Lead Poisoning - Part III


Commentary by Sanford R. "Sandy" Wilbur

28 April 2014

In January 2014, I tried to re-open the discussion of California condors and the role of lead poisoning in their recovery. I contacted by e-mail some 50 people who are now, or have been in the past, involved in efforts to increase the condor population. I laid out my concerns (see "Lead Poisoning I" and "Lead Poisoning II"), hoping to get some feedback (positive or negative), and hoping to find that more problem-solving was going on than I was aware of.

As a "discussion," the effort fell pretty flat. Only half a dozen or so people responded to me individually or to the collective group of 50. (Maybe I provoked some additional interchange between individuals; I hope so.) Only a few of the few total had substantive comments. But, only one responder came right out and said the issue was "not worthy of any further effort," which I hope means that some of the others do think there is more to learn and more to do.

The concerns I shared with the group can be re-stated in two basic questions. GIVEN, that some level of lead is found in the blood of almost every condor sampled, and that lead has been diagnosed as the cause of death in some condors: (1) is the source of lead contamination known? and (2) how big of an issue for condor recovery is lead contamination? I'll look at both those questions again, below, but first, a quick review of how we got to this point.

* * *

In their popular book on the condor published in 2000 [1], Noel and Helen Snyder concluded (page 252) - a conclusion based on three condors diagnosed as having been poisoned by lead - that lead poisoning was "potentially the most important mortality problem faced by the species." But the support for their claim was not particularly compelling. Here are just a few of their comments that I picked out for a review I did of their book in "The Condor" in 2002 [2]: (page 75) "if these condors were poisoned (which does not seem unlikely);" (p. 76), lead poisoning in the 1980s was "very possibly" caused by hunting; (p. 93), some deer carcasses "were presumably contaminated" with lead; (p.152) the Snyders were "reasonably confident that a substantial portion of the species' diet in the fall was hunter-shot deer;" and (p. 164), a lead rifle slug found in a condor nest cave "could conceivably have been responsible for the poisoning of generations of condor nestlings." I know that we often simplify science for presentation to the general public, but this seems to go well beyond mere "dumbing down."

Later attempts to define the issue have been equally obscure and questionable. The majority of the reports I reviewed on the subject (even ones of recent origin) are rife with phrases like lead poisoning being "strongly suspected," or the disappearance of condors being "plausibly attributable" to lead poisoning. Similarly, condors are said to have died "under circumstances that implicate lead ammunition," disappearances of condors are "associated with" lead sources, and condors are "thought to have fed" on lead contaminated food. All told, this doesn't come across as very good science.

Other writings by the Snyders make it sound like they felt they had identified a major source of condor mortality, and that they were positive that deer hunting was the culprit. Perhaps they were only speculating, and can't be entirely blamed for what has happened - and not happened - since then, but the result was that no one looked beyond their speculations, and deer carcasses and gut piles left by hunters became THE PROBLEM for condors. When a 2008 "blue ribbon panel" concluded, with little additional evidence [3], that "there is now widespread consensus and overwhelming evidence that poisoning due to ingestion of spent lead ammunition in carcasses and gut piles currently precludes the establishment of viable populations in the wild," they effectively killed any interest in finding a source of lead that might not be related to hunting, and killed any interest in a serious study of the long-term effects of the lead levels in condors. Since the Snyders' pronouncements on the subject, every effort to reduce lead in the condors' environment has been related to hunting. The failure of any of these efforts to reduce the lead levels identified in condors' blood should lead to the conclusion - or at the least strongly suggest - that "the treatment" does not fit "the disease."

* * *

My comments below apply mostly to California, as the Arizona-Utah condor situation is quite different. There does seem to be a significant lead problem in that condor population, and the problem does seem to be strongly linked to big game hunting activity. Livestock appear to be quite sparse over much of the area, and (from preliminary figures given to me by the Arizona people) big game carcasses (deer and elk) make up about two-thirds of the large mammals associated with condor feeding. Also, considering the actual number of big game carcasses found, the problems of poaching and wanton waste must be extreme compared to California, greatly increasing the chances of condors feeding on carcasses containing lead.


