I read regularly - including in reports from the government and private offices currently engaged in California condor reintroduction - that nobody knows why the condor population declined to near extinction. That is far from true. With the exception of still needing to speculate and hypothesize about why condors disappeared from the northern extremities of their range, the record is pretty clear. Here's what happened.
[The following was originally published as a chapter in: "Nine Feet from Tip to Tip: the California Condor through History." (Gresham, Oregon: Symbios Books, 2012). If you would like a free copy (PDF) of the entire book, send me an e-mail.]
In the preceding chapters[of "Nine Feet.."], I surveyed the history of California condors from before human presence until the early 1980s, when management emphasis changed from preserving the remaining wild population to a captive breeding program. The presentation was meant to entertain and inform, and also to correct or further analyze some of the popular condor stories that had developed through the years. Also, I planned the chapters in the book to lay the groundwork for asking - and to the extent possible, answering - the question: why did the California condor population decline to the point at which extinction was almost certain?
Many different opinions about the causes of the condors' decline have been expressed over time. Varying ideas about history are inevitable; those who actually live the history seldom leave behind the records that would be most useful to those who later try to interpret it. With the condor, we have - at best - a very fragmented record to work with. A further complication arises because most writers of the 20th and 21st centuries haven't known that the popular record of condor history has been badly tainted since the 1850s. Few recognize the name of Alexander Taylor today, but few books and articles written about condors in the last 150 years have not been influenced by Taylor's imagination and exaggeration (Chapter 8). No condor researchers or historians other than myself, Harry Harris, and Carl Koford have spent any significant amount of time looking at primary and secondary references. New books may have new research findings, but the authors almost always refer back to earlier books for their historical information.
For the following analysis, I reviewed some 3,000 sources. Two-thirds of them specifically mention condors; the others provided information on historical conditions within the condor range, or supplementary data to help interpret the condor material. The types of condor records (with the approximate percentage of the total shown for each) were: published books (15%), articles in serial publications (45%), newspapers (15%), library and museum archival records (20%), and various government documents and unpublished matter (5%). Chronologically, the records date from: before 1850, 2%; 1850-1900, 25%; 1901-1930, 25%; 1931-1960, 15%; 1961-1980, 20%; and after 1980, 13%.
From the compiled record, I identified specific agents known or suspected to have impacted the condor population, and have looked at their potential effects both chronologically and geographically. I considered three general circumstances that might have had a significant effect on the condors' ability to maintain a viable population over time: major changes in habitat, making areas unable to support condors; changes in productivity great enough to have caused an unnatural decline in numbers; and excessive mortality.
Habitat Change:
There is no evidence (and little likelihood) that habitat loss or degradation caused significant changes in the condor population. Certainly, useable acreage - particularly of feeding habitat - has been lost over time, but I don't think there is any region that was occupied in 1800 that could not support condors today. Even in Baja California, Mexico - where in the past I have questioned whether food supply was adequate to support a condor population [1] - recently released condors have been regularly finding natural food (mule deer, bighorn sheep, burro, cattle, horses) to supplement that artificially provided to them [2].
Depressed Productivity:
Changes in productivity - either within the population generally, or for individual birds - does not appear to have been a significant problem for condors. Nevertheless, there are several ways the species could have been affected: by loss of genetic diversity, from the effects of the chemical DDT, or as a result of group limitations brought about by fewer condors living in a region.
Genetics - Reduction in genetic diversity is a potential problem with any declining species, and some loss has occurred over time with the captive flocks of California condors [3]. Nevertheless, the current population of nearly 400 condors are all derived from six breeding pairs, with little or no evidence of genetic decline. One would think that in the past, with many more breeding pairs and greater geographic distribution, genetic problems would have been less significant than currently.
ddt - Beginning about 1944, massive amounts of the organochlorine DDT were applied to kill insects in the United States and around the world. Peak use in the United States occurred about 1959, but continued at high levels until DDT was banned in the U. S. in 1972. One result of this pesticide use was "thin eggshell syndrome," in which DDE - the principal metabolite of DDT - interfered with calcium production in birds, causing extreme production failure in some species due to their laying fragile thin-shelled eggs [4]. Eggshell thinning was most strongly associated with birds that fed heavily on fish or other birds (brown pelicans, bald eagles, ospreys, peregrine falcons). Therefore, it came as a surprise that comparisons we did between condor eggshells from before DDT use and those collected 1964-1969 showed the DDT-era samples to be 32% thinner than those from before 1944. This was quite high compared to most other species that had been studied; average thinning of more than about 18% has been associated with population declines. The deterioration of the shell layers in the thin condor eggs was spectacularly evident through the electron microscope. Also, we found significant residues of DDE in the more recent eggshells [5].
