Research links deer hunting to lead poisoning in eagles

Brad Dokken Beth Siverhus has been a bird rehabilitator since 1996, but she never gave much thought to the possibility that some of her larger patients could be suffering from lead poisoning until earlier this year. That all ...

Poisoned eagle
A bald eagle with lead poisoning breathes through a mask at the Raptor Center in St. Paul in an effort to deliver more oxygen to its lungs. According to Dr. Luis Cruz-Martinez, a veterinarian at the Raptor Center, lead disrupts the red blood cells, making the eagles gasp for air. [Submitted photo]

Brad Dokken

Beth Siverhus has been a bird rehabilitator since 1996, but she never gave much thought to the possibility that some of her larger patients could be suffering from lead poisoning until earlier this year.

That all changed with the news last spring that traces of lead from hunters' bullets were showing up in venison samples tested from food shelves in Minnesota and North Dakota.

For Siverhus, of Warroad, Minn., the news struck a chord for a couple of reasons. She hunts deer, for one thing. And as a wildlife rehabilitator, Siverhus wondered if there could be a reason why most of the bald eagles she received typically came in about the same time as deer season.


She started studying up on the issue, and everything she read, Siverhus said, confirmed the connection. "I felt as if I'd had my eyes closed all these years," she said.

Through an arrangement with Polaris Industries, Siverhus sends all birds of prey on a company airplane from Roseau, Minn., to the Raptor Center at the University of Minnesota in St. Paul, which provides specialized treatment. Last January, Siverhus sent a bald eagle that had been found stumbling in the snow near Baudette, Minn. The eagle died at the Raptor Center.

Then, within a few days in late November and early December, she received a bald eagle rescued from a water-filled ditch near International Falls and a golden eagle found injured along state Highway 220 south of Alvarado, Minn.

The bald eagle died before Siverhus could transfer the bird to the Raptor Center, and its carcass was sent to Colorado. Meanwhile, the golden eagle was euthanized at the Raptor Center last week after tests showed its internal injuries were too severe.

Issue hits home

The dead eagle sent to Colorado showed symptoms of lead poisoning but wasn't tested. In the other two cases, tests confirmed levels of lead in the blood that, if not outright toxic, were high enough to cause other problems.

The golden eagle found near Alvarado had been hit by a car. But the underlying problem, tests showed, was lead poisoning that had weakened the eagle's neurological system to the point where it no longer could fly.

As Siverhus saw for herself, no longer was this a problem occurring somewhere else; it was happening in her backyard.


"With the venison being pulled off food shelves and all of a sudden those articles about raptors with lead poisoning, and then I got three of them," Siverhus said. "It was time to do something."

Siverhus wrote a letter to the editor that appeared in the Dec. 4 edition of the Grand Forks (N.D.) Herald asking hunters to consider alternatives to lead ammunition. That might not sit well with hunters, she concedes. But given what she's seen with lead-poisoned eagles, Siverhus said, it's not an unreasonable request.

"I'm a hunter, and this is not anti-hunting or anti-gun," Siverhus said. "I want hunters to know that. It's 'Let's try to find a solution, a compromise, an alternative to lead ammunition that is cost-effective and works almost the same as

lead.' "

There's a reason, she said, why lead was banned in paint, gas and waterfowl shot. "If hunters could think about a compromise and try not to become angry or defensive until they think this thing through," Siverhus said. "It's going to be a gradual change and hopefully one that won't result in grossly higher cost of ammunition."

Influx of eagles

As they do every year at this time, officials at the Raptor Center have seen an influx of eagles with lead poisoning since mid-November.

According to Dr. Luis Cruz-Martinez, a veterinary resident at the Raptor Center, the facility as of mid-December had received 74 bald eagles this year. Of those eagles, 23 tested positive for lead. There were three positive cases in January, one in February and one in March.


The remaining 18, he said, came in after Nov. 10 -- two days after Minnesota's firearms deer season opener.

"We get these two big peaks in November through January, and then it goes down toward spring and really declines into summer," Cruz-Martinez said. "Then all of a sudden, hunting season -- and all of those birds are lead-

poisoned eagles."

As a graduate student, Cruz-Martinez is expanding and continuing the work of Dr. Patrick Redig, a co-founder of the Raptor Center who has been studying the effects of lead poisoning on eagles since 1974.

Typically, Cruz-Martinez said, the prognosis for eagles with lead poisoning isn't very good.

"We end up releasing only a very small percentage," he said. "A large percentage either die after a couple of days, or we have to euthanize them because of the damages."

Cruz-Martinez said 30 milligrams of lead can kill a bald eagle, and smaller amounts can hamper respiratory and neurological functions. An aspirin, by comparison, weighs 325 milligrams.

