348 



Illinois Natural History Survey Bulletin 



Vol. 2j, Art. 2 



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WATERFOWL 

 CENSUS 

 ILLINOIS RIVER 

 1 940 



AUGUST 'SEPTEMBER ' OCTOBER ' NOVEMBER ' DECEMBER 



JANUARY 



Fig. 13. — Polygons, based upon number of birds per acre of water surface in the Illinois 

 River valley in 1940, showing the chronology of flight of 12 species of waterfowl in relation to 

 the hunting season. 



J 