Historically, condor egg breakage occurred regularly; about 10% of eggs known to have been taken by collectors were reportedly found punctured or otherwise damaged at the nest site [6]. If it was natural for 25-pound birds laying eggs on hard rock floors to sometimes damage the shells, it seems inevitable that DDE-thinned eggshells would be even more vulnerable.
Shell thinning contributing to egg breakage is the most obvious sign of DDE influence on avian productivity, but disruption of normal breeding behavior is also possible. Among changes noted in various species have been decreases in nest attentiveness, lessening of courtship activities, and changes in expected nest defense [7]. There is no evidence that DDE contamination disrupted condor behavior, and only one condor egg was found that was so thin-shelled that it crushed immediately after laying. Nevertheless, considering the potential for egg breakage, and the possibility of aberrant behavior by breeding birds with high DDE levels, it seems to me likely that DDE had some role in the reduced productivity observed in the 1960s and 1970s.
Population characteristics - Observations made by me and by Fred Sibley in the 1960s and 1970s suggested that - considering the size of the condor population - average annual production was only about half of what seemed possible [8]. At the time, I thought that decreased productivity was principally due to less reproductive activity rather than lack of nest success [9]. As noted above, I may have been wrong in not considering DDE contamination at least a part of the problem. With or without chemicals in the equation, as the numbers of condors decreased, chances of successful pair formation could have been reduced by uneven sex ratios, disparate age structure, and varying sexual experience. With a natural tenacity by individuals to certain nesting, roosting and feeding sites, potential to meet prospective mates would have been reduced by each fragmenting of the population. In general, the larger the reservoir of condors, the better the chances would have been for pair formation.
If decreased productivity was a significant factor in the near demise of the California condor, the effects would have been greatest in the last 20-25 years, when the combined impacts of DDE and reduced population size would have been most likely. It is possible that, even in the late 19th century, some localized groups of condors could not sustain themselves as other factors isolated them from former outside recruitment. Whatever productivity issues occurred, I think their impact was minor compared to the measurable toll of human-related mortality.
Excessive mortality:
I was able to document 458 instances of California condor mortality occurring between 1602 and 1985, 450 of them in the 190 years after 1793. An average of approximately two condors lost per year does not sound particularly significant, but there is more to the story. For example:
1. Because of the condors' low reproductive potential, population stability required long life for individual birds, with almost all mortality the result of old age and "natural" deaths (accidents, diseases). Even minor changes in the balance between birth and death would be reflected in the species to a much greater degree than in most birds.
2. The record of human-related mortality is almost certainly far from complete. After what seemed like a fairly exhaustive search between 1966 and 1978, Fred Sibley and I compiled a list of some 300 deaths [10]. The 150 records added since then were made possible by today's sophisticated internet search engines and by the continuing digitization of historical newspapers, allowing access to information previously unavailable to the average researcher. Even now, many California newspapers published between 1850 and 1950 are not readily searchable. A number of these were published in communities in the heart of "condor country," and it would be surprising if more records are not eventually found in them. Of course, even if all the documented losses were discovered, they would still constitute some unknown (but I suspect, small) portion of the actual number of human-related mortalities.
3. Of the mortalities documented, 334 (74%) occurred in only 30 years, 1880-1909. Of these, approximately 90 (over 25%) were from just two parts of the total condor range, the Monterey County area and the San Diego County area. Even without knowing how recorded losses compare to actual mortality, it is clear that certain segments of the condor population suffered major upsets to their natural gain:loss balance during that 30-year period.
* * *
Causes of mortality - Of the 458 mortalities documented, 14 were "natural" losses - deaths that would have occurred with or without human presence (disease, collision with cliffs). The reasons for another 88 losses could not be positively ascertained from the information available [11]. The remaining 356 records have been divided between eight categories.
Killing for sport or curiosity - Forty percent of the records were of condors killed merely because they were big and interesting. Most were shot, but six were lassoed and a few were killed by other means. Killing for sport was documented in every decade through the 1970s, with over 50 percent recorded between 1880 and 1909. This is probably a true representation of when sport killing reached its peak, but it is also the period during which - with no stigma attached to killing a condor, and with newspapers actively soliciting unusual local stories - such events were most likely to be reported. By 1900, there was a decided change in public sentiment about killing wildlife, and groups such as local (and eventually, national) Audubon societies were pressing for laws against unregulated killing. Opinions favoring "birds of prey" were slower to develop than for some other avian groups, but the number of reported killings fell sharply after 1910.
