334 



Illinois Natural History Survey Bulletin 



Fol. 2j, Art. 2 



offer a means of determining compara- 

 tive mortality rates among waterfowl 

 by species or by years. The ratio of the 

 number of first-year returns (bands re- 

 covered before the beginning of the 

 hunting season next after banding) to 

 the number of birds banded gives a 



used to compare mortality rates for each 

 of these three species from year to year, 

 but, because of the few species banded, 

 we cannot employ such data to compare 

 mortality rates among all the species of 

 ducks in Illinois. 



To determine the optimum dates for 



comparative, if not quite accurate, the open duck season in Illinois, it is 



I5-- 



I 

 O 



< 



I- 

 o 



Y- 



V- 

 Z 

 U 



o 5-r- 



QC 

 U 

 Q. 



-° WATERFOWL FLIGHT 



— WATERFOWL FLIGHT 

 OTHER THAN MALLARD 



1938 



I 



d 



D 

 < 



I 



lO 



K 



CL 

 U 



I 



O 



— r- 



I 

 CD 



O) 



ro 



Fig. 3. — Chronology of flight of all duck species, and species other than mallard, in relation 

 to the hunting season in the Illinois River valley, 1938. 



measure of mortality. The actual hunt- 

 ing mortality among waterfowl is higher 

 than that indicated by band returns, 

 for a recent study made by the writer 

 revealed that Illinois hunters report 

 only about two-thirds of the bands 

 taken. 



Of about 30,000 ducks banded by the 

 Illinois Natural History Survey, only 

 three species — mallard, black duck and 

 pintail — are in significant numbers. The 

 banding data we have obtained can be 



necessary first to evaluate the vulner- 

 ability to hunting of each important 

 species and the shooting pressure placed 

 upon it. Because the ducks banded in 

 Illinois do not include all species in 

 significant numbers, we have not used 

 banding data but have compared the 

 Illinois kill of each principal species with 

 its Illinois population during the open 

 season to determine its vulnerability to 

 hunting in relation to the vulnerability 

 of other species. The term vulnerability 



