Emily Savage
BIOL 306
The Effect of Lead Ammunition on Bald Eagle Populations
The toxicity of lead has been documented in a large array of organisms with the harmful
effects causing bad health, poor reproductive success and, if ingested in a large enough quantity,
death. In the United States, waterfowl have been one of the more prominent groups affected by
lead poisoning, and many people have taken action to try and reverse this problem.
Unfortunately many people are neglecting or not noticing the lead poisoning that is occurring in
the terrestrial birds. There are several birds whose reproductive success is being threatened,
among these birds are the Cooper’s Hawk, European Kestrel, Japanese quail, ringed turtle doves
and American Kestrel (Fisher et al., 2006).
The Cooper’s Hawk will lay an egg with a higher concentration of lead if the adult has
higher levels of lead in its system, and if the European Kestrel has elevated levels of lead in its
system then there is be a good chance it would lay an egg with a thinner shell. The Japanese
quail is less likely to lay eggs, if the adult has high levels of lead, and the male ringed turtle
doves run a higher risk of testicular degeneration. Often in bird species with altricial young, such
as the American Kestrel, the body length, brain, liver and kidney weights will not develop
properly. There is also evidence to suggest that, in certain species, a certain sex might be more or
less affected than the other, like in the western marsh-harriers (Fisher et al., 2006). One of the
most notable of affected terrestrial birds is the California Condor. Due to the Condor’s incredibly
small population, many efforts have been made to bring it back from the brink of extinction.
However, according to Fisher et al. (2006) the birds that are most likely to get lead poisoning are
the raptors due to their consumption of game animals that have been shot with lead ammunition.
Lead ammunition should be banned in all states due to its detrimental effect on raptor
populations, and more specifically, bald eagle populations.
There are several different ways bald eagles can get lead from their environment. The
most common way for bald eagles to acquire lead is consumption of an animal’s remains left by
a hunter. Hunters who are after deer will leave offal piles at the kill site after they have gutted the
deer. Offal consists of the internal organs and entrails of a butchered animal, essentially it
includes everything except muscle tissue and bone (Finch et al., 2010). Offal piles are found all
across the United States with some areas having more than others. Wisconsin had about five
offal piles per km2 in 1992-2001 from just white-tailed deer hunting. This does not include the
number of animals that were wounded or escaped, which was about ten percent (Burnham et al.,
2006). In Minnesota there are about 200,000-250,000 offal piles left each year by deer hunters.
Montana’s wounding rates/losses are about 24%, Illinois is 21-24% and Indiana wounding
rates/losses are 17-32% (Butler et al., 2010). Roughly 90% of offal piles contain lead fragments.
This is because when hunters aim at a deer they are aiming at the thoracic cavity, which contains
the vital organs. The vital organs are often not desired by the hunter so they are left to
scavengers, such as the bald eagle (Burnham et al., 2006).
Hunters will also kill pests such as coyotes and ground squirrels. They do not collect any
part of these animals for consumption, so they leave the carcass where it fell. Lead poisoning in
bald eagles becomes more prevalent January-March in the Pacific Northwest. During these
months big game season has come to a close and the shooting of coyotes increases. The other
nine months of the year the bald eagles live closer to bodies of water, where their diet mainly
consists of waterfowl and fish. Once the winter months set in these bodies of water freeze,
forcing the bald eagles to find a new food source. A dead coyote is an easy meal that
unfortunately contains lead fragments (Finch et al., 2010).
Another way for bald eagles to obtain lead is consumption of waterfowl that have been
shot with lead shot or have ingested lead in some form, usually lead shot or fishing lures (Fisher
et al., 2006). The lead shot is often ingested because the waterfowl mistake it for a small pebble,
which they use as grit in the gizzard. Birds do not have teeth so the grit in the gizzard acts as
teeth by mashing up the food before it enters the stomach. Once the lead is in the gizzard it will
begin to degrade and be absorbed into the bodily tissues such as the liver, kidneys, brain and
bone (Campbell et al., 2008). At this point the waterfowl has lead poisoning, and if a bald eagle
eats the waterfowl, it could also get lead poisoning. (Fisher et al., 2006). The bald eagle could
also eat the gizzard of the waterfowl, which contains lead shot. Thereby introducing lead to their
system and increasing the chance of lead poisoning (Campbell et al., 2008).
A large number of waterfowl were exhibiting lead poisoning due to their consumption of
lead shot they mistook as grit. In response the United States began to phase out lead shot used in
waterfowl hunting. The final result in 1991 was a nationwide ban on using lead shot for
waterfowl hunting on all federal lands. However, many states, such as Minnesota, voluntarily
banned lead shot from state owned lands as well. Canada banned lead shot for waterfowl hunting
in 1999 (Cruz-Martinez et al., 2012). Now that lead shot has been banned, it is more likely for
bald eagles to ingest lead from upland game birds and mammals than from waterfowl. An upland
game bird is an American term that refers to any game bird that is not a waterfowl (Fisher et al.,
2006). Unfortunately after the ban against lead shot was put in place, researchers noticed that
there was no reduction in the number of bald eagles being admitted to treatment facilities for lead
poisoning. Most of the cases occurred during deer season (Cruz-Martinez et al., 2012). This
shows that many of the bald eagles were ingesting lead fragments from discarded kills rather
than eating waterfowl.