Even after the failures of reducing lead levels in condors, most of the current condor workers seem wed to the idea that deer hunting (with some pig hunting and small mammal shooting thrown in) is the principal source of the lead that condors are acquiring. Despite observations going back to the 1930s that deer provide a relatively minor amount of condor food, little effort has been put into finding out what condors are currently eating, or in finding out if the foods they are eating are actually contaminated with lead. The few efforts that have been made to get actual feeding records seem to confirm deer hunting's relative lack of importance. Ron Jurek, long-term California Department of Fish and Game biologist and one of the people with the longest tenure investigating condors, compiled some 90 feeding records and found that cattle and sea lions outnumbered deer, and that most of the deer were road kills, depredation kills, stillborns, or other non-hunting casualties [4]. A probably statistically-insignificant study of 31 feeding incidences was described in the 2012 annual report from the Hopper Mountain National Wildlife Refuge Complex [5] . They noted: "The most common types of carrion were cow, deer, and pig." Even this statement is misleading. Cattle amounted to more than twice the number of deer, and pigs were almost double deer. If you add cattle, sheep and horses, livestock carcasses amounted to 52 percent of finds (which I assume is about 16 of the 31 observations), while deer totaled 16% (5 deer?). Pigs made up 26% (8 animals), and there was apparently one elk and one coyote. The report summary does not mention the times of year these observations were made, nor does it mention how many might have been shooting-related.

In addition to an apparent lack of understanding of deer populations, deer habits, and deer hunting statistics, the current condor workers seem to harbor a number of other misconceptions about condor feeding habits and the possible effects of hunting.

1. Several studies have tried to estimate the number of various types of carcasses available within the condor range, and what percentage of those might actually contain lead [6, 7]. Even if the estimates of numbers or risk could be shown to have some degree of reliability, they would constitute a major overestimate of what is actually available to condors.

a. Condor use of what we consider "condor range" is actually quite limited, spatially. Historically, condors followed very specific travel routes and congregated in very limited areas at different times of year. Much of their "range" was only sparsely used at any time of year. That the zoo condors are developing similar traditions is shown clearly in reports such as the 2010 U. S. Geological Survey "Analysis of California condor use of six management units" [8]. In other words, only a fraction of carcasses of all kinds and arising from all sources would ever be seen by a condor, let alone eaten.

b. Even if a condor was in the vicinity of an animal carcass, there is only a small chance that particular carcass would be food for condors. Because of their wing-loading compared to other avian scavengers, condors can neither soar as early in the day or as late as their scavenging competitors. The extent of foraging is especially limited during fall and winter hunting seasons, when daylight is at it minimum. Animal carcasses, particularly those of small mammals, that become available early in the day are often consumed before condors even depart their roosts. Those that become available late in the day, after condors have returned to their roosts, are consumed by late foraging birds and (especially) coyotes and bears. This is especially true of gut piles. Even if condors find a food source late in the day, and choose to roost nearby overnight (which sometimes happens), there is no guarantee that coyotes won't have completely stripped the carcass overnight, or that a bear won't have dragged it off into the brush. (I'm not speaking hypothetically; ten years of supplemental feeding studies showed me that one or the other is of regular occurrence. See "Bird and Mammal Activity," on this website; also references 9 and 10.)

2. The importance of small mammals, particularly those that are shot, is greatly overstated. Although a condor will potentially eat any mammal, most small animal carcasses are consumed by ravens, turkey vultures, coyotes, and golden eagles. One correspondent opined that condors eat ground squirrels "like candy;" actually, condors seldom consume ground squirrels, mainly because other more efficient scavengers get to them first, but also because from an energy utilization standpoint, landing for even a few ground squirrels in one location would not be efficient. In the distant past, there were occasional times when large numbers of ground squirrels or kangaroo rats died above ground from poisons; condors did sometimes feed on them, although there are only a few concrete records. I haven't heard of any such occurrences in many years. In any event, those would not have been sources of lead.

One correspondent gave what I think is a very clear picture of why most small animal shooting does not pose a lead poisoning threat to condors: "Small game hunters (squirrels and rabbits) regularly remove the entire animal from the field, possibly gutting it but that's not much for condors to find and eat, especially before the ravens see it or the turkey vultures smell it... All varmint shooters I knew (and there were lots of them) used small caliber/high velocity rifles such as 220 Swifts, 223s, and up to .25-06s. When a bullet hits a small rodent it explodes, both the bullet and the rodent. Even a .22 long rifle will go totally through an animal's body. It's highly unlikely there is much lead residue left and the scattered body parts are primarily magpie, raven and ant food. Coyote hunters remove the carcasses more often than not, either to skin for pelts or for bragging rights."

