drastic reduction occurred solely in the Illinois River 

 valley (Fig. 15). 



The lower mallard population in Illinois following 

 1955 is attributed almost entirely to loss in production 

 resulting from drought on the northern plains breeding 

 grounds. The decline in mallard numbers in Illinois did 

 not parallel the loss of aquatic plant and animal food 



resources. The mallard in Illinois feeds mainly on waste 

 corn and the seeds of moist-soil plants (Anderson 1959) : 

 its sustenance is more stable, being to a large extent in- 

 dependent of animal life or aquatic plants. 



Mallards have sufTered a greater diminution because 

 of drought on the northern plains than have most of the 

 diving ducks; lesser scaup and ring-necked ducks in 



CANVASBACK 



010= ILLINOIS RIVER VALLEY 

 ■ = MISSISSIPPI RIVER VALLEY 



168,000 



!^ I40P00- 



lE 



lU 



o. 



Q 112,000- 



84,000- 



56,000- 



< 28,000 



1946 '47 '48 '49 '50 '51 



Fig. 13. — Canvasback duck 

 aquatic vegetation and mollusca. 



52 53 54 55 '56 



58 



60 



populations declined drastically in the 

 (Illinois Natural History Survey data.) 



61 62 63 64 

 Illinois River 



m 



alle 



1946 lo 1954 

 following the near disa 



1955 to 1964 

 ppearancc of 



RUDDY DUCK 



72,000 



u 60,000- 



o 



Ul 



i 48,000 



£ 36,000 



s 



Z 

 -I 



? 24,000 



12,000- 



\ \ 



El = ILLINOIS RIVER VALLEY 

 ■ = MISSISSIPPI RIVER VALLEY 



1946 47 48 '49 '50 



36,000-1 



Si; 30,000 



a 24,000 



18,000- 



12,000- 



< 6,000- 



I 



l»46 10 1954 



1965 10 1964 



lig. II. — Ruddy ducks feed on both .small mollusca and aquatic in.srct larvae. Because aquatic insect lar\ac did not decline in 

 abundance so much as the mollusca, these ducks persisted in greater numbers, proportionately, after 1954 than did other diving ducks. 

 (Illinois Natural History Survey data.) 



20 



