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A Review of the Problem of Lead Poisoning in Waterfowl

Practices to Reduce Lead Toxicosis


Manipulation of the Habitat

Several ways of manipulating the habitat to reduce lead poisoning in waterfowl have been considered. Osmer (1940) suggested distributing gravel to be used as grit by waterfowl. In winter, the gravel could be placed on the ice. Beer and Stanley (1965) reported that when grit is limited, lead pellets are more likely to be ingested and are retained longer than when grit is plentiful. Trost (1981:70) also surmised from his study of grit passage that ducks deprived of grit retain shot longer than ducks with access to grit. Although they presented no supporting evidence, Osmer (1940), Rosen and Bankowski (1960), and Beer and Stanley (1965) suggested that excess grit moves through the gastrointestinal tract of birds quickly and carries eroded lead pellets with it. Sanderson and Irwin (1976:39, Table 38) noted a significantly higher expulsion rate of lead pellets from game-farm mallards with access to soil 1 to 7 days after dosing as compared with ducks on a wire floor. The diet for both groups was shelled corn. From 7 to 21 days after dosing, ducks with access to soil continued to pass shot more quickly than did ducks on wire, but the differences were not significant. Balanced against the expulsion rate, however, was the increased erosion rate of the ingested shot among ducks with access to soil. The daily erosion rate of lead from ingested pellets was significantly higher 1-7, 8-14, and 15-21 days after dosing in ducks with access to soil than it was in ducks on wire. The presence of soil or grit, or both, results in a higher daily exposure to eroded lead in ducks before the pellets are expelled or entirely eroded. Thus, the total effect of readily available grit on mortality from ingested lead is unclear. In individual ducks that expel ingested lead shot quickly, perhaps as a result of a readily available supply of grit, the grit may be beneficial. In ducks that do not quickly expel ingested lead shot but erode it faster because of abundant grit in the gizzard, the grit may prove deleterious (Sanderson and Irwin 1976:39).

Jordan and Bellrose (1951) reported modest success in reducing lead ingestion by using scare devices after the hunting season to drive waterfowl from heavily shot areas. Chupp and Dalke (1964) reported that attempts to drive swans from an area in Idaho polluted by lead from mine wastes were generally unsuccessful.

Losses of waterfowl to lead poisoning have been reduced in some cases by lowering water levels in feeding grounds after the hunting season so that the ducks will leave. Bishop (1972-1973) reported that water levels have sometimes been kept low in Iowa in the spring and sections of the area disked to make lead shot less available to feeding waterfowl when the area was reflooded. When ducks are discouraged from using waterfowl habitat except in hunting season, however, the value of that habitat is largely lost to waterfowl. Further, much waterfowl habitat cannot be drained, flooded, or disked between the time of lead deposition in the fall and the time ducks migrate north the following spring. Disking is not possible in areas that cannot be drained, in green tree reservoirs, and in various other habitats.

Szymczak and Adrian (1978:305) found that lead pellets on the surface of farmland near goose hunting pits in Colorado were most numerous in an alfalfa field that had not been plowed for several years. They also observed that corn and winter wheat fields on which there had been heavy shooting had comparatively high densities of pellets. Turk's Pond, the rest area for the geese in this study, did not contain significant densities of lead pellets. Szymczak and Adrian concluded that the large-scale mortality of Canada geese that had occurred in this area resulted from lead pellets ingested from agricultural fields. Fredrickson et al. (1977) found that shot pellets were redistributed by cultivation: 45 percent of the total were in the upper 5 cm (2 inches) of cultivated soil samples; 66 percent, however, were found in the upper 5 cm of uncultivated soil samples. Esslinger (1979) reported an 86-percent reduction in the number of lead pellets in the top 2.5 cm (1 inch) of soil under normal farming operations. Thus, the availability of lead to birds, including waterfowl, on heavily shot upland fields may be reduced, but not eliminated, by plowing and disking.

Jordan and Bellrose (1950, 1951) suggested management practices that encourage the growth of submerged, leafy aquatic plants for duck food because these plants provide more protection against lead poisoning than other types of natural plant foods. This practice, however, is not feasible for much of the waterfowl habitat in Illinois and elsewhere because siltation has decreased the water depth in some areas and reduced the penetration of sunlight in others so that only in limited areas can submerged aquatic plants be supported. In addition, most large-scale impoundments do not offer suitable habitats for aquatic plants.