3. One responder to my questions thought that high lead levels found long after the deer and pig hunting seasons could occur because "condors could continue to scavenge on carcasses and gut piles with lead long after the hunting season had ended." Actually, gut piles are unlikely to last more than a few hours before being consumed by avian, mammalian or insect scavengers. It is remotely possible that a deer or pig that had been wounded during the hunting season might survive and die from some other cause later, and be consumed by condors; however, it would seem a highly unlikely occurrence. The hides of shot animals might lie in place for a long time, but condors do not go after dry hides. Lead deposited in lake bottoms may affect waterfowl for years, but lead in a mammal carcass is either ingested or it isn't; there is no lag time.

4. Livestock and sea lions are more often documented as condor food than are deer and pigs. Livestock are shot regularly by ranchers (euthanasia), poachers, and vandals [4]. Between 1992 and 2009, the Marine Mammal Center amassed records of nearly 500 marine mammals (mostly sea lions) that had been shot. They considered this a very small sample of the actual numbers shot [11]. As livestock shooting is not a hunting activity, and since shooting marine mammals is already illegal, neither source of potential lead is affected by either the Ridley-Tree legislation, or the more extensive law passed by California in 2013. I find no evidence that the current condor people have been seriously considering either type of shooting as a lead poisoning problem for condors.

5. Several people suggested that the Ridley-Tree lead ammunition ban was not effective in reducing condor lead levels because it was not strictly enforced. No doubt this was true for a year or so, as hunters took the chance of using old ammunition stockpiles, and as game wardens moved into the program with some leniency. Although the California Department of Fish and Game reported in February 2009, after one season of Ridley-Tree, that hunter compliance was at 99 percent, that seems unduly optimistic. Nevertheless, any period of grace would have only lasted one or two seasons, old ammunition stores would have been used up, and fear of being apprehended would have increased. Also, there were some immediate changes that would have had a significant effect on the amount of lead potentially available to condors from hunting. For example, the Tejon Ranch, a major condor feeding area, after the passage of Ridley-Tree enacted an immediate ban on all lead-based ammunition (both for hunting and other ranch uses) on their 200,000 acres [12]. (Some have questioned how real and effective the Tejon ban has been, but from many years of working closely with Ranch personnel, I can testify that their hunting programs have been among the most highly supervised and controlled in the entire country. If they say they aren't allowing lead ammunition, they aren't.)

Countering claims of non-compliance with the lead ban is a study asserting major decreases in lead levels in golden eagles and turkey vultures following just one hunting season with the Ridley-Tree restrictions [13]. Carrion from large mammals is not a principal food of either species, even in winter in California. Because of the mildness of the California winters, small mammals - both alive and dead - do not show the marked decreases they do in harsher parts of the country, so eagles are not forced to carrion. Compliance with the lead ammunition ban would have to be extremely high in the areas sampled to obtain the lead reductions claimed.

* * *

I think it is fair to say that any potential sources of lead in condors other than from ammunition (lead in paint, in the air, in the soil, etc.) are at most minor contributors to any lead accumulations. Also fair to say, I think, is that if deer and/or pig hunting were the source(s) of a major share of the lead found in condors, significantly lower levels in condor blood should be apparent after this many years of Ridley-Tree. That lead levels have not declined, and that lead levels are similar at all seasons of the year (not just in response to the principal hunting period) seems ample proof that the principal sources of lead poisoning have not yet been discovered and managed. Shouldn't this be top priority if lead poisoning is the threat to reintroduction and recovery that it is claimed to be?

I know that getting actual proof of what condors are eating is not easy. In my 10+ years of field study, my personal discoveries of condors on a carcass were relatively few. Most records came to me from others - ranch personnel, Forest Service people, etc. - who were on the ground more often and in many more places than I could be. A network of volunteer observers takes time to establish and maintain, but the extra information acquired is well worth it [14]. I assume such a program currently exists, although I haven't seen any written evidence of it.

There is at least one experimental study of condor food habits in progress, an analysis of the animal carcass DNA showing up in fecal samples of wild condors captured for other purposes [15]. This is good, innovative work, and I hope funding can be found to make it an ongoing program. Still, I wonder if all those tagged and radioed condors can't be put to better use. As I understand current procedures, there is very little "boots on the ground" monitoring of the radioed birds; their locations are identified by satellite, and clusters of "hits" used to denote possible feeding "observations." It can be several days before such patterns are evident from the collected data, meaning actual follow-up on the ground is seldom possible [16]. It seems little more is being learned about food habits from telemetry and the ability to identify individual condors than we learned in the '60s and '70s by wandering around in the hills hoping to find a few condors to watch. There must be more that can be made of these resources.


