432 ILLINoIs NATURAL History SURVEY BULLETIN 
easily accessible than those of emergent 
aquatic species, which, in turn, are more 
easily accessible than floating or sub- 
merged aquatic plants. 
That palatability plays an important 
role in determining the food value of 
several species is also quite evident. 
Both the pickerelweed and buttonbush 
are heavy seed producers, the food is 
fairly accessible, and yet the index value 
is low. American lotus is a medium food 
producer, the seeds are fairly accessible, 
and yet the index value is very low. 
Palatability in these species must be the 
operative factor in determining their 
meager use by ducks. 
Summary 
Employing data based upon the oc- 
currence of the plants, as well as upon 
consumption by ducks of the plant 
parts, the writers have attempted to 
present an accurate appraisal of the 
value of certain plants of the Illinois 
River valley as waterfowl food sources. 
By dividing the per cent of use made 
by ducks by the per cent of abundance 
of the important aquatic and moist-soil 
plants occurring in the valley, it was 
possible to secure an index figure of 
value for each of these species. We be- 
lieve the figures obtained to be far more 
reliable indicators of value as waterfowl 
food sources than are data derived only 
from plant parts taken by the birds. 
Numerous factors, such as seed pro- 
duction and_ accessibility, influence 
sources of supply that vary with the 
habitat and year. Taking cognizance 
of these variables (as discussed under 
each species) makes it seem advisable 
to judge the value of each species on the 
figures for no one year, but to use the 
index value for the year or years that 
seem most typical. This procedure 
places 25 plants or groups in the follow- 
ing descending order of value as food 
for ducks in the Illinois River valley, 
1938, 1939 and 1940. Tables 3, 4, 5 
and 6 give comparative values for spe- 
cies and years. 
EXCELLENT Duck Foop SourceEs 
1. Rice cut-grass, Leersia oryzoides 
(Linnaeus) Swartz 
ps, 
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6. 
ie 
8. 
10. 
iH 
126 
ihe 
14. 
ie 
16. 
1b. 
Vol. 22, Art. 5 
Walter’s millet, Echinochloa Wal- 
tert (Pursh) Nash 
Wild and Japanese millets, Echi- 
nochloa crusgalli (Linnaeus) Beau- 
vois and &E. frumentacea (Rox- 
burgh) Link, respectively 
. Moist-soil smartweeds 
a. Largeseed smartweed, Po/ygo- 
num pennsylvanicum Linnaeus 
b. Nodding smartweed, Po/ygo- 
num lapathifolium Linnaeus 
c. Swamp smartweed, Polygonum 
hydropiperoides Michaux 
d. Miscellaneous, Polygonum spp. 
. Nutgrasses 
a. Chufa, Cyperus esculentus Lin- 
naeus 
b. Red-rooted cyperus, Cyperus 
erythrorhizos Muhlenberg 
c. Straw-colored cyperus, Cyperus 
strigosus Linnaeus 
Goop Duck Foop SourcEs 
Giant bur-reed, Sparganium eury- 
carpum Engelmann 
Coontail, Ceratophyllum demersum 
Linnaeus 
Teal grass, Eragrostis hypnoides 
(Lamarck) Britton, Sterns & 
Poggenberg 
. Duck potato, Sagittaria latifolia 
Willdenow 
Marsh smartweed, Polygonum 
Muhlenbergit (Meisner) Watson 
Longleaf pondweed, Potamogeton 
americanus Chamisso & Schlech- 
tendal 
Fair Duck Foop Sources 
Buttonbush, Cephalanthus occi- 
dentalis Linnaeus 
Spike rushes, principally E/eo- 
charts palustris (Linnaeus) Roemer 
& Schultes 
Water hemp, Acnida tuberculata 
Moquin-Tandon 
Marsh cord grass, Spartina Mich- 
auxiana Hitchcock 
Sago pondweed, Potamogeton pec- 
tinatus Linnaeus 
White waterlily, Castalia tube- 
rosa (Paine) Greene 
