Lead Poisoning - Part I


Sanford R. Wilbur
October 2013

In 2007, action by the California Fish and Game Commission resulted in regulations that banned the use of lead ammunition for hunting deer, wild pig, elk, black bear, pronghorn antelope, and (in some circumstances) coyote within the range of the California condor. The hope was that there would be a reduction in the potential for lead poisoning of condors by eliminating lead that could be contained as fragments within carcasses of hunted big game species.

The legislation leading to this ban directed the Fish and Game Commission to "issue a report on the levels of lead found in California condors. This report shall cover calendar years 2008, 2009, and 2012. Each report shall be issued by June of the following year. "

The 2008 and 2009 reports were received by the Commission on time, in June of 2009 and 2010, respectively. As might have been expected, not enough time had passed since the ban to shows its effects on the condor population. The report due in June 2013 (apparently just received by the Commission), showing five full years of the ban, should provide some useful information on how effective the lead ammunition ban has been toward protecting condors.

I understand that the new report is to be discussed at the 6 November 2013 Commission meeting in San Diego. With that in mind, I've reproduced below the section of my recent book on the history of condors. It might help as a discussion stimulator, regardless of the results apparent from the lead ban.

[You will note that, in the section reproduced below, there is very little comment on the lead poisoning situation after the 1980s. This is because the book is about causes of decline in the historical population of condors, which was gone by the mid-1980s.]

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(From: Wilbur, S. R. 2012. Nine Feet from Tip to Tip: the California Condor through History. Gresham, Oregon: Symbios Books.)

Between 1982 and 1985, three California condors were diagnosed as having died from acute lead poisoning [37]. No California condor is known to have died of lead poisoning prior to that time, but few tests were made that would have identified that problem. As early as 1969, lead poisoning had been found in a captive Andean condor, and the authors of the study had warned that California condors might be susceptible [38]. A California condor that died of a gunshot wound in 1976 had a "somewhat elevated" lead level in one tarsus, but low lead levels in liver and kidney. The investigators ruled out recent high level exposure to lead, and conjectured that the source may have been some past high level exposure or perhaps a chronic low lead level [39]. Between 1995 and 2007, two of the captive-reared condors that had been released in California died of lead poisoning, while several others showed very high lead levels in their systems [40]. The number of deaths attributed to lead was much higher in the zoo-released condors in Arizona [41].

The source of lead in condors (past and present) is almost certainly fragmented bullets ingested from the mammal carcasses fed upon by the birds [42]. This type of ammunition came into general use after about 1890. With almost 100 years of exposure to such a potentially lethal agent, it seems inevitable that condors died of lead poisoning throughout the 20th century. (For example, the three condors discussed above [i.e., earlier in this chapter, not reproduced here] as possible victims of "1080" showed symptoms that could have been attributed to lead poison.) Still, there are some troubling questions that need answers before even an educated guess can be made concerning the magnitude of historical losses to lead poison [43].

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All recent discussions of lead poisoning in condors have identified mule deer - either full carcasses of deer shot but not retrieved, or the "gut piles" left when hunters field dress their kills - as the principal source of contamination [44]. This is a curious conclusion because all researchers prior to 1980 concluded that deer were a secondary food source for condors, far behind cattle and sheep. In the 1930s and 1940s, Koford reported that "the principal food today is Hereford range cattle," with "approximately half of all instances" of feeding seen by him, reported by others, or cited in literature involving beef cattle, principally calves. Deer were included in the other half, but so were sheep, ground squirrels, horses, and a variety of small mammals [45]. In the 1960s, the McMillan brothers found that "condor food continues to consist chiefly of the carcasses of cattle and sheep, especially the former" [46]. In the 1970s, I observed an even greater shift to cattle as sheep numbers decreased in the condor range [47]. I also cited the findings of deer experts who noted that dying deer tend to drift toward canyon bottoms [48]. There, steep terrain and heavy brush would interfere with the ability of condors to see many of the carcasses (since condors find food by sight, not by smell) and also to reach them (because of their large size and wingspread). Even the originators of the ideathat most contamination was coming from deer carcasses could only say (without actual observation) that they were "reasonably confident that a substantial proportion of the species' diet in the fall was hunter-shot deer" [49].