The Snyders' indictment of deer hunting as the main source of lead contamination in condors was premature, and probably incorrect. The dramatic pronouncement of Meretsky and Snyder [17] that any condors having high levels of lead in their blood "are best considered mortalities," if not subjected to chelation therapy, is untrue. That said, it is true that condors carry high levels of lead in their systems, that the lead sometimes proves quickly fatal, and that sometimes it eventually proves fatal. Lead may interfere with other important biological processes without killing the condors, but I'm not sure if this is proven, or conjecture based on the effects of lead on other organisms.

However, it is also true that condors with high lead levels have continued to live a number of years after being diagnosed, and have stayed successfully reproductive. Condors have survived lead levels that would have been fatal to bald eagles. Also, some of the studies showing high rates of mortality from lead in captive eagles and vultures - the results of which have been extrapolated to suggest what happens to condors - have subjected the captive birds to repeated high dosages of lead, not representative of how condors likely obtain and respond to lead in the wild.

I don't think that the current lead levels in condors preclude successful reestablishment of condors in California or elsewhere on the Pacific Coast. I can't prove that, and I could be wrong. The problem is, the people who have been working with the condors for the past twenty years can't disprove it. As one of my correspondents (one well-versed in chemistry, toxicology and lab procedures) put it, the direst pronouncements about lead poisoning "may well be correct but not based on a scientific rationale... Without a better estimate of blood levels that are potentially lethal, it is hardly possible to state that without treatment the birds will surely die. With so much manipulation - even if justified - and no controls or control situations anywhere, no scientific conclusions can be made from the current treatment program."

Looking once more at the deer hunting situation in central and southern California in the 1950s and 1960s, there is absolutely no question that there were many more deer in the region than there have been since. There were many more hunters, and many more deer killed than at any time either before or after that period. I don't know if there are any actual estimates of deer cripplings, unretrieved kills, and general wanton waste during those years, but I doubt that anyone working in the field during that time would have trouble believing that the number of potentially lead-infected deer carcasses left in the area was much, much greater than at any time since. Yet, there is no evidence of a major decline in condor numbers during that time of maximum use of lead ammunition in the area. Condor numbers decreased, but no more than one would expect from the variety of causes that had kept mortality in the population somewhat higher than natality since the early 20th Century. (It's unfortunate that no one was actively studying condors during those years, but we have a substantial file of individual observations made by game wardens, Forest Service personnel, ranchers, etc., including documented losses of condors to shooting and other causes.)

One conclusion that might be drawn from the fact that the condor population did not crash during the period of highest deposition of lead from ammunition is that lead from hunters' bullets was not a principal cause of lead in condors. I think a more likely conclusion would be that condors did indeed accumulate lots of lead, but that the load of lead that condors accumulated was not as lethal or as biologically impairing as is currently believed.

* * *

The actual role of lead deposition in long-term condor deaths or debility is not an unanswerable question. To repeat what I said in my questions to the field: The long-term effects of high lead levels on condors in the wild could be easily tested by setting up a control group among the released birds, those birds not captured and handled as often as the others, and not chelated when lead levels in blood reached the danger (to human children) level. Some condors might die from such an experiment, but more condors are being produced now than can be used in ongoing release programs (and) the potential sacrifice of some condors now could clarify how much we really should be worrying about lead, and might make it possible to have a successful condor reestablishment program without the exorbitant costs of the current ones.

My suggestion did receive some support from those who responded. One said: "I completely agree with your comments about the need to do research on captively produced condors, even if it results in some fatalities. We can produce all the condors we want in captivity, so why not use some of them for critical research?"

Another gave a more specific proposal: "What would be the argument(s) against a moratorium on the chelation treatments for, say two years - and only in California - on only in either central or southern California? A moratorium of two years would provide solid survival data for both adults and juveniles, necessary for any valid population model."

There might also be a way to look back and compare the lead levels in condors before, say 1950, with levels during the peak of deer hunting the 1950s and 1960s), and with what is being recorded currently. My chemistry is pretty weak, but I am told that lead levels in bones and feathers may provide more meaningful information that that being obtained from blood. If museum mounts, skins or skeletons could be used to study either bone or feather lead levels, there are several hundred available from before 1950. There are fewer specimens from the 1950s and 1960s, and most are skeletal only; even so, there are about 20 specimens that might be used for bone analysis, seven or eight of which also have feathers preserved. I know the locations of all those specimens.


