Invertebrates 
Invertebrates are abundant and widespread. 
Mollusks, crustaceans and aquatic insects are 
predominant. The ribbed mussel (Volsella 
demissa) is the only common pelecypod or bi- 
valve mollusk, and it is largely restricted to 
marginal areas along tidal creeks and ponds. 
A few colonies of a small clam (Cyrenoida 
flordana), are present locally. Two types of 
gastropod or univalve mollusks are abundant 
and quite generally distributed: the saltmarsh 
snail (Melampus bidentatus) andthe tiny Littoridinops 
sp. Periwinkle snails (Littorina irrorata) are fairly 
common in marginal vegetation along creeks 
that are subject to considerable tidal fluctua- 
tion. Quite a variety of crustaceans are 
characteristic inhabitants. They include os- 
tracod crustaceans (Ostracoda); copepod 
crustaceans (Copepoda); isopod crus- 
taceans (Isopoda, including Chiridotea coeca, 
Leptochelia savignyi, and Cyathura sp.); amphipod 
crustaceans (Amphipoda, chiefly Gammaridae); 
and two types of decapod crustaceans, the mud 
crabs (Xanthidae) and the blue crab (Callinectes 
sapidus). The principal aquatic insects include 
mole crickets (Gryllotalpa sp.), nymphs of drag- 
onflies (Libelluloidea), water boatmen (Corixi- 
dae), giant water bugs (Belostomatidae), larvae 
and pupae of mosquitoes (Culicidae, chiefly 
Aedes sollicitans), midge larvae (Chironomidae), 
predaceous diving beetles (Dytiscidae), water 
scavenger beetles (Hydrophilidae, including 
genera fTropisternus, Berosus, and Enochrus), 
and snout beetles (Curculionidae, chiefly 
Calendra sp.). 
Waterfowl 
The brackish estuarine bay marshes are 
especially attractive to waterfowl during the 
spring and fall migration periods. The popula- 
tions include Canada Geese and a consider- 
able variety of dabbling ducks. The more 
characteristic species are: 
Primary Species 
Black Duck 
Green-winged Teal 
Blue-winged Teal 
American Widgeon 
Secondary Species 
Canada Goose Pintail 
Mallard Shoveler 
Gadwall Hooded Merganser 
Other species of waterfowl occurring as casual 
or irregular visitors include the Whistling 
Swan, Snow Goose, Blue Goose, Redhead, Can- 
vasback, Lesser Scaup, Common Goldeneye, 
Bufflehead, Ruddy Duck, Common Merganser, 
and American Coot. 
Black Ducks and Green-winged Teal are 
quite generally distributed, but show a definite 
preference for creeks and ponds of the drain- 
16 
age systems in which marginal mud flats are 
exposed at low tide. American Widgeons and 
Gadwalls tend to concentrate on ''stillwater 
ponds'' that contain extensive beds of widgeon- 
grass or muskgrass. Hooded Mergansers are 
nearly restricted to the larger tidal creeks, 
whereas Canada Geese prefer ponds of 5acres 
or more. The other characteristic waterfowl 
species do not have well marked habitat 
preferences, although most of them seem to 
be somewhat more numerous on ''stillwater 
ponds,'' either natural or artificial. 
The "'stillwater ponds" and shallowmarshes 
often freeze over during the winter, and, 
when this happens, most of the waterfowl 
concentrate along ponds and creeks of the 
drainage systems, in areas where there is 
enough tidal current to keep the water open. 
Comparatively large numbers of waterfowl 
breed in the brackish estuarine bay marshes. 
Black Ducks are quite generally distributed, 
occurring in all of the typical plant associa- 
tions as well as in marginal upland habitats. 
Blue-winged Teal are common locally, being 
restricted almost entirely to portions of the 
marsh that contain extensive areas of marsh- 
meadow. A very few scattered pairs of Gad- 
walls usually are present. An intensive study 
of breeding waterfowl populations was made 
from May 4 to 20, 1956, inatypical 1,000-acre 
tract in southern Dorchester County. The 
population contained 67 breeding pairs of 
ducks, including 53 pairs of Black Ducks, 13 
pairs of Blue-winged Teal, and 1 pair of 
Gadwalls. Population densities were: Ducks 
of all species, 1 pair per 15 acres; Black 
Ducks, 1 pair per 19 acres; Blue-winged 
Teal, 1 pair per 77 acres; and Gadwalls, 1 
pair per 1,000 acres. Ten of the Blue-winged 
Teal pairs were located ina single 160-acre 
sector of the study tract that contained ex- 
tensive areas of marshmeadow. 
Sample counts of transient and breeding 
waterfowl were made in Dorchester County 
in the period 1954-57 (table 10). The counts 
covered approximately 39 square miles along 
tidal creeks and guts, Waterfowl on stillwater 
ponds more than 1/8 mile away from the drain- 
age systems were not counted, so American 
Widgeons and Gadwalls and certain other 
waterfowl were proportionally lower in the 
sample counts than they were in the habitat 
as a whole. In general, Black Ducks, Green- 
winged Teal, Blue-winged Teal and American 
Widgeons were the most abundant waterfowl 
during the migration periods, Waterfowl popu- 
lations were more than six times as large in 
fall and early spring as in summer. 
The gullet and gizzard food contents of 348 
waterfowl collected in the brackish estuarine 
bay marshes were examined. Widgeongrass 
(leaves, stems, rootstalks and seeds) is taken 
in large quantities by nearly all species andis 
the most important waterfowl food in this 
habitat. The seeds of Olney three-square 
represent a major food for many waterfowl 
