationships of salt marsh song sparrows are similar to 

 those of the species in general. In late winter and spring, male singing 

 and chasing increase. By late February and March most males have 

 established themselves on territories; pair-formation ordinarily has 

 already taken place, but those birds not yet mated now form pairs. 

 Singing decreases in late March and April, but territorial strife con- 

 tinues sporadically throughout the remainder of the breeding season. 

 Territorial activity ceases in July, but becomes evident again in late 

 August and September. Although in many instances true territories 

 are not staked out the quarters most birds, adults and juveniles alike, 

 occupy in September are identical with those of the following breeding 

 season. 



The territories of salt marsh song sparrows are small, and the 

 borders of some sloughs may support as many as 8 to 10 pairs of birds 

 per acre; most territories are thus about 30 feet wide by 150 feet long, a 

 little over 0.1 acre. Territories are larger where vegetation is sparser 

 at the heads and mouths of the sloughs than along the middle reaches. 



Adults show a strong tendency to remain permanently in the 

 territories they take up their first autumn. Very few birds move more 

 than 10 meters from this first autumn territory, no matter how long 

 they live. The longest movement recorded on banded birds (Johns- 

 ton, 1956a) is 35 meters. 



The incubation period is about 12 (12 to 14) days. Young remain 

 in the nest 9 to 12 days, but will leave prematurely at 8 days if dis- 

 turbed. Fledglings remain under parental care for 5 to 8 more days; 

 this gives a total parental period of attention per brood of about 30 



