340 



Illinois Natural History Survey Bulletin 



Vol. 2j, Art. 2 



for open water hunters, table 2. Be- 

 cause of their aversion to crossing 

 marshes or timbered necks of land, they 

 do not furnish many targets for shore 

 and marsh hunters. Club hunters in 

 Illinois seldom resort to open water 

 gunning, but where this type of hunting 

 occurs, as at the Sparland Public Shoot- 

 ing Ground, large proportions of the 

 ruddies present are taken (Bellrose 

 1944). 



Proportionally more ring-necked ducks 

 than ruddies were bagged by club hunt- 

 ers in the years of this study, table 2. 

 There can be little doubt that much of 

 the difference in vulnerability between 

 blackjacks, as ring-necked ducks are 

 often called in Illinois, and the lesser 

 scaups resulted because blackjacks in- 

 habit small bodies of water and marshy 

 or inshore areas of large lakes instead 

 of open water, and are more likely to 

 pass under the muzzles of guns than are 

 bluebills, as lesser scaups are sometimes 

 known. The greater fondness of ring- 

 necks for shoal water is reflected in their 

 food habits; Cottam (1939) reports 

 81.47 per cent of the ring-neck's food 

 consists of aquatic plants, about the 

 same per cent as is found in the can- 

 vasback's diet, whereas only 59.55 per 

 cent of the lesser scaup's diet is made 

 up of aquatic plant items. 



Evidence obtained in 1941 and 1942 

 indicates that redheads are much more 

 readily bagged in proportion to the 

 population than are ring-necked ducks. 

 I believe that redheads are the least 

 wary of the Nyroca, the most important 

 group of diving ducks. They decoy 

 more readily in Illinois to blocks than 

 other members of the genus, but whether 

 this is due to their flying in small flocks 

 or to lack of wariness, or to both, is 

 uncertain. In Illinois, redheads fre- 

 quent marshy lakes and the inshore of 

 large lakes more than any other diving 

 ducks with the possible exception of the 

 ring-necks. Cottam (1939) reports the 

 food of the redhead to be 89.66 per cent 

 vegetable material; this is the largest 

 proportion of plant items in the diet 

 of any diving duck important in Illi- 



nois. 



Because of differences in flocking 

 and feeding habits, types of habitats in 

 which they are hunted and methods by 



which they are hunted, the ducks dis- 

 cussed above may not have the same 

 relative vulnerability to the shotgun 

 throughout North America. However, 

 the ratings determined by this study 

 show which species are in need of the 

 most protection in Illinois, and probably 

 they may serve as useful indicators of 

 the species that are most likely to suffer 

 from overshooting in the Midwest. 



Observations made in 1943 on Grass 

 Lake, in northeastern Illinois, suggest 

 that coots may be more readily killed 

 than ducks (Bellrose 1944). Careful cal- 

 culations indicate that, on the opening 

 day of the hunting season, 18,225 coots 

 and 108 ducks were killed. These 

 figures represent about 95 per cent of the 

 coot and 15 per cent of the duck popu- 

 lation then present. The ducks that 

 made up the bulk of the population on 

 Grass Lake were blue-winged teals, con- 

 sidered highly vulnerable in comparison 

 with most other duck species. 



Influence of Open Season. — Be- 

 cause duck species differ from each 

 other to some extent in the chronology 

 of their migration, figs. 8-10, if the rel- 

 ative vulnerability of species is known 

 the opening and closing of the hunting 

 season may be adjusted to lift some or 

 all of the shooting pressure from the 

 most vulnerable species, or those most 

 needing protection. 



Leopold once wrote (1933) that a 

 number of states purposely set the open 

 season on deer late in the year so that 

 severe weather will keep all but the 

 hardiest hunters at home. He also 

 remarked that several states, including 

 Michigan, open the season on prairie 

 chickens at a late fall date to take ad- 

 vantage of the fact that these birds are 

 harder to kill late than early in the 

 autumn. 



How have the open seasons from 1938 

 through 1942 influenced the duck spe- 

 cies that migrate through Illinois? We 

 have attempted to answer this question 

 by comparing the vulnerability quo- 

 tient with the mortality quotient for 

 each important species to obtain what 

 we have termed the shooting pressure 

 quotient. This shooting pressure quo- 

 tient gives a comparative evaluation of 

 the effect of the open season on im- 

 portant duck species in Illinois for the 



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