William L. Hohman
Timothy M. Stark
Gary A. Weisbrich
Joseph L. Moore
1998
<p>Catahoula Lake, central Louisiana, is a RAMSAR Convention Wetland of International Importance and among the most important wintering and staging areas for waterfowl in North America. To evaluate exposure rates in Catahoula Lake waterfowl 5 years after a ban on use of lead shot, we determined the prevalence of ingested shot and diets of canvasbacks (<i>Aythya valisineria</i>) and lesser scaup (<i>A. affinis</i>) salvaged from commercial fishing nets in winter 1992-93. Plant material composed >77% of the midwinter diet of canvasbacks. Consumption of belowground plant material (e.g., chufa flatsedge [<i>Cyperus esculentu</i>s] and arrowhead [<i>Sagittaria</i> spp.] tubers) exceeded 47% in 1992-93, but was lower than in 1987-88. Male lesser scaup fed almost exclusively on plant material, especially bearded sprangletop (<i>Leptochloa fascicularis</i>) and millet (<i>Echinochloa</i> spp.). Prevalence of ingested lead or steel shot was similar in canvasbacks (38%) and lesser scaup (34%) in spite of differences in foraging behavior, suggesting that ducks actively selected shot as grit. Shot (lead or steel) prevalence in diving ducks at Catahoula Lake was 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%) compared to 1987-88 (27%). Because ingestion of lead shot deposited in wetlands prior to steel shot regulations remains a problem at some sites, we suggest that provision of nontoxic grit may serve to reduce lead shot prevalence in waterfowl at contaminated sites.</p>
application/pdf
10.2307/3802330
en
Wildlife Society
Shot prevalences and diets of diving ducks five years after ban on use of lead shotshells at Catahoula Lake, Louisiana
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