I searched on one popular historic newspapers website for the phrase "from tip to tip" (a common measure of a bird's wingspan or a mammal's length). Among the species interesting enough for their "tip to tip" measurement to warrant mention in the news were eagles, hawks, owls, herons, pelicans, swans, mountain lions, and of course, condors. From 1800 to 1850, I found some 300 "tip to tip" citations. The number of records increased every decade until 1901-1910, when the number exceeded 3,000. After 1910 - even though the number of digitized, searchable newspapers increased with each decade - the number of "tip to tip" references (for all wildlife) in the 1930s was down to around 500 nationwide, and only 300 in the 1940s. Some of the change undoubtedly reflects a real decrease in the number of large birds shot for sport or curiosity. Some unknown portion is a result of more wildlife law enforcement and more public concern about killing "birds of prey," both of which made it much less desirable to openly praise one's shooting prowess.
The first prosecution for killing a condor occurred in 1909 [12]. This undoubtedly contributed to a decrease in reporting shooting incidents, if not necessarily to an actual decrease in shooting. Both Carl Koford in the 1930s and 1940s [13], and the McMillan brothers in the mid-1960s [14], thought that shooting was still taking a significant toll. Only a few certain condor deaths were recorded, but both studies documented considerable shooting at large soaring birds within the condor range.
Killing for private collections - Close behind sport killing as a cause of mortality was the acquiring of condor specimens for private collections (31% of the total). In fact, some of this number may actually have begun as killings for sport, after which the hunters found there was a market for selling their trophies. In most cases, the records of these condors indicated they went more or less directly from the hunter to a taxidermist, a known private collection, or to a natural history supply house that sold specimens. As discussed in Chapter 15, many of these specimens eventually were acquired by public institutions, and a number of the collectors later became curators of public museums. Initially, however, these were condors taken by or for hobbyists.
Only a few bird collectors were operating before the 1870s, and only John Gurney in England had more than one or two California condors (Chapter 8). As collection laws tightened in the early 1900s, legal taking of condors ceased, and only a few are known to have been acquired after 1910. Like sport killing, hobby collecting was at its peak between 1880 and 1910 (over 86% of the specimens taken). Unlike sport killing, which continued opportunistically and surreptitiously in ensuing years at unknown levels, hobby collecting ended. Many of the specimens taken by hobbyists are still in existence, and the record of this particular impact is probably nearly complete.
Collecting for museums and scientific investigation - I consider only 55 condor mortalities (16%) attributable to scientific study or specific acquisition for public museums. The record appears to be nearly complete, and no more than 10 specimens were taken for this purpose in any decade. Even though considerably less significant than sport killing or hobby collecting, scientific collecting was one more drain on the condor population. Perhaps most important is that 20 percent of losses in this category came after 1910, when there was no question that the species was in trouble (Chapter 15).
Live capture for zoos and menageries - Beginning with at least two condors in Grizzly Adams' live animal show in the late 1850s, 16 condors (5%) are known to have been taken into captivity for display purposes (Chapter 12). Usually only one or two were captured in any decade, although there were six taken 1900-1909. Most of the captive condors were taken from nests, leaving the adult birds to produce additional eggs. While adding to the general disruption occurring in the late 19th and early 20th centuries, the taking of these nestlings would have had little direct impact on the condor population.
Losses associated with predator and rodent control - Nine accidental deaths (2%) were attributable to animal control activities: five from ingestion of poison (probably strychnine), three from being caught in leg-hold traps, and one possibly from cyanide gas released by an M-44 "coyote getter" [15]. Only one of the incidents occurred before 1880, by which time it was being regularly reported that poisoning was the principal cause of condor deaths. As explained previously (Chapter 11), both chronologically and geographically, it is almost impossible for strychnine to have been a major killer of condors in the 19th century. A much better chance for poison to have taken a significant toll would have occurred after 1915, when the U. S. Bureau of Biological Survey (BBS) began establishing formal predator control programs in the West. "By 1917, the BBS had established districts throughout the US and initiated cooperative funding with states and counties... In time, the field men worked in both predator and rodent control. After 1917, this type of activity ramped way up" [16]. Because it was no longer fashionable to publicize the death of big birds - and because animal control already received enough adverse publicity without adding condor deaths - the chances of a fatality being reported were probably less than in earlier times.
