1. Anderson, W.L. and Havera, S.P. (1985) Blood lead, protoporphyrin, and ingested shot for detecting lead poisoning in waterfowl. Wildlife Soc. Bull. 13, 26?31.
2. Anderson, W.L., Havera, S.P. and Montgomery, R.A. (1987) Incidence of ingested shot in waterfowl in the Mississippi Flyway, 1977?1979. Wildlife Soc. Bull. 15, 181?8.
3. Bart, J. and Robson, D.S. (1982) Estimating survivorship when the subjects are visited periodically. Ecology 63, 1078?90.
4. Bellrose, F.C. (1959) Lead poisoning as a mortality factor in waterfowl populations. Illinois Nat. Hist. Surv. Bull. 27, 235?88.
5. Bellrose, F.C. (1976) Ducks, Geese and Swans of North America, 2nd Edn. Harrisburg, PA: Stackpole Books.