Few success stories can be cited in which management practices have significantly reduced lead poisoning. As long as lead shot continues to be used for hunting waterfowl, it seems prudent to keep the boundaries of refuge areas constant year after year so that rest areas will remain free of lead shot. On many state and federal waterfowl refuges, however, areas opened and closed to hunting are rotated, a practice that spreads the availability of shot to feeding waterfowl.

The Case for Steel Shot

The only management practice, other than closing the waterfowl hunting season, that will eliminate waterfowl deaths caused by ingested shot is the substitution of nontoxic shot for lead shot. At present, the only proven nontoxic shot available is steel. Sanderson and Irwin (1976) reported that five No.4 steel shot ingested by captive game-farm mallards caused no significant changes in body weights compared with nondosed control birds, l, 3, and 6 weeks after dosing. Packed cell volume and hemoglobin concentrations in the blood of these birds also remained at comparable levels.

Losses due to crippling
As early as 1978 Roster (1978b:26) argued the case for steel shot: "Although steel shot can bag ducks as well as lead shot can, the belief persists that steel shot will cripple more waterfowl and damage shotguns. This belief stems from ignorance of the results of tests to investigate gunbarrel damage as well as from ignorance of the ballistic properties of steel shot. Ballistically, steel shot can be loaded to perform as well as lead shot in bagging waterfowl out to seventy yards. Steel shot retains its shape better than lead shot does, and compensations can be made for its lighter weight, enabling it to retain energy as well as lead shot." Nevertheless, waterfowl hunters continue to voice objections to steel shot. A primary objection is based on the belief that a greater number of ducks are crippled (mortally wounded and unretrieved) by steel shot than are poisoned and crippled by lead shot (National Wildlife Federation 1985b). In an Ohio survey, 45 percent of the hunters cited this reason for their opposition to steel shot (Smith and Townsend 1981). In Colorado, hunters of Canada geese feared that crippling losses would increase if steel shot were used (Szymczak 1978). Waterfowl hunters in California also identified crippling as their principal objection to steel shot (Leach 1980).

No single uncontroversial way to present data on the crippling of waterfowl has been devised. Methods commonly used include birds lost per shot fired, per bird bagged, per hunter party per day, per blind per day, and per man-day of hunting. Birds lost per bird bagged would be an appropriate method if all hunters obtained their bag limit each trip, a condition that is rarely the case. Hebert et al. (1984:395) did not analyze cripples per bird bagged in their Louisiana study because of instances in which ducks were crippled but none was bagged. The remaining three methods have reasonably uniform bases; however, the number of hunters per party, the number of hunters per blind, and the hours hunted per man-day are all subject to variation. We chose a method based on birds lost per 100 shots fired because data from all field tests that have been conducted could be handled in that fashion. We also would have presented crippling losses as birds lost per hunting party per day, per blind per day (blind-day), per man- day of hunting, or other expressions of hunting effort if these figures could have been calculated for all studies cited in Table 8; this was not the case. The only calculations possible for all five studies were birds lost per shot fired and birds lost per bird bagged; we chose the former method for the reasons cited above.

The results of several intensive field-shooting experiments that compare the effectiveness of lead and steel loads are shown in Table 8. These data indicate crippling losses in ducks and geese under actual shooting conditions in the field. No statistically significant differences were found among the three duck studies in cripples (birds lost) per shot fired for steel and lead shot. The smallest differences between lead and steel loads occurred in Missouri (Humburg et al. 1982) and in Michigan (Mikula et al. 1977), and the greatest difference was found in Louisiana (Hebert et al. 1984).

Viewing these crippling losses within the context of the national bag of ducks and recent crippling losses, however, provides a broader perspective. The national bag and crippling losses of ducks (data based largely on the use of lead shot) has averaged 12,810,600 ducks bagged per year and 2,729,000 ducks crippled (21.3 percent of the bag) for 1974-1983 (compiled from Carney et al. 1976, 1978, 1979, 1980, 1981, 1982, 1983, 1984; Schroeder et al. 1975; Sorensen et al. 1977). We can use these figures to estimate the magnitude of change that might be expected if steel shot were used for hunting ducks. Our estimates are based on the assumption that hunters will fire the same number of steel shot shells as they have of lead, an assumption that may not be valid because Anderson (1979) found that hunters fired more steel than lead shot shells. In addition, data in Table 8 suggest that hunters will bag fewer ducks with steel shot if the same number of shots are fired. In spite of these limitations, the data in Table 8 suggest that little or no difference between crippling losses with steel and lead shot would be found nationwide.

