May, 1943 
involved. A noticeable error occurred in 
the case of teal grass, Eragrostis hyp- 
noides, because millets, pigweed and 
other plants growing over this species 
when the areas were surveyed made it 
virtually impossible to plot. 
It may seem that the discrepancies 
enumerated above outweigh the bene- 
fits derived from this method of evalu- 
ation. However, we believe that, de- 
spite its limitations, the use-abundance 
rating gives a far more nearly accurate 
picture of the food value of a plant than 
do percentages based solely upon the 
amount of food taken. 
Because of the different factors that 
may affect the availability of seeds or 
other plant parts of a particular species 
Table 5.—Per cent of use, per cent of 
abundance, and index value of aquatic and 
moist-soil plants at certain lakes in the 
Illinois River valley, 1939. Areas included 
are listed in table 2. 
PER PER 
Cent | CENT | Inpex 
PLANT OF OR VALUE 
Lice ABUN- 
DANCE 
Walter’s millet... .. 9.37 0226 "36 04 
Ricecnt-erass.... ..: DIAS 1.47 15.13 
ENUIEO PASSES: coe asf ars 10.83 OZ 15.04 
Japanese and wild 
MiVletse ga etc! 14.82 5.44 262 
Duckrpotato . 3... 3.94 1.48 2.66 
Largeseed, nodding 
and other smart- 
WGCOSS om ies eS. O15 fi high 
SMe gusnes 04. %.).| 0.25 0.10 2G 
Buttonbush. ........ 2.64 1. 167-14 med. 
Giant bur-reed.....| 0.44 0.20 2:20 
Grol ee eee 13,62 6.28 2.19 
Marsh smartweed...| 7.75 6473 eles 
Mieaverasee oh. os... 1.54 tr; med 
Longleaf pondweed | 2.11 2.24 0.94 
Water hemp....... 1.65 IPH 0.74 
Sago pondweed..... 0.38 6.14 0.06 
American lotus... .. 0.43 25029 0.02 
River bulrush...... VEC moN ee 0.02 
Pickerelweed....... tr. 0.03 low 
Marsh mallow...... tr. 0.02 -low 
White waterlily..... th aah low 
Bret ICe.,-. st. 0.00 22 low 
Marsh cord grass...| 0.00 0.26 low 
Southern naiad..... 0.00 Oe hZ low 
Other plants.... 4.20 i 
*Other than marsh smartweed. 
because of difficulty of measurement. 
medium, +tMinimum figure. 
**kNo figure given 
tr.=—trace. med.== 
BELLROSE & ANDERSON: Duck Foop PLANTS 
421 
in any one year, it seems advisable to in- 
clude yearly tables as well as a general 
summary table. Comparisons between 
years will aid in determining the in- 
fluences of altered habitat conditions on 
the food value of plant species. 
Ratings of Food Plants Studied 
The value, as food for ducks, of the 
moist-soil and aquatic plants commonly 
occurring in the Illinois River valley is 
based on data presented in tables 3-6. 
Rice cut-grass, Leersia oryzoides, fig. 
1, outranks all other species in food 
value for the 3-year period, table 3. In 
1938 it ranked first by a wide margin, 
table 4. In 1939 it ranked second to 
Walter’s millet, table 5; in 1940 it was 
slightly behind Japanese and wild mil- 
lets combined, table 6. This variance in 
Table 6.—Per cent of use, per cent of 
abundance, and index value of aquatic and 
moist-soil plants at certain lakes in the 
Illinois River valley, 1940. Areas included 
are listed in table 2. 
PER PER 
Cenr | CENT | Inpex 
PLANT OF OF VALUE 
Wer ABUN- 
DANCE 
Japanese and wild 
muillets te aan hee 21226 Zed 7.28 
Riceleutssrass- re. Payal i! 4.15 6.92 
Walter’s millet.....| 7.64 1.63 4.68 
Largeseed, nodding 
and other smart- 
WEEUS th tin a ihn oe 9.56 3.94 2:43 
INiterasses ste. 6203 4.18 2.06 
Diuckepotato wr. 1237 1.41 0.97 
Woontally ern ene 3.60 Bals) 0.70 
Spike rushes. aulce 00S 0.13 0.60 
Button bush wee ee 0.71 2.05 0.35 
Mea larass spews eta 9. 0.08t 
Watemnemp ant eto. Osu 2 os0S 0.30 
Longleaf pondweed 1.38 3255 0.25 
Sago pondweed..... 0.38 1.58 0.24 
Marsh smartweed. . 0.73 4.06 0.18 
River bulrush...... 0.39 | 20.34 0.02 
American lotus..... 0.05 14224 0.004 
Southern naiad>...) 0.00 O22? low 
Small pondweed....| 0.00 0.20 low 
Longleaf 
Aminainiaen wea ce 0.00 0.07 low 
Others) many). 2 soc 6.00 a4 
*KNo figure given 
+Minimum figure. 
*Other than marsh smartweed. 
because of difficulty of measurement. 
