Lead Poisoning Problem for Wildlife
as well as for People

by Carol Lee

March 9, 2003
Lubbock Avalanche-Journal

Lead is a naturally occurring metal that is toxic to humans as well as to animals.

Lead exposure in humans can result in irreversible brain and kidney damage, muscle weakness, reproductive dysfunction, gastrointestinal disorders, headache, anemia and others.  Fetuses and young children are most at risk.

Not only does lead cause illness and debilitation in humans, but it also affects many wild animals.

Since ducks regularly search for food on the bottoms of lakes and streams, they ingest gravel that is used in the gizzard to help grind up food for digestion.  Not being able to distinguish between a piece of gravel or a lead pellet, they are vulnerable to eating shot that settles on the bottom of lakes.

According to Toby McBride, a doctoral student at Texas Tech's Institute for Environmental and Human Health, feeders such as "swans, geese, cranes and some duck species use aquatic plants as a primary food source, and they eat large amounts of sediment in the process.  These animals are then exposed to lead shot remaining in lake and marshland sediment.

"Concerns over lead in wildlife were not expressed until the 1950s, when great numbers of waterfowl deaths were recognized as the result of lead use in firearm munitions and fishing sinkers."

He said research shows that more than 100,000 lead pellets per acre could accumulate by the end of the hunting season, and concluded that "4 percent of the waterfowl population was dying annually due to ingesting lead shot."

Lead poisoning also can affect shorebirds, pheasants, doves and quail.  It also kills bald and golden eagles.

Here on the high plains, eagles coexist with waterfowl and follow the flocks of geese and ducks, in turn making them susceptible to ingesting the pellets when they eat waterfowl.

In these and other predatory birds, poisoning results when the lead shot embedded in the flesh of the prey is eaten.  Pellets are ground down during digestion and the lead is then absorbed into the body as lead salt that disturbs the digestive and nervous systems.

In birds, symptoms of lead poisoning include neurological and gastrointestinal problems; limb paralysis, staggering, and difficulty walking on land; and wings can be mal-positioned or drag on the ground.  Symptoms may also include vocal changes, such as a high-pitched honk, swelling in the face or esophagus and bright green feces.

An affected bird is reluctant to fly, and unable to sustain flight.  Anemia, muscle wasting and overall emaciation ensue.

Lead poisoning also produces a consistent and chronic weight loss.  Often a bird dies after ingesting only one or two pellets, losing up to 50 percent of its body weight.  Occasionally, a bird will ingest many lead pellets, resulting in acute lead poisoning, and it dies quickly without significant weight loss.

The large mute swan sighted around Lubbock for many months was brought to the South Plains Wildlife Rehabilitation Center last fall.  It was too sick from lead poisoning to avoid capture and died at Animal Medical Center.  The cause was from ingesting split shot fishing sinkers from local playa lakes.

Melissa Baird, Texas Tech undergraduate researcher and an intern at the center, followed up on this case and did studies on the occurrence of lead poisoning to raptors and waterfowl.  She is analyzing lead levels in liver and kidney samples from all deceased raptors and waterfowl collected at the center.  Early findings documented four birds (10 percent of those collected) with lethal lead levels in their tissues.

Baird and McBride are part of a nationwide investigation into secondary lead ingestion risks for eagles, hawks and falcons.  This is in cooperation with Hawk Watch International and 30 raptor research and rehabilitation centers across the country.

Blood samples for lead analyses were collected from all raptors admitted during the winter months of 2002-2003.  McBride said these analyses would allow researchers to examine nationwide lead-concentration trends and identify regions and species of concern.

So what's being done?

The U.S. Fish and Wildlife Service's 1991 nationwide ban on the use of lead shot for waterfowl hunting has had significant success preventing the premature deaths of millions of waterfowl from lead poisoning.

Nontoxic shot is now the standard.  Approved shot types include steel, Bismuth-tin, Tungsten-iron, and others.

Finally, it's important to educate fishermen on the dangers to waterfowl when they are careless and leave lead sinkers and other tackle around our lake perimeters.

###

Carol Lee is the executive director of the South Plains Wildlife Rehabilitation Center, Inc.  She can be reached at spwrc(at)cox.net.

Updated 19 July 2006 .