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, circumstance of 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 (antemortem), blood samples can be taken and analyzed. Liver and bone biopsies are completed only after the bird dies (postmortem). 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 subclinical 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 clinical 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 subclinical exposure to lead.
- 6 ppm and greater is considered a clinical 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.
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. In the 11 years of data we have 322 eagle admits.
The data and what we learned is published in published online in the Journal of Fish and Wildlife Management!
Thanks need to go to many people… Jodeane (at the Macbride Raptor Project then, now at The RARE Group), Terese and Dr Lori and volunteers with Black Hawk Wildlife Rehabilitation Project, Dr Z and staff at the Wildlife Care Clinic, SOAR volunteers for rescuing, transporting, collecting data, treating, and all that goes in to helping sick and injured eagles! Data collection is likely the least favorite activity in all of this… but oh so important! Thanks also to Dr Z, Taylor, and Adam for help with statistics and organization. Without the data, this paper could not have been published.
What did the data tell us about the lead exposure to bald eagles in Iowa?
- The data gathered by wildlife rehabilitators in Iowa on lead exposure in bald eagles are consistent with datasets from many other rehabilitation centers.
- Adult bald eagles had higher lead concentrations than immature or juvenile bald eagles, consistent with data on rehabilitating bald eagles (Cruz-Martinez et al. 2012) and data from bald eagles found dead (Franson and Russell 2014).
- Lead concentrations were highest across all age classes during the autumn (October–January), which coincides with the hunting and trapping seasons in Iowa.
- Wildlife rehabilitators routinely collect blood samples from bald eagles admitted. Prioritizing blood collection for a blood lead analysis in bald eagles can help direct care.
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.
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)
X-rays of eagles, deer, ground venison
This x-ray shows a lead fragment in the eagle, about where the stomach would be. X-ray provided by MacBride Raptor Project.
X-ray of a deer carcass that was shot with lead deer slugs, reveals that the main body of the slug traveled completely through the deer, but lead shrapnel fragments were left in the carcass at the points where the slugs passed through and shattered bone. This shrapnel looks quite similar to the irregular shrapnel pieces found in eagle digestive systems. In this x-ray of a deer’s mid-section, you can see the lead fragments where the slug went through the ribs below the spine and grazed the top of the spine.
This is an x-ray of a pellet that was coughed up by an eagle just after having received fluids at admission. This eagle tested positive for lead poisoning.
Packages of ground venison were x-rayed for lead fragments.
The bright, white fleck in this x-ray of ground venison is lead.
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.