The idea that condors feed heavily on gut piles came from the same writers, referring (without details) to "many records of birds feeding on deer gut piles or on crippling-loss deer" [50], and asserting (again, without details) that gut piles "are well known as favored food for condors" [51]. Yet Michael Fry, in a detailed evaluation of the threat of lead to condors, concluded [52]: "There are no documented feeding records of condors using gut piles, with the exception of gut piles of domestic pigs deliberately placed in the field by the MacMillan [sic] brothers... in the 1950s." Apparently there are a few unpublished observations from southern California [53], and condors in Arizona have been seen at gut piles on a number of occasions [54], but the overall record is definitely slim.

Gut piles seem to me an unlikely source of regular condor food. As condors find food by sight, not by smell - and gut piles don't look like "food" - condors likely find most gut piles by seeing other animals at them. "Gut piles do not remain in the field for long, as both mammalian and other avian scavengers quickly consume them" [55]. By the time condors - late risers because of their high wing loading - see other scavengers feeding, most of the gut piles would be gone.

While it has been generally found that lead levels in condor blood samples in California are highest during deer hunting season, they have also been found to be elevated in the same areas six months before and after deer hunting season [56]. (Of the three native condors diagnosed as dying from lead poison, one died in March and one in April, months after the end of deer hunting season.) Lead levels in blood drop quickly to baseline levels if the bird is not re-exposed (half-time 13 days, very high levels reduced to baseline in 30 days or less) [57], so condors must be acquiring lead in substantial amounts clearly not the result of deer hunting.

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The historical record of deer hunting also raises questions. While condor numbers were decreasing during the mid-20th century, nothing suggests an especially precipitous decline during that period. Yet, deer kill within the condor range, which had held relatively steady through the 1930s and 1940s, doubled in the 1950s and 1960s. By the mid-1970s, the kill had returned to pre-1950 levels, and continued to decrease until by the early 1990s the annual kills were only two-thirds those of previous 15 years. There has been no increase in the years since. These are not small fluctuations. Between 1950 and 1969, the annual deer kill in condor range probably exceeded 15,000; before and after, it was perhaps 8,000 annually, and by 1980 less than 5,000. In the 1980s, half of the kill each year was in San Luis Obispo, Monterey, and San Benito counties, areas seldom visited by the surviving condors [58]. Most of the deer that are shot would not have become food for condors, only the "gut piles" left by hunters and those deer that were shot but went unrecovered. This "crippling loss" varies from area to area, but averages perhaps 20 percent of the total kill [59]. Doing some very rough math to determine the potential availability of lead from deer hunting:

- During each hunting season in the 1980s - in Santa Barbara, Ventura, Los Angeles, Kern, and Tulare counties, combined - perhaps 500 deer carcassesand 2,500 gut piles would have been left on the range.

- Each hunting season in the 1950s and 1960s, there would have been 3,000deer carcasses and 15,000 "gut piles" available, and many more condors tofind them.

If most lead received by condors was being ingested from deer carcasses and "gut piles," the chances of a condor receiving recurring dosages of lead would have been much greater in the 1950s and 1960s than in the 1980s. Yet - as noted above - there is no evidence of a precipitous drop in the condor population during the early period. It seems that there must be more to the story. One probability is that deer hunting has not been the main source of lead available to poison condors. For example, the chemical composition of the lead found in condor blood samples is the same as that found in deer hunting ammunition [60], but this is the same type ammunition used by ranchers to kill sick or injured livestock. Many agencies distribute pamphlets describing methods of euthanasia; a typical paragraph on the technique reads [61]: "A .22 caliber long rifle, 9mm or .38 caliber gun can be used. The muzzle of the gun should be held at least 4 to 10 inches (10-25 cm) away from the skull when fired. The use of hollow-point or soft-nosed bullets will increase brain tissue destruction and reduce the chance of ricochet." On larger animals: "Larger mature animals will require at least a .22 magnum hollow- or soft-point bullet or, preferably, a 9mm or .357 caliber bullet" [62]. The animals are shot in the head, but in a way that maximizes the splintering of the bullets. Ranchers are encouraged to haul animal carcasses to disposal sites, but on the open range far from such facilities, I suspect many animals are left where they die. Livestock carcasses are more likely than dead deer to occur in open terrain where condors can easily reach them.

