Different susceptibilities to white phosphorus poisoning among five species of ducks

Abstract

Three species of ducks, mallard (Anas platyrhynchos), northern pintail (Anas acuta), and green-winged teal (Anas crecca), that frequent an estuarine salt marsh in Alaska during migration die in large numbers from ingesting particles of white phosphorus. Two other common species, northern shoveler (Anas clypeata) and American wigeon (Anas americana), are rarely found dead. Selectivity indices show that this difference in mortality is not due to different numbers of each species being present. We investigated three hypotheses for the difference in susceptibility to this poison. First, we found that wigeons had more total grit in their gizzards than the susceptible species and shovelers had a high proportion of particles >1 mm compared to other species. Thus, ingestion of particles of white phosphorus as grit cannot explain the differences in susceptibility. Second, feeding behavior could not completely account for the lack of susceptibility in shovelers. Shovelers often forage with their neck or more in the water and often have their bills in the sediments. Wigeon, however, frequently forage with just their bill in the water and rarely penetrate the sediments. This feeding behavior, coupled with a diet consisting mainly of plants, may limit exposure of wigeon. Third, shovelers have wide upper bills, with lamellae consisting of long thin filaments extending from the upper bill inward toward the lower bill. These lamellae may allow white phosphorus particles to be flushed out during feeding. Thus, if physiological tolerance to white phosphorus is similar among these species, the difference in susceptibility appears to be due to differences in feeding behavior and bill morphology.