Jl. Moore et al., SHOT PREVALENCES AND DIETS OF DIVING DUCKS 5 YEARS AFTER BAN ON USE OF LEAD SHOTSHELLS AT CATAHOULA LAKE, LOUISIANA, The Journal of wildlife management, 62(2), 1998, pp. 564-569
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.