Renee DiPietro, CVT
Veterinary Information Specialist
Permitted Wildlife Rehabilitator
The Bald Eagle (Haliaeetus leucocephalus) is dying in our wetlands, plains and uplands on a daily basis. The issue is lead in the environment. This heavy metal is highly toxic to birds and is killing our nation’s carnivorous birds, water fowl, and ground dwelling birds at alarming rates.
Lead is a naturally occurring heavy metal that has been used by humans for a variety of applications since approximately 3000 BC. Trace amounts are found occurring naturally in soil, water, and plants. This metal is attractive for its malleability, corrosion resistance, high density and low melting point. Its refinement and production is also significantly less costly than that of many other metals. It has been widely used for plumbing over the centuries. The word “plumber “ is actual derived from this metal’s elemental symbol on the periodic table, Pb. Pb is derived from the latin word Plumbum which when translated is “Liquid Silver”. Lead has been used widely through history for utilitarian and ornamental purposes. During the time of the Roman Empire lead was celebrated as the finest metal in which to cook and to make wine. It was thought that the metal imparted a sweet flavor that improved the quality of gastronomic products. Lead acetate or “Sugar of Lead” was a popular food additive for flavor enhancement. As many as a fifth of ancient roman recipes called for lead as an ingredient.
While much celebrated and utilized for thousands of years, an insidious thread of malady accompanies lead on its journey through time. During the Roman Empire, the population, especially those of aristocratic status were subject to a plethora of unexplained medical ailments ranging from infertility and gout, to psychosis. There are even those that have postulated that the fall of the Roman Empire was largely influenced by this unrecognized toxicity. It is suspected that at the height of this period the average aristocratic Roman consumed between 35-250 mg of lead per day. This is in stark contrast to measurements done in the 1980s that estimate the average American’s daily lead intake as 0.3 mg/day. Lead is also suspected to have killed other notables including Beethoven.
Endemic Chronic Plumbism is now suspected to have negatively impacted several societies throughout human history. Although as early as the Roman Empire, people began to suspect that lead consumption may have been contributing to their ailments, society has continued to utilize this metal for innumerable applications.
In high doses lead causes significant damage to the brain and central nervous system. Lower, more chronic doses can also have ill effects including cognitive dysfunction, renal toxicity, gastrointestinal, cardiovascular and reproductive effects. During the industrial revolution lead surged again as an immense resource for the manufacture of various goods. Since this explosive increase in usage, lead has become a persistent environmental pollutant and hazard to humans and wildlife. By the early 20th century lead exposure was widespread in items such as petrol gasoline and lead based paints used commonly in residential painting applications. Lead can also be found in pigments, dyes, caulks, metal alloys, batteries, and aviation fuels. It was during this time period that lead toxicity became more widely recognized as a threat to human health, especially to children. During the mid to late 1900s regulations were put in place to eliminate lead in commonly used products including gasoline and paint. These restrictions in wealthier countries have greatly reduced human exposure to lead. In poorer countries with less regulation people are still exposed to high levels of lead on a daily basis in household objects, manufacturing debris and environmental contamination from mining and smelting type operations.
How does this all pertain to the Bald Eagle? Birds are very sensitive to lead toxicity. We have seen what it can do to humans. At a blood level of just 1ppm it is lethal to our nation’s wild birds. Most heavily affected are waterfowl and raptors (carnivorous birds). Why? Lead is a commonly used metal from which to fabricate munitions and lead sinkers for fishing. In a one year period in the United States over 69,000 tons of lead is used to produce munitions. In five lakes studied, as much as 320lbs per lake of Pb sinkers from fishing line have been documented. Spent ammunition and fishing tackle are major sources of lead contamination and toxicity for wild birds. There are various exposure scenarios for birds.
In areas of around shooting ranges, birds pick at the soil in an effort to ingest grit as a digestive aid. High concentrations of lead can be found in these soils. Lead is inadvertently and commonly ingested from the environment by waterfowl and from prey/carrion by raptors. Hunting areas are considered to pose a higher risk of lead ingestion than shooting ranges. Fragmented lead from bullets and shot left in dead or dying animals is ingested by carnivorous birds of prey. In wetland areas lead sinker material and lead shot are picked off the bottoms of waterways by feeding waterfowl. After significant numbers of water fowl deaths were associated with lead shot used for waterfowl hunting, the use of lead shot for this purpose was banned in the United States. Even with the longstanding ban of lead shot over waterways this environmental contaminant persists and waterfowl deaths due to lead toxicity are still frequently reported. The Trumpeter Swan is one example of waterfowl commonly killed by lead ingested from the environment. Birds of prey (Eagles, Hawks, Condors, Osprey, Owls, Vultures, Merlins, Falcons) also scavenge and are most commonly exposed by ingesting lead bullet fragments or shot from deer, squirrels, rabbits, and other prey killed in upland hunting where the use of lead munitions is not currently banned. Ground feeding species such as doves, bobwhites, and pheasants are also heavily represented in bird species affected by lead toxicity. Exposure to lead at sub lethal and lethal levels has been documented in upwards of 120 avian species. Quantification is challenging as toxicity is rapid and not all species are monitored with consistent intensity. Ingestion of a particle of lead the size of 1 grain of rice can kill 3-4 adult bald eagles. A bird of prey can easily ingest a toxic dose in just one feeding. In some cases toxic dosing is cumulative. Lead bullets expand and dissipate throughout flesh when they pierce an animal. With x-ray analysis it has been determined that on average 235 fragments of lead are distributed in a 16-20 inch area of flesh from where a bullet hits its animal target. Another study showed that up to 30 % of a bullet gets left behind even when there is an exit wound. One of these fragments can lead to toxicity and death for a bird of prey. One carcass or field dressed gut pile can expose several individual birds to lead toxicity.
