May, 1943 
toms; most of the seeds fall a month be- 
fore the greatest numbers of ducks ar- 
rive. McAtee (1939, p. 33) in comment- 
ing on the value of wild rice states: 
“This plant has a great reputation as a 
producer of food for wildfowl—too high 
a rating, perhaps, considering its local 
and seasonal availability.”’ 
Small pondweed, Potamogeton pusit- 
/us, is another species that is generally 
Fig. 16.—Wild rice (Zizania aquatica) is not 
a valuable duck food plant in the Illinois River 
valley; few of the seeds are available during the 
season of the principal waterfowl flight in the 
fall months. 
considered a good waterfowl food plant. 
Although it amounted to 0.05 per cent 
of the vegetation, table 3, no foliage or 
seeds were found in any of the stomachs 
analyzed. Studies of seed yield in 1941 
(Low & Bellrose ms.) revealed that it was 
one of the lowest producers. We have 
noted that the BeEctaute parts, aiter 
fruiting time in late July and early 
August, generally disintegrate. Whether 
disintegration is caused by green algae, 
by the competition of coontail and 
southern naiad, or by some unknown 
factor, we do not know. 
Longleaf ammannia, 4mmannia 
coccinea, is a moist-soil plant that has 
occurred fairly abundantly at Clear 
Lake. No evidence was obtained that 
this species was ever used as food by 
ducks, table 3. 
Plant parts of a large number of other 
species were consumed in infinitesimal 
amounts; likewise some other species 
BELLROSE & ANDERSON: 
Duck Foop PLANTS 431 
were found in the field in amounts too 
small to tabulate, table 3. 
Discussion 
That the true value to waterfowl of 
the various aquatic and moist-soil plants 
cannot be determined solely from the 
use made of them by the birds is evident 
after consideration of a few outstanding 
instances. Based solely on use, Walter’s 
millet ranks sixth in value among duck 
food plants of the Illinois River valley, 
slightly below marsh smartweed, table 3. 
When abundance as well as use is con- 
sidered, Walter’s millet is second in 
rank, nearly 13 times as great in value 
as marsh smartweed, which places 
ninth in value, table 3. In another in- 
stance, based on use only, coontail ranks 
second, three-fifths as valuable as the 
leading rice cut-grass; however, after 
the abundance figure is_ considered, 
coontail drops to seventh place, with 
about one-seventh the value of rice cut- 
grass. Giant bur-reed, according to use 
made by ducks, ranks sixteenth in value. 
When the meager occurrence of the bur- 
reed is taken into consideration, it 
jumps to sixth 1n value. 
Although many extraneous and di- 
verse factors have prevented us from 
obtaining exact values for duck food 
plants, we believe that, by considering 
both the abundance and use of such 
plants, it is possible to ascertain more 
nearly the true value of plant species, as 
food for waterfowl, than by using data 
based solely on the quantity of the 
items taken. 
What determines the duck food value 
of various aquatic plants? Logically, 
availability and palatability are two 
most important factors. We _ believe 
evidence discussed in this paper shows 
that availability, as measured by food 
yield and accessibility, determines the 
value of most plants generally con- 
sidered as sources of duck food. It 
should be noted that, in many species, 
seed yield and value go hand in hand. 
In other species, depth of water evi- 
dently affects availability, through mak- 
ing the food source less, or more, easily 
accessible to ducks, especially dabbling 
ducks. We may tentatively assume that 
seeds of moist-soil plants are more 
