1550 U.S. NATIONAL MUSEUM BULLETIN 23 7 part 3 



days. The adults start second broods in short order, and the first 

 young then gradually move out into other parts of the marsh. 



Dispersal by the young occurs from time of fledging until autumn, 

 when the adults again begin to show territoriality. The median 

 distance of dispersal in these young is 185 meters. The longest 

 distance on record is 960 meters (Johnston, 1956a). 



Enemies.- — -Adults are preyed upon by marsh hawks, short-eared 

 owls, and probably Norway rats. Much predation must occur for 

 which there is little record, for although adult mortality is about 42 

 percent per year (Johnston, 1956) very few birds are known to have 

 died through a specific agency. Only four skulls of song sparrows 

 appeared in 491 pellets of short-eared owls collected in a 4-year period 

 (Johnston, 1956b). 



Eggs and nestlings are subject to higher mortality than full-grown 

 birds, and for these the mortality factors are easier to determine. In 

 a sample of 504 eggs and young, about 20 percent of eggs and young 

 were killed by some predatory agent (probably Norway rats), 11 

 percent by flood tides, 5 percent by desertion of adults, 5 percent by 

 rainstorms, and about 4 percent by accidental loss of eggs from the 

 nest and parasitism by cowbirds (Molothrus ater). Total mortality 

 was 50 percent of all eggs laid. 



Plumages. — The sequence of plumages in salt marsh song sparrows 

 has not been studied, but probably is the same as for other subspecies 

 of the species. The annual molt begins in early July, almost imme- 

 diately following cessation of breeding, at which time adults are in 

 extremely poor feather owing to heavy abrasion on rough marsh plants. 

 The annual molt is completed in late August or early September, and 

 at this time most juveniles have completed the post-ju venal molt. 



[Grinnell (1909) described maxillaris as resembling the race "gouldii 

 closely in coloration and M.m. heermanni in general size; differs from 

 M.m. samuelis * * * in having the browns more extended and of a 

 deeper tone (bay rather than hazel) and in much greater size and, 

 especially, bulkier bill; differs from M.m. gouldii * * * in much 

 greater size throughout; and from M.m. heermanni * * * in that the 

 base of the maxilla is more swollen, the black streakings everywhere 

 broader, and the general tone of coloration darker." Ridgway (1901) 

 states that samuelis is "exactly like" the race heermanni in coloration, 

 but is "much smaller, with the bill more slender." He describes 

 pusillula as being "Most like samuelis but still smaller, the wings and 

 tail decidedly so ; coloration much less rusty, the general color of upper 

 parts olive-grayish, the black dorsal streaks not distinctly, if at all, 

 margined with rusty brown, the lateral crown-stripes and wings less 

 distinctly rufescent, under parts more heavily streaked (streaks usually 

 wholly black) and flanks paler fulvous; under parts usually more or 



