DIFFERENT SUSCEPTIBILITIES TO WHITE PHOSPHORUS POISONING AMONG 5 SPECIES OF DUCKS

Three species of ducks, mallard (Anas platyrhynchos), northern pintail (Anas acuta), and green-winged teal (Anas crecca), that frequent an e stuarine salt marsh in Alaska during migration die in large numbers fr om 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 pr esent. We investigated three hypotheses for the difference in suscepti bility to this poison. First, we found that wigeons had more total gri t in their gizzards than the susceptible species and shovelers had a h igh proportion of particles >1 mm compared to other species. Thus, ing estion of particles of white phosphorus as grit cannot explain the dif ferences in susceptibility. Second, feeding behavior could not complet ely account for the lack of susceptibility in shovelers. Shovelers oft en forage with their neck or more in the water and often have their bi lls in the sediments. Wigeon, however, frequently forage with just the ir bill in the water and rarely penetrate the sediments. This feeding behavior, coupled with a diet consisting mainly of plants, may limit e xposure of wigeon. Third, shovelers have wide upper bills, with lamell ae consisting of long thin filaments extending from the upper bill inw ard toward the lower bill. These lamellae map allow white phosphorus p articles to he hushed out during feeding. Thus, if physiological toler ance to white phosphorus is similar among these species, the differenc e in susceptibility appears to be due to differences in feeding behavi or and bill morphology.