Another consideration is that lead exposure may not be as critical to condor survival as is often implied. Meretsky et al. [63] stated that any condors having high levels of lead in their blood "are best considered mortalities" if not subjected to chelation therapy (chemical binding of the lead in the bird's system, so it can be more readily eliminated). However, and as noted above [64], this is an unsupportable statement:"It is not true, however, that all condors with high levels of lead in their tissues will necessarily die because they can eliminate lead from blood and some internal organs rather fast unless continually re-exposed" [65]. Many of the condors exposed to lead may have survived the encounter through their natural resilience.

None of this is meant to deny the fact of lead poisoning of condors, or its probable role in the decline of the species. Without knowing the source of the poison, the magnitude of its historical impact can only be guessed at.

Chapter Notes

37. Janssen, D. L., and M. P. Anderson. 1986. Lead poisoning in free-ranging California condors. Journal of the American Veterinary Medical Association 189(9):1115-1117.
Wiemeyer, S. N., J. M. Scott, M. P. Anderson, P. H. Bloom, and C. J. Stafford. 1988. Environmental contaminants in California condors. Journal of Wildlife Management 52(2):238-247.

38. Locke, L. N., G. E. Bagley, D. N. Frickie, and L. T. Young. 1969. Lead poisoning and aspergillosis in an Andean condor. Journal of the American Veterinary Medicine Association 155(7):1052-1056.

39. Wiemeyer, S. N., A. J. Krynitsky, and S. R. Wilbur. 1983. Environmental contaminants in tissues, foods, and feces of California condors. Pages 427-439 in: Wilbur, S. R., and J. A. Jackson, Vulture biology and management. Berkeley, California: University of California Press.

40. Hall, M., J. Grantham, R. Posey, and A. Mee. 2007. Lead exposure among reintroduced California condors in southern California. Pages 163-184 in: Mee, A., and L. S. Hall (editors), California condors in the 21st century. Series in Ornithology No. 2. Nuttall Ornithological Club and American Ornithologists' Union. Cambridge, Massachusetts.

41. Parish, C. N., W. R. Heinrich, and W. G. Hunt. 2007. Lead exposure, diagnosis, and treatment in California condors released in Arizona. Pages 97-108 in: Mee, A., and L. S. Hall (editors), California condors in the 21st century. Series in Ornithology No. 2. Nuttall Ornithological Club and American Ornithologists' Union. Cambridge, Massachusetts.

42. Church, M. E., R. Gwiazda, R. W. Risebrough, K. Sorenson, C. P. Chamberlain, S. Farry, W. Heinrich, B. A. Rideout, and D. R. Smith. 2006. Ammunition is the principal source of lead accumulated by California condors re-introduced to the wild. Environmental Science and Technology 40(19):6143-6150.
Hunt, W. G., W. Burnham, C. N. Parish, K. K. Burnham, B. Mutch, and J. L. Oaks. 2006. Bullet fragments in deer remains: implications for lead exposure in avian scavengers. Wildlife Society Bulletin 34(1)167-170.

43. Nothing in this discussion is intended to cast doubt on the reality of lead poisoning in California condors. My purpose throughout this book is to evaluate through time the contribution that various agents made to the near-extinction of the species. This has been difficult to do in the case of lead poisoning because the discovery very quickly became ammunition (of another sort) in the national campaign to reduce and eventually eliminate lead in the environment. This is undoubtedly a worthy cause, but the demands for immediate action effectively quelled scientific inquiry into the issue as it affected condors, and a number of key questions have gone unanswered.