Based upon the data reported in the three duck shooting studies, the largest decrease in crippling losses that might be anticipated if steel shot were used is 5.3 percent (comparison of No. 4 lead with No. 4 steel in Michigan, Table 8). Data from the Missouri study comparing No. 4 steel with No. 4 lead loads suggest than an increase of crippled ducks (7.3 percent) would occur with steel. The largest increase in crippling losses from steel was found in the Louisiana study - 14.3 percent.

Table 8 - Intensively monitored field-shooting experiments comparing lead and steel loads for waterfowl hunting.

         
Birds Lost/100 Shots
Area
Investigator
Shot Load
Birds Bagged/100 Shots
Shots/Bird Bagged
Number
% ± steel compared with lead
Union County, Illinois
Anderson & Sanderson 1979a
#2 lead
19.5
5.1
7.0
-
 
 
#1 steel
17.9
5.6
5.4
-22.8
 
 
BB steel
20.7
4.8
5.7
-18.6
Tule Lake, California
Smith & Roster 1979b
lead
16.8
6.0
7.6
-
 
 
steel
15.6
6.4
8.1
+6.6
Shiawasse, Michigan
Mikula et al. 1977c
#4 lead
23.9
4.2
3.8
-
 
 
#4 steel
18.6
5.4
3.6
-5.3
Shell-Osage, Missouri
Hamburg et al. 1982c
#4 lead (buffered)
17.7
5.6
4.2
-
 
 
#4 lead
19.5
5.1
4.1
-
 
 
#4 steel
17.4
5.7
4.4
+7.3 d
 
 
#2 steel
17.8
5.6
3.9
-4.9 d
Lacassine, Louisiana
Hebert et al. 1984c
#6 lead
15.0
6.7
4.2
-
 
 
#4 steel
10.6
9.4
4.8
+14.3
aModerately large interior Canada geese.
bSmaller Canada geese.
cDucks
dCompared with #4 unbuffered lead.

Data from three comparable studies, therefore, suggest that the use of steel shot could produce changes in crippling losses that range from a relatively minor decrease in the number of crippled ducks to a relatively minor increase. Where within this range might we anticipate that losses from steel loads would occur if the use of steel shot were implemented across the nation?

On the basis of shots fired per duck bagged, Louisiana hunters fired more shots than hunters elsewhere, whether they used lead or steel (Table 8). Indeed, the number of lead shots fired per duck bagged in the Louisiana experiment (6.7) is above the national average of 6 (U.S. Fish and Wildlife Service 1976). Part of this difference may be aim error and part may be due to the greater difficulty of retrieving downed ducks in the high, dense marsh vegetation surrounding the shooting sites at Lacassine NWR (Hebert et al. 1984:392). Only a small proportion of wetlands in the United States possesses such vegetation. Michigan's Shiawassee River State Game Area (Mikula et al. 1972:443) and Missouri's Schell-Osage Wildlife Management Area consist of flooded timber and marsh. About 30 percent of Shiawassee also contains flooded cropland. Although no single typical shooting marsh exists, Shiawassee and Schell-Osage are more nearly representative of hunting habitats in the United States than is the Louisiana site. National estimates based on the increase (14.3 percent) of crippling losses shown for steel shot in the Louisiana study might well prove high, and estimates based on the more modest increase in crippling losses - or the decrease in crippling losses in Michigan and Missouri - might be more accurate.

The two field-shooting experiments with geese shown in Table 8 involved the moderately large interior Canada goose in Illinois (Anderson and Sanderson 1979) and smaller geese in Tule Lake, California (Smith and Roster 1979). Neither study reported significant differences between crippling rates for lead and steel shot. Extrapolating data from these two studies, we find that No. 1 steel shot would reduce crippling losses in large geese by 22.8 percent, and BB steel shot would reduce crippling losses by 18.6 percent. With midsized and smaller geese, steel shot would increase the current crippling loss by 6.6 percent. For all geese, steel shot would seem to reduce crippling losses slightly over the losses that might be expected with lead shot.

Again, viewing these losses against the national bag of geese and against recent crippling losses gives a clearer picture of what is at stake. Between 1974-1983, the national bag of geese averaged 1,757,000 per year (data based largely on the use of lead shot) with a crippling loss of 247,000 or 14.1 percent of the bag (compiled from Carney et al. 1976, 1978, 1979, 1980, 1981, 1982, 1983, 1984; Schroeder et al. 1975; and Sorensen et al. 1977). Of the total bag, about 930,000 geese are the size of interior Canadas and about 823,000 are smaller.