Killing allegedly to protect livestock - Eight condor fatalities (2%) occurred because the shooters reportedly believed that condors were attacking their calves, lambs, or hogs. In a few cases, there may have been a real fear of depredations; for example, one herder admitted he mistakenly shot a condor because he thought it was an eagle. In most instances, I'm inclined to think that herd protection was a stated excuse for what were really shootings for sport. Granted that many ranchers were wary of any large soaring bird around their flocks, the stories told about the shootings were sometimes so outrageous they seem like after-the-fact justifications: e.g., the condor was flying off with a calf when killed; it had killed 30 pigs before being shot; etc.
Accidental human-related deaths - In contrast to such natural condor losses as from disease, hailstones, or flying into canyon walls, ten deaths (3%) would not have occurred without a human element. Typical were deaths caused by flying into power lines, or into other man-made objects. Also in this category were three cases of lead poisoning, the result of bullet fragments in food eaten by condors. Obviously, the opportunities for such losses would have increased with each succeeding generation, as human presence in condor habitat grew. Even so, with the exception of lead poisoning, the likelihood of such deaths was relatively low. Deaths from lead ingestion could have occurred regularly without being detected (Chapter 23).
Killing for quills - The often-told story of condors being killed so that miners would have receptacles in which to store their gold is just that: a story (Chapter 9). There are no specimens, or even reliable narratives, that suggest the practice occurred in California. There are four records (1%) from Baja California, Mexico, in which quill collecting was reported to have been the objective for killing the birds. All four accounts are suspect in some way (Chapter 9); lacking proof one way or the other, I've included them here as a possible minor source of condor mortality.
* * *
With the exception of localized killing of condors by Native Americans - apparently of regular occurrence only in the lower Sacramento Valley and adjacent hills, and mostly before 1850 (Chapter 2) - almost all human-related losses of condors can be placed in one of the categories above. Every non-natural loss had a greater effect on the condor population than would have been the case with most other species, so no factor can be considered neutral. As the range of the species contracted and the numbers of condors decreased, the effect of any loss for any reason would have been magnified. Nevertheless, the only factor that spans all generations and locations was killing for sport. Combined with hobby and institutional collecting between 1880 and 1910, the losses were great enough to extirpate condors in some areas and to seriously depress their survival potential throughout their range.
Old stories die hard, particularly if they are romantic (Indians sacrificing condors, miners carrying gold in condor quills) or if they support a particular belief or point of view (poisoning predatory mammals must have poisoned many condors, also). When presented in books that appear authoritative, it is often because the writers have done inadequate historical research, and have just repeated readily available information. Sometimes, writers resort to acknowledging that there is little support for a belief they favor, but suggest that "we simply don't know enough to make a judgment" [17]. Framed as "the absence of evidence is not evidence of absence," or "absence of proof is not proof of absence," credit for the quote is usually given to the poet William Cowper, who allegedly presented the argument to explain his belief in God [18]. Used for everything from supporting the potential existence of extraterrestrial life [19], discussing the archaeological excavation of London [20], to lampooning religious arguments by introducing the Flying Spaghetti Monster into the debate about teaching creationism and evolution in schools [21], the argument does have some logical validity. For example, lead poisoning appears as a minor source of condor mortality if only actual records through 1986 are considered. However, based on recent findings, it appears possible (likely?) that death from ingesting lead bullet fragments has been a long-term, potentially serious problem for the condor population. The historical "absence of evidence" is the result of such deaths being inconspicuous, and of our not having the ability to monitor that aspect of condor survival until the 1980s when condors could be trapped and blood samples analyzed (Chapter 23).
The lead poisoning example notwithstanding, scientific investigation - like the law - depends on evidence. Without some strong support, invoking the "absence of evidence" mantra "might be used to deflect criticism away from one's failure to provide such positive justification for a claim one has made. The requirement of fulfilling the burden of proof for a claim one has made is a fundamental principle of argument..." [22]. A flea and elephant comparison illustrates: "If someone were to assert that there is an elephant on the quad, then the failure to observe an elephant there would be good reason to think that there is no elephant there. But if someone were to assert that there is a flea on the quad, then one's failure to observe it there would not constitute good evidence that there is no flea on the quad. The salient difference between these two cases is that in the one, but not in the other, we should expect to see some evidence of the entity if in fact it existed. Thus the absence of evidence is evidence of absence only in cases in which, were the postulated entity to exist, we should expect to have some evidence of its existence" [23].
