December, 1958 



Scott: Wildlife Research 



193 



dealt with duck food plants. A study of 

 the ecology of aquatic and marsh plants 

 revealed the relationships of fjuctuatinji 

 water levels and turbidity to plant 

 growth (Bellrose 1941). As a result of 

 this study, two techniques for production 

 of duck foods were recommended : ( 1 ) 

 dewaterino; certain areas to encoura^^e 

 growth of moist-soil plants on exposed 

 mud flats and (2) stabilizing; water levels 

 at depths of 2 to 3 feet to promote jj;rowth 

 of aquatic plants. 



A stud\ of the relative value of various 

 plants as duck foods (Bellrose & Ander- 

 son 1943:432-3) showed that moist-soil 

 plants, such as rice cut-grass, millets, 

 smartweeds, and nut^^rasses, were much 

 more valuable as duck foods than such 

 aquatic and marsh plants as the pond- 

 weeds, coontail, duck potato, and bur-reed. 

 This stud\ is believed to be the first in 

 which the food habits of waterfowl were 

 related to food availabilitv. Later, a 

 study by Low & Bellrose (1944:21) re- 

 \ealed that, among 28 waterfowl food 

 plants, 6 of the 7 heaviest seed producers 

 were emergent or moist-soil plants. 

 Harry G. Anderson (unpublished MS) 

 made a little known but substantial con- 

 tribution to knowledge of the diet of 

 ducks in Illinois when he analyzed and 

 reported upon the contents of 4,977 giz- 

 zards of ducks, representing 17 species, 

 taken during the hunting seasons in 1938, 

 1939, and 1940. 



In a sense, Illinois is at the bottleneck 

 of the Mississippi Flyway, the fiyway 

 with the largest population of ducks in 

 North America. The resulting constric- 

 tion of duck populations streaming into 

 Illinois has provided a remarkably fine 

 opportunity for study of flyway popula- 

 tions. A comprehensive investigation of 

 sex and age among ducks, covering 1939 

 through 1954, has been completed (Bell- 

 rose, Hawkins, Low, 5: Scott unpublished 

 MS). From 1938 through 1958, periodic 

 censuses have been taken of waterfowl 

 populations in the Illinois River valley 

 during fall, winter, and spring. In 1946 

 the census route was expanded to include 

 the Mississippi River valley between 

 Rock Island and Alton. These censuses 

 have provided information on the effect 

 of weather, water levels, food, and 

 refuges upon waterfowl populations. 



A 5-year investigation of duck popula- 

 tions and kill by hunters revealed that 

 "altering the length of the season is one 

 of the most expedient wavs to regulate 

 the duck kill" (Bellrose 1944:371). The 

 most desirable dates for waterfowl hunt- 

 ing seasons of various lengths in Illinois 

 were determined (Bellrose 1944:371): 



For a 30-day season, November 1-30; for a 

 45-day season, October 22-December 5; for 

 a 60-day season, October 10-December 8; 

 tor a 70-day season, October 1-December 9; 

 for an 80-day season, September 26-December 

 14; for a 100-day season, September 20- 

 December 28. 



A studv of flvwav refuges in Illinois 

 (Bellrose' 1954:169) led to the conclu- 

 sion that they were of value both to 

 waterfowl and to hunters. Flyway 

 refuges permitted waterfowl to rest along 

 the flyway during the hunting season and 

 placed more food within their reach, 

 thereby conserving food resources on the 

 wintering grounds. Waterfowl concen- 

 trating on the refuges fed in fields and 

 marshes within their daily cruising range. 

 Thus, the refuges provided for holding 

 local concentrations of ducks which could 

 be shot when they flew out to feed. 



One of the most impressive duck flights 

 in a decade swept through Illinois on 

 November 2, 1955 (Bellrose 1957). It 

 was determined that most of the birds in 

 the flight left Canada on November 1 

 and moved so rapidly that some reached 

 the Gulf of Mexico by the morning of 

 November 3. This mass migration of 

 waterfowl was evaluated bv Bellrose 

 (1957:24) as follows: 



Low pressure areas in Canada resulted in a 

 southward flow of a mass of Continental 

 Arctic air. The low temperatures resulting 

 from Continental -Arctic air triggered the 

 flight from the Great Plnins of Canada and 

 the I'nited States. 



Over 75,000 ducks, largely mallards, 

 have been banded by Natural History 

 Survey investigators at four widely sepa- 

 rated localities in the state. Recoveries 

 from some of the bandings were used in 

 calculating the annual mortality of the 

 mallard, black duck, and blue-winged 

 teal (Bellrose & Chase 1950). Of the 

 three species, the mallard proved to have 

 the lowest mortality rate, and this 

 "amounted to 55 out of 100 birds the 