None of the tests reported here reveals how steel shot performs in the hands of expert hunters who know they are shooting steel and alter their gunning habits accordingly. If such tests were made, we expect that steel would perform significantly better in comparison with lead than it has in the "blind" tests reported here.

Table 9 - Mean number of waterfowl crippled (knocked down but not retrieved) per 100 birds retrieved in the United States before, during, and after the implementation of nontoxic (steel) shot for waterfowl hunting. Data from U.S. fish & Wildlife Service, Office of Migratory Bird Management, Administrative Reports, 1973-1985.

Species
Before (1971-1975)
During (1976-1978)
After (1979-1984)
Ducks
21.6
20.0
19.5
Coots
29.0
28.2
27.1
Geese
14.6
14.9
14.0
All Species
21.4
19.9
19.1

In the United States (1) average annual crippling losses for ducks, coots, geese, and all waterfowl species combined were lower after steel shot implementation (1979-1984) than before implementation (1971-1975); (2) the lowest crippling losses occurred in recent years (1980-1984) when both steel shot and lead shot were used; (3) the highest crippling losses took place in the earlier years (1971-1974) when only lead shot was used; (4) crippling losses have not increased with the increase in use of steel shot in recent years; and (5) the decrease in crippling losses is a long-term trend that began before the implementation of steel shot (Table 9, Figs. 7, 8).

GIF- Crippling rates of waterfowl(pic)
Figure 7 - Crippling rates of waterfowl (ducks, geese, and coots) in the United States, hunting seasons 1971-1984. Data from U.S. Fish and Wildlife Service, Office of Migratory Bird Management, Administrative Reports, 1973-1985.

Because of the long-term downward trend in crippling losses, a simple cause-and-effect relationship cannot be claimed between steel shot and the reduction in crippling losses in recent years. However, the data clearly demonstrate that the use of steel shot has not resulted in an increase in crippling losses in the national waterfowl population. If an effect is present, it is positive - that is, steel shot contributed to a reduction in crippling losses.

GIF- Correlation between crippled waterfowl and year(pic)
Figure 8 - Linear correlation between crippling rates of waterfowl, (ducks, geese, and coots) in the United States and year, hunting seasons 1971-1984. Data from U.S. Fish and Wildlife Service, Office of Migratory Bird Management, Administrative Reports, 1973-1985.

Effect of range
Early shooting experiments with soft steel and lead loads indicated that steel shot was deficient in killing power at ranges of 45.7 m (50 yards) and greater (Bellrose 1959: Table 29; Andrews and Longcore 1969: Fig. 1). More recent field tests with lead and improved steel shot, however, show little difference in killing power between the two loads at long ranges. Anderson and Sanderson (1979: Table 5) found steel shot as effective or better than lead for killing interior Canada geese at ranges >45.7 m (50 yards). Hunters shooting small-to-midsize geese at Tule Lake, California, crippled fewer geese at ranges >45.7 m (50 yards) with steel loads than with lead (Smith and Roster 1979:7). Mikula et al. (1977: Table 4) reported that at ranges >42.1 m (46 yards), hunters failed to retrieve 23 percent of the ducks hit with steel and 32 percent of those hit with lead. Humburg et al. (1982: 124) concluded that bagging, crippling, and missing rates for ducks were similar for steel and lead loads at ranges of >36.6 m (40 yards). Although Hebert et al. (1984:394) found differences in lead and steel shot loads, distance was not a factor in the comparative effectiveness of the two loads for shooting ducks when all distances were combined. Steel loads, however, produced more cripples per shot and per blind-day than lead at <32 m (35 yards) but fewer cripples per shot and per blind-day than lead at >32 m (35 yards).

Gun damage
Almost half the hunters contacted in an Ohio opinion survey taken in 1978 believed that steel shot would damage their guns; 40 percent thought that steel shot would expand the choke and 36 percent thought it would scour the barrel (Smith and Townsend 1981:6). Although the likelihood of excessive gun barrel damage was disproved long ago, the notion lingers. Nearly a decade ago, the three major arms and ammunition companies stated that steel shot causes no significant reduction in the life of most modern full-choke shotguns (U.S. Fish and Wildlife Service 1976). Roster (1978a:6) received no reports or claims of barrel damage after 18,000 rounds of steel shot had been fired. The plastic shot cups prevent steel shot from eroding the barrel. Some choke expansion may occur in full- choked, thinwalled, soft steel shotguns, some Brownings of early vintage, and shotguns with sharp-angled or swadged full choke (Roster 1978a). Magnum lead loads also cause chokes to expand. When there is a minor choke expansion in modern guns, it is largely cosmetic. We find no evidence that steel loads adversely affect modern gun barrels, and barrel damage, therefore, is not a valid reason for refusing to use steel shot.