Symptoms vary, but often include lime-green-colored feces, an inability to fly and, in advanced stages, labored breathing with gasping sounds.


"They're in good body condition, nutritional health is great, but they eat this toxin, and it really knocks them down," Cruz-Martinez said. "It's quite hard to see this happening. It's something we've been seeing year after year for the last 30-35 years."

Similar trend

Pat Oldham of Bemidji retired as a wildlife rehabilitator in January, but she worked closely with Siverhus and Cruz-Martinez.

Oldham said she handled 119 eagles from 1991, when she started as a rehabilitator in Bemidji, until she retired. About 30 percent of those eagles had lead poisoning.

There were noticeable spikes, she said -- during deer season and again in March, about the time fish houses came off the ice.

"You gut your deer and don't even check it, and that's what eagles eat," said Oldham, who also is a deer hunter. "You could count on November and December being high numbers, and I think if I went back and looked at my paperwork, that would be when I got most of mine."

As a wildlife rehabilitator, Oldham was required to do 12 programs and presentations a year. She figures she spoke to 19,000 people during that time. And in every case, she said, people were surprised to hear that eagles were being poisoned by lead.

"It's very real and much worse than people think," she said. "Every time I spoke and mentioned it, people were shocked. It was a universal response."


Long-term study

Spurred by results from a California study that showed lead from hunters' ammunition was poisoning condors that feasted on gut piles and other remains, the Raptor Center in 1996 began a 12-year study into the impact of lead ammo on eagles in Minnesota.

According to Cruz-Martinez, researchers sampled about 1,100 eagles, and more than 300 had lead poisoning.

Initially, Cruz-Martinez said, researchers had thought the banning of lead shot for waterfowl hunting in 1991 would lower the incidence of poisoning in eagles and other predators at the top of the food chain.

But subsequent studies, such as the condor research in California and Redig's work with bald eagles, found no difference.

"That brought up questions. What other sources of lead are eagles being exposed to?" Cruz-Martinez said. "And the one that really brought our attention was this lead used for ammunition for big game."

In an effort to isolate the source of the lead poisoning, the study looked at the seasonal prevalence and geographical relationship of the cases. Researchers also conducted chemical analyses, comparing the lead found in blood samples with the lead in ammunition fragments.

While the chemical analyses didn't provide definitive proof that the lead was coming from ammunition, all of the birds with lead poisoning also had elevated copper concentrations. That made a stronger correlation, Cruz-Martinez said, because lead bullets also have copper jackets.


The study also found that lead poisoning was more prevalent in northern Minnesota, where deer hunters can use rifles, than in parts of the state where hunting is limited to shotguns with slugs. That has to do with the way rifle bullets fragment, he said, making them easier for raptors to ingest.

Taken together, the study findings offer "nice, strong scientific evidence" that eagles are being poisoned from lead ammunition, Cruz-Martinez said.

"Basically, it was determined after this that more than enough research has been done to prove the lead from ammunition is what is poisoning birds," he said.

Not anti-hunting

Cruz-Martinez, who presented the findings at a May conference in Idaho sponsored by the Peregrine Fund, said it's not an anti-hunting issue, but instead a public health concern.

Eating venison with small fragments of lead won't send anyone to the hospital, he said. But the cumulative effects on children and pregnant women are cause for concern. There are a lot of unknowns.

"Basically, what we're using to hunt animals, to hunt game, is affecting a lot of other wildlife species, and now that lead was found in venison, it's really very striking the potential danger for people.

"All this research in birds has been telling us the problem," he said. "Now that it's gotten into the human [food] chain is when we have our best opportunity to work against this poison to prevent more wildlife mortality and prevent a human disease."

Still, the bald eagle recovery remains one of the great comeback stories of the past half-century. Nearly gone from the lower 48 states by the early 1960s, the number of nesting pairs has grown from about 400 in 1963 to almost 10,000 by 2007, the Department of Natural Resources said, and the bird no longer is on the endangered species list.

In that context, people might ask what the big deal is about a few birds that die from lead poisoning after dining on a gut pile.

"That's one of the things we get a lot: Why bother if a few eagles are dying?" Cruz-Martinez said. "First of all, it's an ethical issue. If you can use another ammo type that will prevent this, why don't you do it? And we really don't know the long-term effects of lead on these eagle populations."

Cruz-Martinez said the Raptor Center has applied for a grant to embark on what he calls an "interdisciplinary approach" to the lead issue. The project, he said, will look at the social and cultural aspects of hunting, the willingness of hunters to switch to nontoxic ammunition and a campaign to educate the public about the potential dangers of lead to humans, animals and the environment.

"Our main goal is to have voluntary switching to nontoxic," Cruz-Martinez said. "We really want to work with hunters, let them know what is happening to wildlife, to people, let them know what is happening right now."

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