SHOT PREVALENCES AND DIETS OF DIVING DUCKS 5 YEARS AFTER BAN ON USE OF LEAD SHOTSHELLS AT CATAHOULA LAKE, LOUISIANA

Catahoula Lake, central Louisiana, is a RAMSAR Convention Wetland of I nternational Importance and among the most important wintering and sta ging areas for waterfowl in North America. To evaluate exposure rates in Catahoula Lake waterfowl 5 years after a ban on use of lead shot, w e determined the prevalence of ingested shot and diets of canvasbacks (Aythya valisineria) and lesser scaup (A. affinis) salvaged from comme rcial fishing nets in winter 1992-93. Plant material composed >77% of the midwinter diet of canvasbacks. Consumption of belowground plant ma terial (e.g., chufa flatsedge [Cyperus esculentus] and arrowhead [Sagi ttaria spp.] tubers) exceeded 47% in 1992-93, but was lower than in 19 87-88. Male lesser scaup fed almost exclusively on plant material, esp ecially bearded sprangletop (Leptochloa fascicularis) and millet (Echi nochloa spp.). Prevalence of ingested lead or steel shot was similar i n canvasbacks (38%) and lesser scaup (34%) in spite of differences in foraging behavior, suggesting that ducks actively selected shot as sit . Shot (lead or steel) prevalence in diving ducks at Catahoula Lake wa s similar in winters 1987-88 and 1992-93, but the proportion of birds with lead in their gizzards was greatly reduced in 1992-93 (6%) compar ed to 1987-88 (27%). Because ingestion of lead shot deposited in wetla nds prior to steel shot regulations remains a problem at some sites, w e suggest that provision of nontoxic grit may serve to reduce lend sho t prevalence in waterfowl at contaminated sites.