May, 1943 
BELLROSE & ANDERSON: Duck Foop PLANTs 
427 
Fig. 11.—Longleaf pondweed (Potamogeton americanus) ranks eleventh among Illinois River 
valley plants as a source of duck food. 
produces more seed. 
value, but below the nutgrass group. 
Seed production studies (Low & Bell- 
rose ms.) revealed that in 1941 teal 
grass produced about half as much seed 
as Cyperus erythrorhizos and almost as 
much as did duck potato per area unit. 
Duck potato, Sagittaria latifolia, fig. 
9, has an index value, table 3, about two- 
fifths as great as that of giant bur-reed. 
Incidentally, in 1941, bur-reed pro- 
duced about two-fifths more seed per 
unit of area than did duck potato. For 
the most part, the large tubers of duck 
potato, often a foot or more under- 
ground, are not available as duck food. 
However, at times canvasbacks and 
ringnecks have succeeded in obtaining 
numerous tubers, which considerably 
raised the value of duck potato for cer- 
tain areas. 7 
Marsh smartweed, Po/ygonum Muh- 
lenbergi1, fig. 10, has in table 3 an index 
value of 0.84, which places it slightly 
below duck potato. Beds. of this spe- 
cies will not produce seed when growing 
out of water; optimum production oc- 
curs in water 12 to 18 inches deep. In 
several areas, beds produced no seed be- 
It ranks above sago pondweed apparently because it 
cause of a lack of water. This species 
would rank somewhat higher if all the 
beds that failed to produce seed were ex- 
cluded from the calculations. 
Longleaf pondweed, Potamogeton 
americanus, fig. 11, ranks below marsh 
smartweed in index value, table 3, de- 
spite the fact it outproduces the latter in 
seed yield by a wide margin. This may 
indicate that, because of the greater 
depth of water at which the plants grow, 
seeds of aquatic plants are less accessi- 
ble to dabbling ducks than are those of 
marsh plants. 
Buttonbush, Cephalanthus occtden- 
talis, seldom grows in the areas that 
were mapped, occurring usually as a 
part of, or within, the shoreline. 
Since it is also a woody species, its 
abundance was not determined for most 
areas. However, in the Crane Lake 
region, its abundance was determined in 
1939 and 1940. When there was a 
dearth of other duck foods in this area, 
1939, the index rating was 0.94; when 
there was an abundance of other foods, 
1940, the index rating dropped to 0.12. 
A study of the food consumption on 
