RITUAL REQUIREMENTS 



During the breeding season males sing from 

 prominent perches atop the glasswort, grasses, or 

 rushes. A male occasionally will flutter slowly 

 upward 7 to 12 m and then descend to its perch 

 while singing. Males chase females in low erratic 

 flights over the tops of vegetation (Nicholson 

 1928,Trost 1968). 



OTHER CRITICAL ENVIRONMENTAL * 

 REQUIREMENTS 



Nesting is confined to a male's territory, 

 which is defended by song and occasional chasing. 

 Occupied nests were found within 12 m of one 

 another in the 1930's, but territories appear to 

 have increased to 100 m in diameter in recent 

 years, due to thinning of marsh vegetation and re- 

 duction in bird densities. Banding has shown that 

 males defend the same territory year after year. 

 Banded juveniles have returned a year later and 

 established territories 300 m from where they 

 were fledged. Birds may fly 200 m or more from 

 nest sites to feeding areas (Trost 1968). 



Predation appears to occur mainly on eggs 

 and young mostly by rats (Oryzomys palustris, 

 Sigmodon hispidus), raccoons [Procyon lotor), and 

 many snakes (Lampropeltis getulus, Agkistrodon 

 piscivorous). Fish crows (Corvus ossifragus) and 

 boat-tailed grackles [Casstdix mexicanus) may rob 

 nests. Ants may force adults to abandon nests, 

 especially during high water (Nicholson 1928; 

 Trost 1968). Nesting red-winged blackbirds 

 [Agelaius phoeniceus) constantly harass duskies 

 which nest nearby (DSSRT draft). 



The dusky occupies a median position on the 

 marsh moisture gradient between the 3 and 5 m 

 contour lines. Above this elevation, the drier 

 marsh has woody growth and is vulnerable to 

 wildfire, and the eastern meadowlark [Sturnella 

 magna) replaces the dusky. In lower areas with 

 standing water and/or dense cordgrass, least 

 bitterns (Ixobrychus exilis), king rails (Rallus 

 elegans) and probably black rails [Laterallus 

 jamaicensis) occur. The dusky prefers patches of 

 cordgrass with heights of 0.5 to 1.5 m and a 

 density of approximately 1,700 stems/m^ (Sharp 

 1968, 1970). 



Natural fires seem to play a beneficial role in 

 maintaining dusky habitat along the St. Johns 

 River. Most lightning fires occur in the rainy 

 season when the marsh is wet and humidity high; 

 they move slowly and burn small, discontinuous 

 areas, removing woody plants and allowing the 



tall and short cordgrass savannah required by the 

 duskies to regenerate (Sharp 1968, Baker in 

 press). Birds in the immediate vicinity are dis- 

 placed, but presumably recolonize afterward. 



POPULATION NUMBERS AND TRENDS 



Dusky sparrow populations were probably 

 stable until the 1940's, when Nicholson estimated 

 that aerial insecticide spraying from 1942 to 1953 

 reduced numbers 70% by 1957 (Trost 1968). De- 

 creases may have resulted from reproductive 

 failure and disruption of the food chain. Sharp 

 (1968) estimated that there were 2,000 pairs on 

 Merritt Island prior to spraying, based on his ob- 

 served densities and the reports of Baynard 

 (1914) and Nicholson (1928). Impoundment of 

 the island marshes in the mid-1950's and resulting 

 changes in salt marsh vegetation reduced popula- 

 tions to four localities having 70 pairs in Trost's 

 1961-1962 study (Sharp 1968). Sharp (1970) 

 found 33 or 34 males in his 1968 survey. Baker 

 (in press) located two males at the north end of 

 Merritt Island in 1977 and none in the 1978 sur- 

 vey. 



Sharp (1970) found 372 singing males in the 

 St. Johns River marshes in the spring of 1968 and 

 estimated the probable total of the mainland 

 population to be 894 pairs. The St. Johns Nation- 

 al WUdlife Refuge surveys for 1970 and 1972- 

 1978 documented 143, 110, 54, 37, 47, 11, 12, 

 and 9 singing males, respectively. Winter wildfires 

 apparently caused the most drastic reductions. 

 Singing males in the entire St. Johns Basin num- 

 bered 28 in 1977 and 24 in 1978; no females 

 were seen in 1978, although some were seen in 

 1977 (Baker, in press). 



REPRODUCTION 



Dusky sparrows breed from March to August, 

 with two egg-laying peaks— one from late April to 

 early May and the other from late June to early 

 July, indicating production of two broods during 

 an average season. Pair formation and copulation 

 have not been observed (Trost 1968). One to five 

 eggs have been found in nests; four is the most 

 frequent clutch size (Baynard 1914, Nicholson 

 1928). The female incubates the eggs for 12 to 13 

 days and broods the young for 9 days more. Ju- 

 veniles stay in the territory about 20 days more, 

 after which the male may drive them away. Both 

 parents feed the young (Trost 1968). 



