11 



VALUE OF POOD. PLANTS STUDIED 



, The value as v;aterfowl food of" the most abundant aquatic 

 plants in the Illinois River Valley in 1938' is discussed below, 

 plant by plant. Statements . are based upon data obtained in the four 

 . study areas' nentioned above. 



RICE CUT-GRASS, L eersla oryzoide s Sv;. , in 1938 v^as appar- 

 ently the best native duck food lolant in tile Illinois River re;rion 

 with an index' rating of 39.00 for the four study areas considered as 

 a vvhole. At Cuba Island, wliere an excellent bed occurred, it rated 

 second to coontail. lerhaps there coontail v.as more abundant than 

 recorded.- In early., svttmier, many coont.ail plants were noticed at 

 Cuba Island in a large bed of marsh smartweed, but, when the vegeta- 

 tion was mapped in August, the v;ater was so low that it was virtu- 

 ally impossible to worl: a boat into the bed and ascertain t}ie extent 

 of the coontail. At Crane Lake, rice cut-grass was second to long- 

 leaf pondweed in index -rating. There only a small portion of the 

 rice cut-grass bed was available to the ducks because the birds 

 could not feed en the rootstocks of the m.any plants t].at were not 

 flooded. 



COONTAIL', Cer atop hyll^jm demers^ju n L. , was slightly below 

 rice cut-grass in actual use, but, since ft was much more a.bundant, 

 its index rating for the f.^ur study ai-eas considered as a whole was 

 only 1.68. ' This species grew almost exclusively in areas with 

 stable .or semistable water levels. Of the four areas studied, the 

 best, for demonstrating the value of coontail was -Duck Island, where 

 this species was first in value, v^ith an index rating of 10.24. In 

 t}ie Clear Lake region, coontail had a lower index rating than duck 

 potato or marsh smartv^reed. 



NUTGRASSES, Cyperus erythrorhizos Muhl . , Cyperus s trigosus 

 L. , and Cyperus esculentus L. , forr,ied 11.73 per cent of all native 

 duck foods in the- gizzards examined; yet in 1938 these species oc- 

 curred only as sm.all" patches in a few }. laces in the four' areas from 

 which gizzards wore' oollocted. How was it lossible for ducks to ob- 

 tain such a large volume of food from t]'.ose small-seeded spe'cies? 



In 1938- a large per cent of the waterfowl on the study 

 areas fed on mud flats as well as in shallow laku water. No plants 

 were seen growing on' the mud f lats--exposed areas of the shallDv; 

 lake basins. In the two preceding years, 1936 and 1937, " because the 

 water had receded early in the summer, nutgrasses (as' well as sm_art- 

 weeds, v;ater hemp and teal grass) formed luxuriant beds on tlie mud 

 flats. The conjecture was made that large quantities of seed 

 dropped by the 1936 and 1937 crops of these plants furnished food 

 for ducks in 1938. . • 



To substantiate or disprove this conjecture, several mud 

 samples were collected froi.i barren mud flats in September, 1940, 

 three ;^'ears after moist soil plants had grown on these areas. These 

 sam^-lcs, collected from. IS square .feet of- surface, yielded 2,500 

 seeds of Cyperus erythrorhizos • and 2,000 seeds of C. strigosus . The 

 above evidence, we believe, lends strong support to tie statement 

 that Cyp erus seeds fo-und in duck stomachs in 1938 were from 1936 and 

 1937 croiTs^"" 



