68 



Birds — Our Ln'ing Rf.sourct's 



The U.S. Department of the Interior has 

 imesligated the deaths of more than 

 4,300 bald and golden eagle.s (Haliaeetus 

 leucocephalus and Aqiiila chrysaetos) since 

 the early 1960"s as part of an ongoing effoit 

 to monitor causes of wildlife mortality. The 

 availability of dead eagles for study depends 

 on finding carcasses in fair to good condition 

 and transporting them to the laboratory. 

 Such opportunistic collection and the fact 

 that recent technological advances have 

 enhanced our diagnostic capabilities, partic- 

 ularly for certain toxins, mean that results 

 reported here do not necessarily reflect actu- 

 al proportional causes of death for all eagles 

 in the United States throughout the 30-year 

 period. This type of sampling does, however, 

 identify major or frequent causes of death. 

 Most diagnosed deaths of eagles in our 



30- 



I Bald eagles 

 Golden eagles 



Accidental Gunshot Electrocution Poisoning 

 trauma 



Fig. 1. Causes of mortality of bald and golden 

 eagles over the past 30 years. 



Causes of Eagle Deaths 



J. Christian Franson 



Lou Sileo 



Nancy J. Thomas 



National Biological Service 



study resulted from accidental trauma, gun- 

 shot, electrocution, and poisoning (Fig. 1 i 

 Accidental trauina, such as impacts with 

 vehicles, power lines, or other structures, 

 was the most frequent cause of death in both 

 eagle species (23% of bald and 27% of gold- 

 en). Gunshot killed about 15% of each 

 species. Electrocution was twice as frequent 

 in golden (25%) than in bald eagles (12%), 

 probably because of the preference of gold- 

 en eagles for prairie habitats and their use of 

 utility poles as perches. 



Lead poisoning was diagnosed in 338 

 eagles from 34 states (Fig. 2). Eagles 

 become poisoned by lead after consuming 

 lead shot and, occasionally, bullet fragments 

 present in food items. Agiicultural pesticides 

 accounted for most remaining poisonings; 

 organophosphorus and carbamate com- 

 pounds killed 139 eagles in 25 states (Fig. 

 3). Eagles are exposed to these chemicals in 

 a variety of ways, often by consuming other 

 animals that died of direct poisoning or from 

 baits placed to deliberately kill wildlife. 



Overall, poisonings were more frequent 

 in bald eagles (16%) than golden eagles 

 (6%). The reasons for this are unclear, but 



Necropsy examination of a bald eagle at the 

 National Wildlife Health Center. Madison, 

 Wisconsin. 



may be related to factors that influence sub- 

 mission of carcasses for examination or dif- 

 ferences in species' preferences for agricul- 

 tural, rangeland, and wetland habitats. 



For further information: 



J. Christian Franson 



National Biological Service 



National Wildlife Health Center 



6006 Schroeder Rd. 



Madison, WI 53711 



Fig. 2. Nadonwide distribution of lead-poisoned eagles. 



Fig. 3. Nationwide distribution of eagle poisonings caused by 

 organophosphorus and carbamate pesticides. 



