SITE-SPECIFIC LEAD-EXPOSURE FROM LEAD PELLET INGESTION IN SENTINEL MALLARDS

We monitored lead poisoning from the ingestion of spent lead pellets i n sentinel mallards (Anas platyhrynchos) at the Sacramento National Wi ldlife Refuge (SNWR), Willows, California for 4 years (1986-89) after the conversion to steel shot for waterfowl hunting on refuges in 1986. Sentinel mallards were held in 1.6-ha enclosures in 1 hunted (P8) and 2 non-hunted (T19 and TF) wetlands. We compared site-specific rates o f lead exposure, as determined by periodic measurement of blood lead c oncentrations, and lead poisoning mortality between wetlands with diff erent lead pellet densities, between seasons, and between male and fem ale sentinels. In 1966, the estimated 2-week rate of lead exposure was significantly higher (P < 0.005) in P8 (43.8%), the wetland with the highest density of spent lead pellets (>2,000,000 pellets/ha), than in those with lower densities of lead pellets, T19 (18.1%; 173,200 pelle ts/ha) and TF (0.9%; 15,750 pellets/ha). The probability of mortality from lead poisoning was also significantly higher (P < 0.01) in sentin el mallards enclosed in P8 (0.25) than T19 (0) and TF (0) in 1966 and remained significantly higher (P < 0.001) during the 4-year study. Bot h lead exposure and the probability of lead poisoning mortality in P8 were significantly higher (P < 0.001) in the fall of 1986 (43.8%; 0.25 ), before hunting season, than in the spring of 1987 (21.6%; 0.04), af ter hunting season. We found no significant differences in the rates o f lead exposure or lead poisoning mortality between male and female se ntinel mallards. The results of this study demonstrate that in some lo cations, lead exposure and lead poisoning in waterfowl will continue t o occur despite the conversion to steel shot for waterfowl hunting.