44. Hundreds of newspaper, magazine and journal articles could be cited, but almost all arose from speculations of Noel and Helen Snyder, for example:
Page 206 in: Snyder, N. F. R., and H. A. Snyder. 1989. Biology and conservation of the California condor.

Pages 175-267 in: Power, D. M. Current ornithology, Volume 6. New York, New York: Plenum Press.

Page 252-253 in: Snyder, N., and H. Snyder. 2000. The California condor, a saga of natural history and conservation. San Diego, California: Academic Press.

45. Koford 1953 op. cit., page 55.

46. Miller, McMillan and McMillan 1965, op. cit., page 26.

47. Pages 24-27 in: Wilbur, S. R. 1978. The California condor, 1966-76: a look at its past and future. North American Fauna Number 72. Washington, D. C.: U. S. Fish and Wildlife Service.

48. Blong, B. 1954. A South Coast deer range. Los Angeles, California: Department of Fish and Game.
Taber, R. D., and R. F. Dasmann. 1958. The black-tailed deer in the chaparral. Game Bulletin Number 8. Sacramento, California: Department of Fish and Game.

49. Snyder and Snyder 2000 op. cit., page 152.

50. Meretsky, V. J., and N. F. R. Snyder. 1992. Range use and movements of California condors. Condor 94(2):313-335.

51. Snyder and Snyder 2000 op. cit., page 253.

52. Page 58 in: Fry, D. M., and J. R. Maurer. 2003. Assessment of lead contamination sources exposing California condors. Species Conservation and Recovery Program Report, 2003-02, California Department of Fish and Game. Sacramento, California.

53. Cited on page 10 in: Johnson, C. K., T. Vodovoz, W. M. Boyce, and J. A. K Mazet. 2007. Lead exposure in California condors and sentinel species in California. Report for the California Department of Fish and Game. Wildlife Health Center, University of California, Davis.

54. Personal communication, 28 January 2012, Grainger Hunt (The Peregrine Fund) to S. R. Wilbur: "Yes, the guys in Arizona have seen condors feeding on ungulate gut piles (and) there have been numerous radio fixes of condors at gut piles."

55. Fry and Maurer 2003, op. cit., page 58.

56. Hall et al. 2007, op. cit.
Sorenson, K. J., and L. J. Burnham. 2007. Lead concentrations in the blood of Big Sur California condors. Pages 185-195 in: Mee, A., and L. S. Hall (editors), California condors in the 21st century. Series in Ornithology No. 2. Nuttall Ornithological Club and American Ornithologists' Union. Cambridge, Massachusetts.

57. Fry and Maurer 2003, op. cit., page 32.

58. California Department of Fish and Game has compiled records by county of reported deer kill back to 1927: Mohr, R. C., and M. Parker. 2008. 2007 California deer kill report. Deer Management Program, Wildlife Programs Branch. Sacramento, California. Reports for subsequent years are also available. According to Craig Stowers, Deer Program Coordinator, reporting procedures have changed only in minor ways through the years (personal communication, 24 January 2012).

59. The Department of Fish and Game uses various weighted correction factors to convert reported deer kill (from their various surveys) to an estimate of the actual kill. The estimated kill is not shown by county in the Department's compiled reports, so these figures are my estimates.

60. Church et al. 2006, op. cit.

61. Anonymous. 1999. The emergency euthanasia of sheep and goats. Sacramento, California: California Department of Food and Agriculture.

62. Jensen, W., and J. Oltjen. 2007. Beef care practices. Davis, California: University of California Division of Agriculture and Natural Resources.

63. Meretsky, V. J., N. F. R. Snyder, S. R. Beissinger, D. A. Clendenen, and J. W. Wiley. 2000. Demography of the California condor: implications for reestablishment. Conservation Biology 14(4):957-967.

64. Fry and Maurer 2003 op. cit., page 32.

65. Cade, T. 2007. Exposure of California condors to lead from spent ammunition. Journal of Wildlife Management 71(7):2125-2133.


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