May, 1943 
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3 
BELLROSE & ANDERSON: Duck Foop PLANTS 429 
Fig. 13.—Sago pondweed (Potamogeton pectinatus) has the reputation of being one of the 
best waterfowl food plants in North America. 
sixteenth among 25 species or groups. 
However, in the Illinois River valley it ranks 
Its low rating in Illinois appears attributable to its low 
seed yield in this area and to the fact that its foliage is seldom found in duck gizzards here. 
food resources. A serious paucity of 
other duck food plants in 1938 may have 
accounted for its unusually high rating 
of 0.26 in that year, table 4; when other 
food resources were greater, 1939, its in- 
dex rating was less than 0.02, table 5. 
At Crane Lake in 1938, white waterlily 
rated 0.19, but it dropped to 0.01 in 
value the following year. This was 
doubtlessly due to the inhibition of 
fruiting caused by low water. The 
above data rank this species as poor 
to fair in food value, somewhat higher 
than the American lotus. 
Pickerelweed, Pontederia cordata, fig. 
14, is not given a numerical value in 
table 3. It was impossible to secure an 
index figure for this plant covering the 
3-year study period because of the in- 
finitesimal amounts of seed consumed 
by ducks. An index value of 0.03, de- 
rived from data obtained in 1939 at 
Crane Lake, places pickerelweed for that 
year and area above river bulrush and 
American lotus. If its low value is 
adequately portrayed by this small 
Fig. 14.—Pickerelweed (Pontederia cordata) 
is of doubtful value as a duck food plant in 
spite of the fact that it is one of the top-ranking 
seed producers in the Illinois River region. Its 
blue flowers and heart-shaped leaves distin- 
guish it from duck potato, which has white 
blossoms and arrowhead-shaped leaves. 