When lead is ingested by birds it is exposed to the highly acidic environment of the stomach which causes it to break down quickly and become absorbed from the gastrointestinal tract to the blood stream. Once in the blood stream its toxic effects can be carried throughout the body to wreak havoc on various body systems. Various species have different physiological sensitivities to lead toxicity. California Condors and Bald Eagles are significantly sensitive species. Conversely the Turkey Vulture has been found to have a higher tolerance for lead toxicity. Lead uptake and dispersal in the blood stream and other physiological systems of birds can modify the structure and therefore the function of the kidneys, bones, central nervous system, and blood. One affect lead has in the body is that it can mimic calcium and disturbs systems that depend on its uptake such as the central nervous system. Blood changes such as anemia are also often seen. The cerebellum is often affected and behavior changes result. (Much like the Ancient Romans!) Toxic effects can be acute and quickly lethal or accumulate to chronic toxicity over time with symptoms such as anorexia (lack of appetite), lethargy (lack of energy) and muscle wasting observed. Blindness is another symptom of lead toxicity.
The California Condor is an obligate scavenger that nearly came to extinction in the 1980s. Only nine birds were found to be alive in the wild. These birds were captured and then successfully restored with a captive breeding program designed to rescue them from extinction. Although the cause of their near extinction was a long held mystery it is now speculated that lead toxicity from bullet fragments ingested during their necessary scavenging activities was a major contributor. This species tends to feed socially/communally, increasing the risk that exposure to one carcass or offal deposit could expose several to many birds to lead toxicity. The California Condor is a bird species that does not regurgitate its food after ingestion which leads to higher retention of lead particles compared to those species of birds that do habitually regurgitate. Since the California Condor’s precipitous encounter with extinction, legislation has been passed in California banning the use of lead munitions in Condor critical habitat areas.
Bald Eagles are another species highly sensitive to lead toxicity and the effects of this are seen profoundly in many states. In 2016 the Wildlife Center of Virginia admitted 38 bald eagles. 80 percent of those birds had measurable levels of lead in their blood. In addition to deaths and illness directly caused by lead toxicity, eagles can injure themselves or become more easily injured by other threats when they are neurologically impaired by lead toxicity. Basically this normally precise bird can be literally “flying drunk” and get itself into dangerous situations that would normally not occur. Birds admitted to the Wildlife Center that have measurable levels of lead are often seen with neurologic and gastrointestinal symptoms that impair the bird’s ability to survive in the wild. Droopy, neurologically inappropriate, emaciated eagles, hawks, owls, ospreys and other raptors are commonly admitted by wildlife veterinarians. Many of these birds are euthanized and of the birds treated a high number do not survive.
Attempts to treat and rehabilitate raptors and other bird species are made through chelation. Chelation is achieved when a substance such as Calcium EDTA is administered to patients to bind with lead to facilitate its excretion from the body. Treatment for wounds and other ailments acquired due to lead toxicity and supportive therapy are often needed. If chelation therapy is successful and the bird can be returned to health, many months of physical rehabilitation can be required before a bird can be strong enough to be returned to the wild.
What can be done about the threat of lead toxicity for our wild avian species? Proposals of a ban on lead munitions have met with much resistance. There are other measures that can be taken. Education is essential. Awareness of the effects of lead toxicity needs to become widespread in the community. Hunters need to realize that that deer they kill may also kill birds of prey. Fisherman need to understand that the lead sinker they just lost may kill a swan or duck. This does not mean that hunting in general, or even specifically lead ammunition needs to be banned. What this situation needs is better education that can promote measures that will curb this preventable toxicity.
There are alternative munitions that are made from non-toxic metals. Copper bullets are one alternative. A hunter can choose to use less toxic munitions that will not harm birds if ingested. Other methods include commitment to retrieval or burial of carcasses in the field. Removal or burial of carcasses or field dressing debris is optimal, but even covering this material with a heavy layer of brush can restrict a raptors access to contaminated flesh. Other measures to protect wildlife from lead toxicity can be designed and implemented if more minds work on the problem.
Conscious choices can be made by hunters and munitions manufactures to halt this toxic tragedy. Education and action is imperative to save our national bird and his colleagues from decimation by a completely anthropocentric environmental pollutant. Over the years regulations and measures have been implemented to reduce human exposure to lead in the environment. Our wildlife is an essential national and global resource that we must protect. Go forth and educate! Lest our national bird is to be replaced by the more lead resistant Turkey Vulture.