Lead bullets in carcasses and gut piles pose lethal poisoning hazards to carrion feeders. Among the creatures most at risk are the endangered California condors that frequent Grand Canyon National Park and other areas of Arizona and Utah.

Rifles used to shoot elk, deer, coyotes, and other game animals or "varmints" typically use ammunition with lead bullets at the business end. It's not difficult to understand why. Lead bullets (usually clad with copper, except for the tip), have favorable ballistic properties, can be manufactured fairly cheaply, and are sold throughout the U.S.

Some lead bullets, fragments, and residues inevitably end up in gut piles (internal organs removed during field-dressing) and in the carcasses of hunter-killed animals that are not recovered. Cold and snow can enable these lead-tainted remains to persist in the environment until after spring thaw.

Unfortunately, lead (chemical symbol Pb) is a potent neurotoxin that accumulates in bones and soft tissues. When humans, animals, or birds accumulate excessive amounts of this heavy metal -- whether by swallowing it or breathing it -- the consequences are nerve system damage, brain disorders, blood disorders, and related problems. Because lead is readily absorbed into the bloodstream, nearly every organ and system is adversely affected. Harmful effects can range from minor to catastrophic. If the damage is severe enough, especially in acute cases (large amount of lead taken into the body in a short period of time), the victim ends up permanently disabled or dead.

The lead-tainted carcasses and gut piles that hunters leave behind pose a hazard to carrion eaters and the many omnivorous species who feed opportunistically. While many questions about this hazard remain unanswered pending the results of ongoing research, there is no doubt that the damage done to wildlife is significant. For one thing, the animals and birds killed or severely injured by lead poisoning are unable to fill their ecosystem roles, insuring that the adverse impacts will extend well beyond the victims themselves. For another, some of the harm is inflicted on rare or uncommon species that can ill afford the loss of even a few individuals, especially breeding-age adults. The victims of lead poisoning even include federal- or state-listed threatened and endangered species.

A good case in point is the California condor, a critically endangered carrion-eating species that was only recently rescued from the brink of biological extinction. Great effort and expense has been invested in captive breeding programs that have raised the California condor population from a scant 22 individuals in 1987 -- all in captivity -- to a comparatively robust population of 381 today, including 192 birds in the wild.

As of last month, 76 California condors (including three that haven't been seen since last spring) were in Utah and Arizona, two states where sport hunting is popular and many carcasses and gut piles accumulate each fall. Now is a dangerous time for the condors, and the lead poisoning danger will persist until after the last of the winter-frozen carcasses and gut piles are gone next spring.

Sadly, even a single carcass or gut pile with lead in it has the potential to seriously poison several condors. Condors are group feeders, often flying considerable distances to join other birds feeding on a carcass. It doesn't take much lead in a carcass to do great harm, either. Bullets commonly break up into many small fragments, especially after striking bone, and consuming just one or two of these fragments can make a bird sick.

The threat is a potentially lethal one. According to the Arizona Game and Fish Department, lead toxicity is the leading cause of condor deaths in the Arizona reintroduction program. As of last year, lead poisoning was known to have caused eight condor deaths in Arizona and was implicated in two other condor deaths in that state.

Condors in Arizona are trapped twice each year so they can be tested for lead poisoning and treated if necessary. By March 2009, nearly a decade after the testing program began, biologists had found lead residues in 49 condors (most of which had been exposed multiple times) and employed chelation treatments to remove dangerously high levels of lead from the blood of 31 birds. There is little doubt that some of those poisoned birds would have died without treatment.

During the fall hunting season, and until the first heavy snows of winter arrive, condors hang out in the Kaibab Plateau region of northern Arizona and in southern Utah. Using radio tracking and visual observation, wildlife biologists have confirmed that condors currently foraging there have found carcasses with lead in them. Now they are crossing their fingers and hoping that the far-ranging condors, including birds recently released in the Grand Canyon vicinity (four at Vermillion Cliffs in September) will not be seriously impaired and in need of emergency treatment.

Of course, restoring poisoned birds to health does not address the root cause of the lead problem. Only reducing the birds' exposure to lead does that. Since environmental sources of lead pose a negligible risk to the condors, eliminating lead bullet use in condor country could virtually eliminate the lead poisoning threat to this magnificent bird (and, of course, to the other creatures that feed on carcasses and gut piles). The cooperative efforts of sportsmen's groups, ethical hunters and government agencies, including the distribution of free non-lead (copper) ammunition to hunters in some areas, have already substantially reduced the use of lead bullets. In addition, hunters who continue to use lead bullets in condor country are being urged to remove shot animals and gut piles from the field, or if this is not possible, to hide them or remove bullets and surrounding flesh that may contain lead fragments.

Postscript: The federal ban on lead shot use in waterfowl hunting that went effect in 1991 has been credited with preventing the premature deaths of millions of waterfowl that ingest shotgun pellets while feeding.