DUSKY SEASIDE SPARROW 853 



not that plentiful today, nor do they nest nearly so close together. 

 Both the thinning of the marsh vegetation and the decrease in popula- 

 tion pressure have probahly tended to increase territory size. 



The male advertises his territory by singing from the tops of the 

 bunch grass or black rush. One male I watched moved about his 

 territory 31 times in an hour and sang an average of 25 seconds at 

 each stop. Intervals between moves ranged from 5 seconds to 4.75 

 minutes. The advertising is so effective that physical contact is 

 seldom observed between a territorial male and an invader. Once 

 when banded male 733 was feeding on his dike and an unhanded bird 

 flew onto it, he ran at the intruder with wings outspread, feathers 

 rufHed, head back, and bill slightly open. The intruder fled before 

 he was touched, and 733 did not pursue him. 



Banding has shown the males return to the same territories year 

 after year. Two males, 703 and 705, that I banded on their terri- 

 tories in 1961, 1 recaptured defending the same territories the summer 

 of 1963. I have had no returns of adult females in successive years, 

 but fewer were banded originally, and they are harder to observe and 

 to catch than the singing males. Two other males, 711 and 713, and 

 one female, 712, 1 banded as juveniles the summer of 1962, returned the 

 following year and established territories only some 300 yards from 

 where they were fledged. I have never seen a banded dusky away 

 from the vicinity where I banded it. 



The main breeding marsh on the Indian River now contains at 

 least four loose colonies of dusldes, each isolated one or two miles from 

 the other by stretches of unsuitable habitat. If no interchange of 

 birds occurs between colonies as the banding data suggest, inbreeding 

 must be the rifle rather than the exception. And if inbreeding is as 

 prevalent in other seaside sparrows as it seems to be in the dusky, it 

 is easy to see how so many weU-marked forms have developed within 

 the complex. 



Courtship. — Pair formation has never been observed in the dusky, 

 but presumably it occurs shortly after the males start to sing in 

 March. Nicholson (MS.) notes: "In late March the males begin 

 courting the females with their aerial flight songs. Also we see 

 them vigorously pursuing the females low and rapidly just above 

 the tall grass untfl both drop from sight into it. In aU the years I 

 have watched these birds I have never seen them copulate. This 

 probably occurs on the ground hidden in the thick grass after the chase, 

 for the birds usually are not seen for several minutes afterward. 

 Flight chases may be observed throughout the nesting season from 

 Aprfl into August, but one sees very few flight songs after mid-June. 

 Perhaps such arduous courting is not needed for the late renestings." 