Between 1966 and 1984 there were a minimum of 77 bald eagle deaths (Abbott et al.,
1989). British Columbia had 37% of 294 sick, injured or dead bald eagles, all caused by lead
poisoning. Out of the 37%, 23% were subclinically exposed, meaning they had not begun to
show symptoms, and 14% were poisoned. In 1996, 10-5% of post-fledgling bald eagles died
from lead poisoning (Fisher et al., 2006). Fortunately not all exposure to lead results in death.
Death only occurs after repeated exposure if the bald eagle can get the lead out of its system via
regurgitation or defecation (Abbott et al., 1989).
Once lead has been consumed by an eagle it has three options. It can be regurgitated
immediately, which means the lead does not have to time to enter the eagle’s system. The lead
could remain in the eagle for an indeterminable amount of time, or it could dissolve and enter the
eagle’s bloodstream. Once the lead is in the bloodstream it can now be transported throughout
the eagle’s body, often getting deposited in the liver or kidneys where it can stay for several
months. The lead could also get deposited in the eagle’s bones where it can stay for several years
(Fisher et al., 2006).
Several factors go into determining whether an eagle will get lead poisoning; how long
the lead is in the eagle’s system, how often and for how long the eagle has been exposed to lead,
the eagle’s nutritional status before the lead exposure and the amount of stress the eagle is
receiving from its environment. The rate of lead absorption determines how quickly the eagle
will die (Fisher et al., 2006). In an experiment lead shot was given to several captive bald eagles
and the number of days between ingestion and death was recorded. The number of days before
death ranged between 10 and 100 with the median being 20. The eagles were able to retain the
lead in their systems for 0.5 to 48 days (Huffman et al., 1981).
The smaller the fragmented pieces of the bullet, the more surface area is exposed to
consumption, and once the eagle has consumed the fragments, the more surface area is exposed
to the eagle’s stomach acids. Shot gun pellets, despite their larger size, provide less surface area
for the eagle’s stomach acids to work on (Buskirk and Pauli, 2007). The pH of an eagle’s
stomach acid is very low, which means that any lead ingested is broken down very quickly, and
then gets absorbed. If a large volume of lead is ingested too quickly the eagle will die without
displaying any of the symptoms of lead poisoning usually shown by raptors (Fisher et al., 2006).
Bald eagles will display both internal and external symptoms of lead poisoning. External
symptoms include green, watery feces, weight loss, anemia and a drooping posture. Anemia is
when the body receives an inadequate amount of oxygen due to a lack of healthy red blood cells.
Lead poisoning will also result in the distension of the proventriculus, which is the glandular part
of a bird’s stomach that stores and aids in the digestion of food before it enters the gizzard
(Fisher et al., 2006).
Internal symptoms of lead toxicosis include neural degeneration, modification of kidney
structure and bone structure and inhibition of blood formation and nerve transmission (Burnham
et al., 2006). If there are low levels of lead in the eagle’s body it will affect the activity of blood
enzymes (Fisher et al., 2006). One of these blood enzymes is δ-aminolevulinic acid dehydratase
(ALAD). ALADs function is to hemoglobin content in red blood cells. Inhibition of ALAD is
used to help detect lead exposure (Hoffman et al., 1981). Eventually hematocrit and hemoglobin
levels may drop. Hematocrit is the volume percentage of red blood cells in blood. The immune
system is suppressed, which leads to a higher susceptibility to disease and infection. These will
leave the bird weak making it susceptible to predation and starvation (Fisher et al., 2006). These
symptoms may or may not appear depending on how much lead is consumed. If too much lead is
introduced too quickly into the eagle’s system, the eagle’s body does not have time to respond
and will die before showing any symptoms. When a bald eagle consumes lead fragments it is
ingesting a large volume of lead that has a great deal of surface area, allowing the lead to be
broken down and absorbed quickly (Fisher et al., 2006). Lead fragments present a serious health
risk to bald eagles.
Fragments are a result of bullets coming into contact with the target and breaking apart.
The reason bullets were designed to fragment is so they can cause the most amount of damage
possible. When the bullet fragments the little pieces are projected into the surrounding tissue,
causing a significant amount of internal bleeding, and if aimed properly, a great deal of damage
to vital organs. The biggest factors that play into bullet fragmentation are bullet material,
velocity and mass. There are a few bullet types that are designed for different guns and to react
differently upon hitting a target. The two big types are rapid expansion (RE) and controlled
expansion (CE). Other types include copper (Cu), muzzleloader (MZ) and shotgun slugs. The
latter two of which are both made out of lead (Butler et al., 2010).
