346 



Illinois Natural History Survey Bulletin 



Vol. 2j, Art. 2 



60 



40 

 20 



WATERFOWL 

 CENSUS 

 ILLINOIS RIVER 

 1938 



AUGUST 



SEPTEMBER OCTOBER 



NOVEMBER 



DECEMBER 



JANUARY 



Fig. 11. — Polygons, based upon number of birds per acre of water surface in the Illinois 

 River valley in 1938, showing the chronology of flight of 11 species of waterfowl in relation to 

 the hunting season. 



