ABSTRACT.—The ingestion of spent lead shot was known to cause mortality in wild waterfowl in the US a
century before the implementation of nontoxic shot regulations began in 1972. The biological foundation
for this transition was strongly supported by both field observations and structured scientific investigations.
Despite the overwhelming evidence, various societal factors forestalled the full transition to nontoxic shot
for waterfowl hunting until 1991. Now, nearly 20 years later, these same factors weigh heavily in current