RE bullets are designed to expand rapidly upon impact, which results in a large amount
of fragmentation (Butler et al., 2010). Bullet expansion can reach 40 cm in diameter around the
bullet’s path (Finch et al., 2010). The CE bullet is designed to resist fragmentation, which results
in the bullet maintaining much of its original weight, >90%. When a bullet maintains its weight
it is remaining in one piece rather than losing much of its material to fragmentation. Copper
bullets are made of either copper or a copper alloy. They are designed to not fragment upon
impact, retaining almost 100% of their initial weight and they are considered to be nontoxic. MZ
bullets and shotgun slugs are mostly made from lead, but due to their higher mass and being fired
at a lower velocity, they have less fragmentation (Butler et al., 2010).
An experiment was performed on euthanized, domestic sheep to look at the
fragmentation of different bullet types. Two types of RE bullets were used in the experiment,
both of which had lead throughout the core and had an advertised weight retention of 50%. Two
types of CE bullets were used, one of which had an advertised weight retention of near 100%
(CE1) and the other >90% (CE2). CE1 had copper in the front half of the bullet and a lead base,
while CE2 was a lead core bonded to a jacket. A shotgun slug made of 100% lead was used as
well as two types of MZ bullets, both of which had lead throughout the core. For all three the
advertised weight retention was not applicable. The velocity of the RE and CE bullets was in the
upper eight hundreds and the velocity of the slug and MZ bullets was in the mid to upper four
hundreds (Butler et al., 2010).
The sheep that were shot with the RE bullets and the CE2 bullets contained the largest
amount of bullet fragments compared to the sheep shot with the CE1 and Cu bullets. Also, the
sheep shot with MZ bullets and slugs contained fewer bullet fragments than the sheep shot with
RE or CE2 bullets. The latter trend is believed to be because of the higher mass of the slugs and
MZ bullets and their slower velocity. Based on the overall data, Cu, CE1 and MZ1 bullets
resulted in the least number of fragments (Butler et al., 2010). The most commonly used bullet is
the CE2 bullet, which has the lead core with a copper jacket. A bullet with a lead core and
copper jacket is designed to have the jacket separate from the core upon impact, or as the bullet
travels through the target (Cruz-Martinez et al., 2012).
Copper would be the best option for ammunition material in regards to the environment,
because it is less likely to fragment and even if it does, it is less toxic than lead (Burnham et al.,
2006). There are currently eleven non-toxic ammunition options approved for waterfowl hunters
now that lead shot has been banned (Fisher et al., 2006). The first alternative to lead shot was
steel shot, which was non-toxic, but presented a few problems. The use of steel shot disturbs the
ballistics of the gun because steel loses velocity and energy faster than lead, however, this was
eventually fined tuned (Barnes, 2009).
Steel is a much harder metal than lead, so it caused the gun barrels to wear down faster,
and it would clog the choke because it would not compress like lead. Steel also would not
fragment upon impact with the target because it is so hard, which meant that the game would
very likely only be injured and escape, only to die a mile away where the hunter might not be
able to find it. However, the fine tuning of the ballistics to increase the velocity fixed this
problem (Barnes, 2009).
Today the most used metal for shot is bismuth, followed by tungsten with a polymer, then
tungsten with iron and finally, steel. Bismuth is very popular because it acts like lead, but
without the toxicity. This also means that the barrel of older guns will not get worn down as
quickly. Tungsten is a much heavier and harder metal than lead, so in order for it to be usable, it
must be “watered down” using iron, steel or a polymer (Barnes, 2009). Unfortunately, even
though lead shot has been banned, other forms of lead ammunition are still very popular.
Bald eagles may not be currently experiencing as much of a threat from lead ammunition
as they experienced from DDT in the 1900s, but it still poses a very real threat to their existence.
Bald eagles ingest lead from a large array of sources, the most common being offal piles left by
hunters, usually during deer season. Once ingested the lead can leave via regurgitation or
defecation, or be retained. If retained, the lead will be adsorbed into the eagle’s system and the
symptoms of lead toxicosis will appear. Externally these include green, watery feces, weight
loss, anemia and a drooping posture. Internally the eagle will have trouble with vitamin
metabolism and decreased activity of blood enzymes. Lead can be retained in a bald eagle’s
system for 10 to 100 days before death occurs. However, ingestion of lead can be avoided if
more hunters would use bullets that are non-lead or that are designed to not fragment.
Bullets that resist fragmentation are called controlled expansion bullets and retain 90100% of their initial weight after impact. Unfortunately rapid expansion bullets are more popular
because when a bullet fragments upon impact with the target, the fragmentation makes for a
quicker kill. Other bullet types, beyond controlled and rapid expansion bullets, include copper
and muzzleloader, copper being the most environmentally safe bullet. Alternative metals to lead
in shot include bismuth, tungsten and polymer, tungsten and iron, and steel. Alternate
ammunition to lead has been around for years, and yet countries still refuse to phase out lead
ammunition. Bald eagles are not the only terrestrial birds being affected by consumption of lead
ammunition, and some of the affected birds could be endangered, like the California Condor.
These birds have the chance to be saved, but first governments across the world need to pass
laws prohibiting the use of lead ammunition, because whether hunters know it or not, they are
causing excess mortality by continuing to use lead as a primary ammunition.
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