418 
measurement of the contents of 3,200 
gizzards gathered at duck clubs during 
the 1938, 1939 and 1940 hunting seasons 
(Anderson ms.). Table 1 reveals the 
numbers of stomachs and the various 
species of ducks represented. The sam- 
ple of dabbling duck gizzards 1s fairly 
proportionate to the occurrence of the 
Table 1.—Duck stomachs examined in 
the present study. 
Duck 1938 | 1939 | 1940 |ToraL 
Mallard tas) eee 619.928 |) -360 ) 1,907 
Pintail jae eee 222 | 408 39 669 
Green-winged teal. . OS as? foal — 225 
Blue-winged teal... 51 59 | — 110 
Baldpateses aes 33 49 | — 82 
Gadwall eae, oe 3 3 36 
Shoveler™s oaec...- 16 23 | — 39 
GanvasDack seas 14 1 — 15 
Rinoneck wena 72 9; — 81 
Lesser Scallnaan ee 2 1 a= 5 
Other ducks... 2 17 10 6 33 
‘Lotal ee eee 1,147 |1,648 | 405 | 3,200 
different species of this type of duck in 
the Illinois River region. The sample of 
diving duck gizzards is not adequately 
representative of the occurrence of this 
waterfowl group in the region. 
Considered in this paper are only un- 
cultivated aquatic and moist-soil plants. 
Corn, usually an important duck food 
plant in the Illinois River valley, is not 
included in the calculations. 
Per cent of abundance data are based 
upon the surface area in acres of the 
aquatic and moist-soil beds at the vari- 
ous lakes studied; this area in each case 
ILLInoIs NATURAL History SURVEY BULLETIN 
Vol..22; Art.5 
was obtained by plotting the vegetation 
by aspection and rough triangulation on 
large scale base maps and using a pla- 
nimeter to measure the area covered by 
each species (Bellrose 1941). Table 2 
gives the total area of aquatic and moist- 
soil vegetation for the lakes considered 
in this paper, and the number of gizzards 
examined from each area. 
An index rating of 1.0 for a food plant 
indicates that this plant was used ap- 
proximately in proportion to its abun- 
dance. The larger the figure, the greater 
is the value of the plant species as a duck 
food. Conversely, the smaller the figure, 
the lower is the value of the species. 
We do not wish to pretend that the 
index figures listed here are the final and 
absolute evaluation of the food plants 
enumerated. Habits of waterfowl, plant 
differences, plant habitat characteristics, 
and inaccuracies in determining abun- 
dance of vegetation are factors tending 
to prevent minutely exact rating figures. 
Ducks killed at any one lake may or 
may not have obtained their last meal 
there. Plant items in stomachs and 
banding data reveal that occasionally 
ducks have fed 10 or 100 or more miles 
from the place in which they are shot. 
Food habits of various species of 
ducks differ widely, too, so that coon- 
tail may rank high at a certain place be- 
cause of presence of many baldpates 
and gadwalls, or nutgrasses and pig- 
weeds may rank high at another place 
because pintails and teals are abundant 
there. 
In some instances changes in the rank- 
ing of a plant from year to year are due 
Table 2.—Number of acres of duck food plants at various lakes in the Illinois River 
valley and the number of duck stomachs examined from each area. 
1938 1939 1940 
AREA 
Acres of | Number of | Acres of | Number of | Acres of | Number of 
Vegetation | Stomachs | Vegetation | Stomachs | Vegetation | Stomachs 
Duckslsland see eee 1,255 207 1,539 162 — — 
Clear and Chautauqua 
Lakest2As we tems sees 1,441 358 De022 531 2,389 134 
Craneilake. eo ee 425 293 466 342 S35 142 
Gubatisiland #...). a gs de 329 289 441 355 — — 
Douglas Lakewos e = — 1,686 98 — — 
(Goose, Pond sane 3 a 908 160 968 129 
‘Wiens Je, Bo Ace 3,450 L147 7,062 1,648 3,888 405 
