858 U.S. NATIONAL MUSEUM BULLETIN 23 7 taet 2 



limited distribution. Not only are food chains disrupted, but 

 reproductive failures often result from slight ingestions of DDT. 

 Considering the dusky's dependence on insect and animal food and 

 its extremely limited distribution in an area sprayed heavily for 

 mosquito control over a number of years, it is miraculous that any 

 have survived. 



The mosquito control impoundments completed in 1956 have 

 already altered or ehminated much of the vegetation in which the 

 duskies formerly nested. The gradient of the salt marsh is such that 

 the fresh water in the impoundments is deepest near the tidal area 

 of the Indian River and shallows to damp marsh near the high ground. 

 Consequently the vegetation a quarter to a half mile from the river 

 has been relatively unaltered, except for the encroachment of a few 

 cattail stands. Although the higher marsh looks ideal for nesting, 

 it is some distance from the birds' usual feeding grounds in the tidal 

 area. Some duskies have moved into this higher portion of the 

 marsh, but the food supply there may not be large enough to support 

 a dense population. 



Present in the marshes are a number of natural predators. The 

 rice rat (Oryzomys palustris) is quite common and builds its ball-like 

 nests in the tall Spartina. The racoon (Procyon lotor) is abundaat 

 in the area, and its tracks and trails may be found all through the 

 marshes. Among the commoner snakes are the banded water snake 

 (Natrix sipidon), the king snake (Lampropeltis getulis), the pigmy 

 rattlesnake (Sistrurus militanus) , and the water moccasin (Agkistrodon 

 piscivorus). All of these probably consume some eggs or young, but 

 they have always been there and their depredations have not affected 

 the dusky population measurably in the past. Several duskies have 

 been noted to desert their nests when large black ants, common in 

 the marsh, built their mud nests in the same clump of Spartina. 



Possibly more serious may be predation by two new animals that 

 have moved into the marshes since they were freshened. The large 

 pig frogs (Rana grylio) which are now abimdant within the dikes 

 may not be able to catch adult sparrows, but they could certainly 

 capture nestlings. Boat-tailed grackles (Cassidix mcxicanus), well 

 known to be fond of the eggs and young of other birds, are now 

 nesting in bushes on the dikes near the dusky colonies. Should either 

 of these suspicions prove correct, the frogs could be easily eliminated 

 by flooding the impoundments temporarily with salt water, and the 

 grackles discouraged by cutting down the bushes in which they nest. 



Fall and winter. — Shortly after the molt commences in the fall 

 the duskies become very shy and elusive. They no longer respond to 

 a squeak by flying to the top of the grass to watch and scold the 

 intruder. One gets the impression that fewer birds are present in 



