A bit more about lead poisoning…

x-ray of eagle pelletThe bald eagle admitted on 13 December 2011 that had been caught in a leg-hold trap also had elevated blood lead levels (BLL) of 9.6 µg/dL. She coughed up a pellet (accumulated undigested material, in the case of eagles primarily hair) shortly after initial exam at SOAR. This pellet was x-rayed for lead fragments. The bright white flecks are lead fragments that were not dissolved and absorbed into her blood stream.

The leg-hold traps were set near a deer carcass. Had she not been caught in the trap and found, it is likely she would’ve continued to eat off this deer carcass and ingest more lead.

2EaglesOnCarcassA 1997 University of Minnesota Raptor Center retrospective study concluded that spent lead ammunition is an important source of lead exposure for bald eagles. TRC also undertook a subsequent retrospective study to test the hypothesis that lead fragments in carcasses and gutpiles of white-tailed deer represents an important source of lead exposure lead in bald eagles. Read this research paper published in Spring 2012. (461 kb PDF)

Since 2004, SOAR has been compiling statewide eagle data that now includes over 180 eagles. All of these eagles had either a BLL taken or the lead level was determined post-mortem via liver biopsy. Over half of these eagles had abnormal lead levels in blood, liver, or bone. This is a much higher percentage than the random types of injuries, seen in other species.

In a 2008 paper presented at the Peregrine Fund’s Spent Ammunition Conference, SOAR Executive Director Kay Neumann noted, “…more random events seem to occur at a much lower percentage of the total number of eagles admitted. Gunshot wounds, for example, were recorded in ten of the 82 [those in the database up to the submission of the paper] eagles in this database (12.2%). The data does not indicate that the increasing number of bald eagles being admitted by Iowa wildlife rehabilitators is simply a function of the increasing numbers of eagles in wild populations. If this were the case, it would be expected that a variety of causes would be seen for admittance (miscellaneous trauma, fractures, starvation, disease, etc.), at percentages relative to that seen for gunshot wounds. This has been the case for other species.”

Cooper's hawkFor instance, the Cooper’s hawk (see photo at right) population has rebounded from DDT exposure and have also increased numbers by discovering a new niche — Cooper’s hawks are now nesting in town. As would be expected, a higher population means that more birds will be seen by rehabilitators. In the last 4-5 years, there has been an increase in Cooper’s hawks being admitted to rehabilitators across the country with a random assortment of injuries, not just one.

As reported in the 14 December 2011 issue of the North Iowa Times, “Dr. Julie Ponder of the Raptor Center at the University of Minnesota sees about 100 eagles per year. The Raptor Center is one of the premiere raptor treatment and research facilities in the country. All receive blood testing for lead, as well as an x-ray. She said that 95 percent of the birds show some lead exposure, and 25-30 percent have lead poisoning. That’s a pretty significant number.”

Lead poisoning affects eagles more than other raptors. Thousands of bald eagles winter in Iowa — estimates of up to one-fifth of the lower 48 states’ eagle population — congregate near open water along the big rivers and reservoirs in the state. Other scavengers like turkey vultures have migrated south. Hawks tend to hunt more than scavenge and an eagle will chase off hawks feeding on a carcass.

Iowa has deer hunting seasons for hunters from September (for youth hunts) through January (extended doe season). The extended hunting seasons mean an increased opportunity for deer carcasses to be available at a time when thousands of eagles are in Iowa.

“This is a problem that we can solve,” Dr. Laura Johnson, a veterinarian and a licensed wildlife rehabilitator at Tender Care Animal Hospital in Prairie du Chien, Wisconsin, said in an interview with the North Iowa Times. “We want people to know that they can change the kind of ammunition they use,” she added.

For information about non-toxic ammunition, please visit the Hunt and Fish Lead-Free page and the Non-toxic Alternatives page.