Research – Eagles and Lead
SOAR began gathering data in 2004 on the admissions of bald eagles to wildlife rehabilitators in Iowa. Eagle data includes: date of admission, cause for admission, gender, adult/juvenile, county found, lead levels from blood sample or liver or bone biopsy, and if euthanized, died, or released.
SOAR has also looked for the source of the lead, as able, through x-ray, CT scan, or fluoroscope image of eagles and other raptors that show symptoms of lead, and deer carcass and packaged venison. SOAR has documented eagles and other scavengers feeding on carcasses.
Signs of toxic lead levels in raptors include ataxia (muscle weakness and an inability to control voluntary muscle movement due to central nervous system being affected), lime-green feces, vomiting, seizures, partial of full paralysis of the wings and legs, impaired vision, and death.
A Sad Full Circle
In 2006, this bird came in from Mills County with a band. She was banded as nestling in Shell, Missouri in 1986! She had a fractured humerus — which Ross Dirks, DVM, at Dickinson County Animal Clinic, Spirit Lake pinned. The wing healed nicely, she spent eight weeks in intensive care. After one month in the 100 foot flight she is ready to go. Kathy Hodges releases her on our farm in honor/memory of her son Drew, who had just died from cancer.
In March 2009 a call from the warden in Mills County, has a dead eagle with a band — yes our baby. Liver biopsy showed lead poisoning as cause of death. She was 23 years old and in perfect feather.
What did she likely eat in February or March 2009? Yep, she probably had been feeding on a lead-shot deer gut pile or a deer that had been shot with a lead slug and not found by the hunter.
How could this death have been prevented? If the hunter had used a non-lead slug to harvest that deer there would have been no lead shrapnel left behind to impact a non-target species.
How do we test for lead?
Testing for lead can be done two ways; blood samples and liver or bone samples. While the bird is still alive, blood samples can be taken and analyzed. Liver and bone biopsies are completed only after the bird dies. Test results can be expressed in parts-per-million (ppm) or micrograms per deciliter (µg/dL). For reference, 0.1 ppm = 10 µg/dL.
Blood lead level test results and what they mean:
- Under 0.2 ppm (<20 µg/dL) is background and is considered normal.
- Between 0.2-0.6 ppm (20-60 µg/dL) is considered a toxic lead level and indicates exposure to lead, but may not be lethal by itself and may or may not require treatment, based on symptoms.
- 0.6 ppm and above (>60 µg/dL) is considered a lethal lead level and most likely will chelate
Liver biopsy results and what they mean:
- Less than 2.0 ppm is background and is considered normal.
- Between 2.0 ppm and 6 ppm is considered toxic exposure to lead.
- 6 ppm and greater is considered a fatal lead level.
Exposure to lead can cause the animal to be impaired and not be able to catch prey, avoid collisions, etc. so exposure levels are still potentially lethal indirectly.
Lead availability study
SOAR, in partnership with Whiterock Conservancy, conducted a field survey during the 2008 winter shotgun deer season to document the incidence, abundance, and distribution of available lead fragments in white-tailed deer carcasses harvested with lead slugs. Fourteen lead-slug-shot white-tailed deer carcasses and associated gutpiles were borrowed from cooperating hunters for x-ray. SOAR’s Lead Availability Study (437 KB PDF)
Cumulative bald eagle data 2004-2014
Data compiled by SOAR – Saving Our Avian Resources from all wildlife rehabilitators in Iowa (Black Hawk Wildlife Rehabilitation Project, Macbride Raptor Project, Orphaned & Injured Wildlife, SOAR – Saving Our Avian Resources, and Wildlife Care Clinic) that admit eagles. We now have 11 years of data with 322 eagle admits.
Beginning in 2004, wildlife rehabilitators admitting bald eagles began testing for lead levels in blood (alive) or in bone (if dead) and taking x-rays to look for ingested lead. An abnormal lead level is above 0.2 ppm as a blood lead level or above 2.0 ppm as a liver lead level.
In 2014, 42 eagles were admitted across the state. Of those 42, 38 were tested for lead levels and 16 of those tested showed abnormal lead levels.
In the 11 years of data only 49 of the 322 eagles admitted DID NOT have a lead level checked. 136 of the 273 eagles tested (or 50%) had an elevated lead level. 136 of the 322 eagles admitted (or 42%) had an elevated lead level.
X-rays of eagles, deer, ground venison
Bald eagles and other large raptors are not only predators, but they also are opportunistic scavengers. What does this mean? Simply, an opportunistic scavenger is not likely to ignore a large carcass laying in a field or alongside the road. Field observations of eagles confirm their behavior of seeking out and feeding from large carcasses for several days at a time.
Yes, this is an eagle feeding station — SOAR salvaged roadkill deer (with the necessary permit from an Iowa DNR conservation officer to pick up) and carp and placed in a field in Carroll County, along with a motion-activated trail camera. The dates on the photos are correct, but the time stamp is wrong. SOAR is, of course, very careful to examine carcasses to make sure there is no chance of lead. Please do not use butcher scraps from lead-shot animals or leave animals shot with any type of lead ammunition out for predators or scavengers to eat.
The Peregrine Fund hosted this conference in Boise, Idaho with the goal of the conference to promote a better understanding of spent lead ammunition as a source of lead exposure and to reduce its effect on wildlife and humans.
Bald Eagle Lead Poisoning in Winter; Abstract presented at The Peregrine Fund “Spent Lead Ammunition” conference (689 KB PDF)
Iowa Lead Advisory Group Action Plan (272 KB PDF)
SOAR received an Iowa Resource Enhancement and Protection – Conservation Education Program (REAP-CEP) grant to form a Lead in the Environment Advisory Group. This Advisory Group would bring together the stakeholders involved in the issue of lead in ammunition and tackle. Through meetings, focus groups, and discussion a plan of action to address this issue was formulated.