Although I haven't had any direct involvement in the condor program for many years, I've invested much of my adult life in studying the species in the wild, in museums, and in libraries. Although my name and those of my co-workers from the 1970s are almost never mentioned in connection with the captive breeding and release program, without us the program would not exist, and condors would almost certainly be extinct. This isn't bragging or undue credit-taking. Trapping condors, propagating them in captivity, and releasing them to the wild did not just happen. It took us years of developing the case, then "selling" it biologically, politically, administratively, and with the public at large. Pushing for a biologically and publicly credible program I would like to see the program succeed.

I'd also like to see the discussion get back to what condors need for survival, rather than how we get all the lead out of the environment, or (depending on your point of view) how we protect hunting/get rid of hunting. The primary purpose of any action concerning condors and lead should be to maximize the potential for success of the recovery program. If other agendas are helped or hurt by condor recovery actions, that should be a secondary consideration.

I don't know enough about the current workings of the condor program to know why some basic research on food habits and the actual toxicity of lead can't get done. Several respondents told me that, although good efforts are being made in the various recovery subprograms, there is no significant coordination between the various groups. If true, that would make it difficult to get projects approved and funded that encompass all the subgroups and address more than local situations. It would seem like the U. S. Fish and Wildlife Service, with ultimate authority over endangered species, would be the one to serve as the catalyst for the needed studies.


1. Snyder, N. F. R., and H. Snyder. 2000. The California condor : a saga of natural history

and conservation. San Diego: Academic Press.

2. Wilbur, S. R. 2002. Book Review: The California condor, a saga of natural history and

conservation. Condor 104(1):222-226.

3. Walters, J. R., S. R. Derrickson, et al. 2008. Status of the California Condor and efforts

to achieve its recovery. The American Ornithologists' Union and Audubon California.

4. Jurek, R. 2005. Remarks supplied to the AOU "blue ribbon panel" on the California condor recovery program.

5. Brandt, J. 2013. California condor recovery program, 2012 Annual Report. Hopper Mountain National Wildlife Refuge Complex, U. S. Fish and Wildlife Service.

6. Fry, D. M., and J. R. Maurer. 2003. Assessment of lead contamination sources

exposing California condors. Final report. California Department of Fish and Game.

Sacramento, California.

7. Finkelstein, M. E., et al. 2012. Lead poisoning and the deceptive recovery of the critically endangered California condor. Proceedings of the National Academy of Sciences 109(28):11449-11454.

8. Johnson, M., J. Kern, and S. M. Haig. 2010. Analysis of California condor (Gymnogypscalifornianus) use of six management units using location data from global positioningsystem transmitters, southern California, 2004-09: initial report. U. S. GeologicalSurvey. Reston, Virginia. Open File Report 2010-1287.

9. Wilbur, S. R., W. D. Carrier, and J. C. Borneman. 1974. Supplemental feeding programfor California condors. Journal of Wildlife Management 38(2):343-346.

10. Wilbur, S. R. 1978. Supplemental feeding of California condors. Pages 135-140 in:Temple, S. A. (editor), Endangered birds: management techniques for threatenedspecies. Madison, Wisconsin, University of Wisconsin Press.

11. "Marine mammal gunshot victims," posted on the website of the Marine Mammal Center - http://www.marinemammalcenter.org/science/top-research-projects/gunshots-and-more.html

12. Hill, H. J. 2009. Taking the lead on lead: Tejon Ranch’s experience switching to non-lead ammunition.Abstract in R. T. Watson, M. Fuller, M. Pokras, and W. G. Hunt (Eds.). Ingestion of Lead from SpentAmmunition: Implications for Wildlife and Humans. The Peregrine Fund, Boise, Idaho, USA.

13. Kelley, T. R., et al. 2011. Impact of the California lead ammunition ban on reducing lead exposure in golden eagles and turkey vultures. PLoS ONE 6(4):e17656.

14. Wilbur, S. R. 1978. Volunteer participation in California condor surveys. WildlifeSociety Bulletin 6(3):157-159.

15. Correspondence with Katherine Ralls, February 2014.

16. Correspondence with Joseph Brandt, February 2014.

17. Meretsky, V. J., N. F. R. Snyder, et al. 2000. Demography of the California condor:implications for reestablishment. Conservation Biology 14(4):957-967.


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