We start off with light heart, but as we near the marsh, we stop abruptly in shock and horror. The shoreline, where only last evening we saw thousands of sleek, apparently healthy birds, is now littered with their bodies. Most of them are ducks, but here and there we see a Canada goose, a gull, an avocet, a black-necked stilt, a pelican.....

This is the way Jensen and Williams (1964) described an outbreak of avian botulism in a western marsh. It illustrates, more vividly than dry facts and body counts, the impact a disease can have on a population of waterfowl.

When we think about waterfowl diseases, we probably think first of botulism and then of lead poisoning, the result of birds swallowing spent lead shot. In fact, these are the only two diseases discussed by Kortright (1942) and Day (1949) in major books on North American waterfowl, attesting to both their importance and our years of experience with them. Botulism was probably an old problem in 1910, but the catastrophic loss that summer of millions of aquatic birds near the Great Salt Lake and in California marked the beginning of real concern about its impact on waterfowl populations (Jensen and Williams, 1964). Concern about lead poisoning of waterfowl began a few years later following the investigations of Wetmore (1919).

Today, more than 50 years after these early reports, botulism and lead poisoning are still major disease problems of North American waterfowl, but they are no longer the only ones. After years of study, we have learned much about how these two diseases occur and about their prevention and control. But now there are new pathogens and new toxic compounds that can afflict waterfowl populations. So rather than redescribe the established disease problems of the past and present, I will concentrate on some of these new waterfowl disease problems of the present and future.