46 LEADPOISONING 



ground may be completely dried and thus become unattractive to birds 

 in midsummer. Inadequate water supply and fluctuating water levels 

 are the chief causes of outbreaks of duck sickness. These are often the 

 result of the diversion of water by man where formerly nearly constant 

 water depths were maintained throughout periods of hot weather. "Un- 

 less these conditions can be restored, duck sickness will continue to take, 

 ever increasingly, its annual devastating toll of western wild fowl." 



LEAD POISONING 



All birds of the family Anatidae require certain quantities of gravel 

 or grit for the necessary grinding of food in the gizzard and, in seeking 

 this essential substance, will swallow any small, hard objects they en- 

 counter while feeding. Large quantities of lead shot are deposited every 

 year about shooting points and blinds in shallow bays and marshes, and 

 are taken in surprising numbers by the feeding wild fowl. Lead poison- 

 ing results, and is so deadly in its effect that it is proving to be a factor 

 of considerable importance in the decline of our waterfowl. 



As a result of investigations into the poisoning of waterfowl by 

 lead, Wetmore (1919) says: "It was found that six pellets of No. 6 shot 

 constituted an amount of lead that was always fatal. Two or three shot 

 were sufficient to cause death in several instances, and as the number was 

 increased the resistance of individual birds decreased. In one experi- 

 ment two Mallards were each given one No. 6 shot. One died 9 days 

 later, while the other was able to throw off the effects of the lead and 

 recover. Pintails and Redheads were similarly affected. One male Pin- 

 tail was given four pellets of No. 6 and another six. Both died, the for- 

 mer in 11, and the latter in 13 days. One Redhead was killed by taking 

 six No. 6 shot. Another was given four pellets of shot and was sick for 

 some time, but finally recovered." 



Describing postmortems on ducks that had died of lead poisoning 

 the same writer says: "The usual number of shot in one stomach was 

 15 to 40. The largest number of pellets taken from one bird was 76, 

 found in the gizzard of a Mallard secured near the mouth of the Bear 

 River, Utah. In September, 1916, during routine laboratory work, 28 

 Mallards and 10 Pintails that had died from lead poisoning were exam- 

 ined. From the stomachs of these 38 birds 939 shot were recovered, an 

 average of a fraction less than 25 each." Cottam (1939) referring to 

 Canvas-backs, says: "Lead shot pellets are sometimes picked up by these 

 ducks as they feed. This is altogether too common an occurrence in 

 baited areas where large numbers of shot are expelled over a limited 

 area where the birds repeatedly feed, with the result that large numbers 

 of birds experience a lingering death and that those that do recover 

 probably become sterile. The writer found 96 shot (lead pellets) in a 

 single gizzard of this species." Referring to 177 Lesser Scaup taken dur- 

 ing a gunning season, the same writer says: ". . . .it was found that 

 365 (more than 76.5 per cent) had consumed a total of 4,191 lead pellets 

 an average of 11.5 shots per bird and that individual stomachs con- 

 tained from 1 to 58 pellets." 



