indicates that green-wing teal duck-days dropped from a high of 286,000 

 duck-days in 1963 to a low of 12,000 duck-days in 1970 while the 

 wigeon fell gradually from a high 713,000 duck-days in 1964 to 43,000 

 in 1970. A slight increase in use has occurred during the past two 

 years . 



Lesser scaups have utilized Pools 25 and 26 more extensively than 

 Pool 24. Scaup days of use (Figures 12, 13, & 14} have shown a downward trend 

 throughout the period 1959-^-1977 . The reason for this decline is not 

 fully understood, but in the Illinois valley a decrease in food sup- 

 plies resulted in a drastic decline in scaup abundance (Mills et al. , 

 1966: 18). Anderson (1959: 317) found that lesser scaup fed on plant 

 meterial 10 percent of the time in the upper Illinois River and in 

 the Mississippi River above Pools 24, 25, and 26. The fingernail clam, 

 a major food source of the lesser scaup, was found in greater abun- 

 dance in these reaches of the two rivers than in the project area. 

 Therefore, aquatic plants are probably more important to the lesser 

 scaup diet in Pools 24, 25, and 26. The decrease of aquatic plants in 

 the late 1960 's would adversely affect the lesser scaup utilization 

 of the project area. 



The mallard has been the principal species benefited by the pool 

 impoundments and refuges. Mallard use of Pools 24, 25, and 26 has 

 been increasing in recent years (Figure 15). Although mallards are able to obtain 

 a large share of their food from waste corn left in the fields after 

 hawest, the increased water acreage is valuable as resting sites. The 

 loss of aquatic plants affected mallards less than other species; they 

 feed in shallow water primarily on seeds of moist soil plants. Federal 

 and state agencies as well as numerous private duck clubs have de- 

 veloped low leveed areas for the development of moist soil waterfowl 

 foods on areas adjacent to Pools 24-26. The presence of managed 

 waterfowl areas lateral to the project area has increased mallard use 

 in the project area. 



The wood duck is the primary breeding duck in the project ares. 

 Natural cavities found in mature timber are used by the wood duck 

 as nesting cavities. The clearing of extensive tracts of mature bot- 

 tomland forest prior to impoundment reduced the number of natural 

 cavities available for nesting. However, the increase in water levels 



155 



