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Redig, P.T., G.E., S. Schwartz, and E. Lawler. 1983. An investigation into the effects of lead poisoning on bald eagles and other raptors. Final report submitted to the Minnesota Department of Natural Resources. Unpaged.
Summary:
Lead poisoning occurring as a result of the ingestion of lead shotgun pellets embedded in the flesh of prey species as well as the ingestion of contaminated flesh of animal that have died from lead poisoning has gain recognition as a discrete mortality causing factor among Bald Eagles (Haeliaeetus leucocephalus wintering in the vicinity of large waterfowl concentrations and has been shown to affect other species of raptors and scavenging birds. The following objectives were addressed in this study: 1) refinement of immune functions assays (lymphocyte blastogenesis and antibody response to sheep red blood cells) for use in raptors 2) experimental evaluation of the effects of chronic sub-lethal, sub-clinical exposure to lead acetate on hematological, serum chemical, and immunological function in red-tailed hawks (Buteo jamaicensis) 3) determination in wild bald eagles admitted to the raptor research and rehabilitation program at the University of Minnesota of the plasma concentrations of lead, ZN-bound protoporphyrin, Porphobilinogen Synthase enzyme activity, Hemoglobin concentration, Hematological, and serum chemical parameters in order to assess the morbidity and physiological significance of elevated lead plasma concentrations in these birds.
A conclusion may be drawn that suggests widespread lead poisoning in the eagle population reduces the foraging efficiency of the birds and renders them more susceptible to serious injury causing modes of food acquisition such as scavenging trap baits and dead carcasses from along roads. Specific conclusions from this study include: 1) Significantly elevated plasma lead residues are present in the majority of eagles involved in serious injuries 2) Lead residues above 1.0 PPM do occur in eagle population and are associated with clinical lead poisoning. Many of these affected birds can be expected to die or be partially crippled, even with treatment, due to permanent damage to organ and enzyme systems 3) Where lead residues are moderately elevated, PBG-S is significantly decreased and ZPP is significantly increased, such an affected bird has had long term repeated exposure to lead 4) Where lead residues are approaching 1.0 PPM or greater, the exposure to lead has probably been acute unless PBG-S and ZPP are significantly altered 5) significant disparity in the values for lead concentration exist between reputable laboratories, hence, other parameters should also be measured to accurately assess the lead status of individual birds 6) The immune system is more refractory to the effects of lead than are the hemoglobin synthesizing mechanisms 7) Physiological recovery from even very low exposure to lead requires 4-5 weeks and lags far behind the outward appearances of clinical recovery.