Cost of shells
The spread in price between steel and lead shot is a deterrent to the use of steel by many hunters (National Wildlife Federation 1985b),but it is a reason more often cited in private than in public. The difference in cost seems to be not so much in the manufacturing of shot as in its retail markup.

One manufacturer's suggested retail prices for selected lead and steel shotgun shells are shown in Table 10 along with percentage comparisons of the costs of loads and shot sizes that are roughly equivalent. Three-inch 20-gauge lead and steel loads are priced essentially the same, but steel 2 3/4-inch 20gauge shells are 27.2 percent more expensive than their lead counterpart. Twelve-gauge steel loads are priced from 7.3 to 25.2 percent higher than approximately equivalent lead loads. Steel loads for 10-gauge shells are listed at 9.3 percent less than comparable lead loads. In practice, however, prices at stores may show larger differences because dealers commonly mark down lead loads and seldom reduce the price of steel loads. Some shooters reload for economy (although some derive pleasure from the mere act of reloading), and components for reloading steel shot are now readily available from at least one reliable source.

Shells, however, make up a minor part of the overall expense of waterfowl hunting. The average duck hunter kills six ducks with 36 shots each year (U.S. Fish and Wildlife Service 1976). At the price differentials noted above, the average duck hunter would spend about $4.50 more on steel than on lead shot shells per hunting season. If a 10- gauge gun were used, a saving of $4.86 would accrue. Since the mid-1930s, waterfowl hunters have responsibly supported funding for wetlands through federal and state duck stamp programs and through contributions to Ducks Unlimited. We conclude, therefore, that the slightly higher cost of steel loads should not be a deterrent to their use, particularly in view of the dwindling populations of ducks and the keen interest of waterfowlers in perpetuating their sport. Furthermore, as the production of steel shot shells increases, costs and consequently prices should decline.

Ballistics
Lead and steel loads differ ballistically. Surprising to many ballisticians, however, steel shot has been found to possess a quality of form retention that makes for a better pattern and a shorter shot string than soft lead. Brister (1976:296,300) pointed out that lead shot pellets become more deformed from impact among the pellets as they pass down the gun barrel than do steel pellets. Steel, which is harder than regular lead shot, resists deformation from pellet impact and, therefore, leaves the barrel in a more nearly spherical form. In addition, steel pellets are more nearly round and are more uniform than lead pellets before they are fired. Because of the larger proportion of steel pellets that remain in spherical form, the steel charge is more compact and has fewer empty spaces and "flyers" in its pattern than is the case for the softer lead shot.

To overcome the deficiency of soft lead, ammunition manufacturers have increased the antimony content and reduced shot-column interstices by the addition of a filler, which buffers the collisions between pellets during their passage through the gun barrel. Buffered lead shot loads are comparable in patterning to steel loads, but in most cases cost more than comparable steel loads (Table 10).

Steel is lighter than lead, but the consequent downrange energy loss can be compensated for by using a steel pellet one or two sizes larger than that used in lead and by increasing muzzle velocity. Because of the greater velocity and the greater retention of form, however, many hunters have learned that steel shot in the same sizes as their favorite lead loads perform satisfactorily.

More steel than lead pellets occur in a given weight. Roster (1978a) found similar numbers of shot pellets in the following paired charges: 1 1/8 oz steel- 1 l/2oz lead, 1 1/4 oz steel-1 3/4 oz lead, 1 3/8 oz steel-1 7/8 oz lead, 1 1/2 oz steel-2 1/8 oz lead, and 1 5/8 oz steel-2 1/4 oz lead.

Evidence suggests that because of the tighter pattern of both steel and buffered lead loads, the ability to aim in relation to choke may well have a bearing on bag/cripple results. This suggestion may be supported by the results of shooting tests at the Schell-Osage Wildlife Management Area, Missouri, where No. 4 lead performed better than No. 4 buffered lead (Table 8). Both the shorter shot string and the tighter pattern of steel contribute to more hits on a target or to a "clean" miss. These factors may explain the generally superior performance of steel shot over lead for hunting Canada geese. Because of the tighter patterns of steel and buffered lead loads, a modified or improved cylinder choke is recommended rather than a full choke.


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