BIOGEOGRAPHICAL SECTIONS 
Local differences in waterfowl populations 
within the Upper Chesapeake region often are 
closely correlated with local variations in the 
preponderance of various types of waterfowl 
habitat. Fifteen biogeographical sections were 
defined on the basis of kinds and proportions 
of habitats and abundance and kinds of water- 
fowl. The sections are mapped in fig- 
ure 4, 
The proportion of waterfowl wintering in 
each section (table 16) was calculated from the 
January inventory data. Three-fifths of the 
entire population was found in four contiguous 
sections along the eastern shore of Chesapeake 
Bay, (Chester River, Eastern Bay, Choptank 
River, and Blackwater-Nanticoke sections), 
About one-sixth of the population was distrib- 
uted over the large area lying south of the 
Patapsco River along the western shore of 
Chesapeake Bay and in the Patuxent and 
Potomac River sections. The remaining popu- 
lations (approximately one-fourth of the total) 
were about equally divided between the fresh- 
water areas of the north Chesapeake (Upper 
Western Shore, Susquehanna Flats, and Upper 
Eastern Shore sections) and the lower salt- 
water areas (Lower Eastern Shore and Coastal 
sections), The outstanding local concentra- 
tions were in the Chester River section, where 
more than one-fifth of the entire Upper Chesa- 
peake population was found. 
Sections that contained numerous large agri- 
cultural fields adjacent to open estuarine wa- 
ters or marsh had large numbers of Canada 
Geese, Mallards, Black Ducks, and Pintails. 
Sections that had great expanses of estuarine 
bay marsh had large numbers of many kinds 
of dabbling ducks and moderately large num- 
bers of geese, Sections containing fresh or 
brackish estuarine bays with extensive shoal- 
water areas had many diving ducks and Whistl- 
ing Swans. In sections that contained large 
areas of fresh or slightly brackish habitats, 
extensive icing sometimes drastically reduced 
waterfowl numbers in winter. Many localareas 
‘were unsuitable for waterfowl because of pol- 
lution, turbidity, and excessive human disturb- 
ance, 
Information concerning seasonal changes in 
distribution of transient and wintering water- 
fowl came from aerial census data of the 
1958-59 season (table 17). The winter of 
1958-59 was unusually severe, so the January 
counts may be atypical. The Chester River 
section and the Eastern Bay and Choptank 
River sections were important waterfowl 
areas from fall to spring. The Susquehanna 
Flats were important to waterfowl during 
the spring and fall migration periods but 
had comparatively few birds during the 
winter. 
Each of the biogeographical sections will 
be discussed separately. 
23 
UPPER POTOMAC SECTION 
Habitats 
The Upper Potomac section is primarily a 
fresh estuarine bay that is adjoined by a few 
small fresh estuarine river marshes and a 
few stretches of river bottomland. This sec- 
tion once had extensive beds of wildcelery, 
naiad, and sago pondweed and lush stands of 
wildrice, dotted smartweed and other river 
marsh species. Most of the marshes now have 
been eradicated to make way for airfields or 
building sites. The river itself is so heavily 
polluted and silted that the upper half of the 
section (between Washington, D. C., and Chic- 
amuxen Creek in Charles County, Maryland) 
is completely devoid of submerged vascular 
plants. 
Waterfowl 
The Upper Potomac section formerly was 
one of the best waterfowl areas in the Upper 
Chesapeake region, with many thousands of 
dabbling ducks and diving ducks. Now the 
greatly reduced populations are largely re- 
stricted to the areas below Chicamuxen Creek, 
where fairly large beds of submerged plants 
still occur. The effects on waterfowl of the 
gradual deterioration of the upper Potomac 
estuary are vividly described by Slavik and 
Uhler (1951), and Linduska (1959), 
January inventory data during the years 
1955-58 showed that the Upper Potomac win- 
tering population of waterfowl ranged from 
2,600 in 1957 to 10,300 in 1956, and averaged 
6,400. Proportions of the various species at 
different seasons are shown in table 18. 
Largest populations were present during late 
fall and early spring, when Black Ducks, 
Canvasbacks, and Ruddy Ducks were most 
numerous. Mallards, Black Ducks, and Can- 
vasbacks were predominant in winter. 
CENTRAL POTOMAC SECTION 
Habitats 
The Central Potomac section has extensive 
shoal waters of slightly brackish estuarine 
bay where there are great beds of submerged 
aquatic plants, The section also contains sev- 
eral fair-sized estuarine river marshes, 
Waterfowl 
This section is the best waterfowl area in 
the western portion of the Upper Chesapeake 
region. January inventory data during the 