In Chapter 11, I showed that the original story of major condor losses to strychnine poisoning was erroneous; that later authors embellished the story with no additional information; that geographically and chronologically the use of strychnine does not match with the decrease in condors; and that regular deaths of condors in the 19th century would have been documented. In Chapter 9, I deconstructed the tale of condor quills and gold dust to show that there is no basis for treating feather harvesting as significant in the decline of the condor population. The story of Indians sacrificing condors (Chapter 2) stems from incorrect interpretation of early records of eagles; completely without merit is the recently-stated belief that Indians may have been responsible for "a potential annual take on the order of 700 condors" [24]. All three - strychnine, condor quills, and Native Americans - have been treated as "elephants" in the near extinction of the California condor; there is not even enough support to treat them as "fleas." Strychnine use and sport killing after 1910 - when it was no longer wise to talk about condor deaths - may well qualify as "fleas," and lead poisoning might qualify as a significant infestation of that bug. The "absence of evidence" argument may be valid in those three cases. As for "elephants" on the condors' "quad," there were only two: sport killing, and specimen collecting.
Chapter Notes
1. Wilbur, S. R., and L. F. Kiff. 1980. The California condor in Baja California, Mexico. American Birds 34(6):856-859.
2. Wallace, M. P., M. Clark, J. Vargas, and M. C. Porras. 2007. Release of puppet-reared California condors in Baja California, Mexico: evaluation of a modified rearing technique. Pages 227-242 in: Mee, A., and L. S. Hall (editors). California condors in the 21st century. Series in Ornithology No. 2. Nuttall Ornithological Club & American Ornithologists' Union. Cambridge, Massachusetts, and Washington, D. C.
3. Adams, M. S., and F. X. Villablanca. 2007. Consequences of a genetic bottleneck in California condors: a mitochondrial DNA perspective. Pages 35-55 in: Mee, A., and L. S. Hall (editors), California condors in the 21st century. Series in Ornithology No. 2. Cambridge, Massachusetts, and Washington, D. C.: Nuttall Ornithological Club & American Ornithologists' Union.
4. Cooke, A. S. 1973. Shell thinning in avian eggs by environmental pollutants. Environmental Pollution 4(1):85-152.
Stickel, W. H. 1975. Some effects of pollutants in terrestrial ecosystems. Pages 25-74 in: McIntyre, A. D., and C. F. Mills (editors), Ecological toxicology research. New York, New York: Plenum Publications.
5. Kiff, L. F., D. B. Peakall, and S. R. Wilbur. 1979. Recent changes in California condor eggshells. Condor 81(2): 166-172.
Kiff, L. F. 1989. DDE and the California condor Gymnogyps californianus: the end of a story? Pages 477-480 in: Meyburg, B. U., and R. D. Chancellor (editors), Raptors in the modern world. Proceedings of the 3rd World Conference on Birds of Prey and Owls.
6. Kiff 1989, op. cit.
7. Peakall, D. B. 1996. Disrupted patterns of behavior in natural populations as an index of ecotoxicity. Environmental Health Perspectives 104 (Supplement 2):331-335.
Haegele, M. E., and R. H. Hudson. 1977. Reduction in courtship behavior induced by DDE in male ringed turtle doves. Wilson Bulletin 89(4):593-601.
8. With no way to positively identify individual condors or to track pairs over time, my "life tables" were developed from population census estimates, direct observations of nesting activity, determination of the success of known nests, and changes in the percentages of immature-plumaged condors in the population. While admittedly rough, my conclusions were deemed reasonable by several population modelers.
9. Pages 22-24 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.
10. Wilbur 1978, op. cit., pages 71-88.
11. It appears that most of these losses were the result of either random shooting or purposeful acquisition of specimens for private collectors. There isn't quite enough information on these deaths to confidently assign causes of death.
12. Anonymous. 1909. Condor without mate. Hunter who shot great rare bird is found guilty and will be sentenced tomorrow. Los Angeles (California) Times, 24 January 1909.
13. Page 129 in: Koford, C. B. 1953. The California condor. Research Report Number 4. New York, New York: National Audubon Society.
14. Pages 29-36 in: Miller, A. H., I. I. McMillan, and E. McMillan. 1965. The current status and welfare of the California condor. Research Report Number 6. New York, New York: National Audubon Society.
15. Laboratory tests after initial evaluation raise doubts of cyanide from an "M-44" being the cause of death: Wiemeyer, S. N., E. F. Hill, et al. 1986. Acute oral toxicity of sodium cyanide in birds. Journal of Wildlife Diseases 22(4):538-546.
16. Personal communication, 23 March 2012, from Nancy Freeman, Archivist, National Wildlife Research Center (Fort Collins, Colorado).
17. Page 3 in: Walton, D. N. 1996. Arguments from ignorance. University Park, Pennsylvania: Pennsylvania State University Press.
18. There must be thousands of sentences written that contain the phrase "as Cowper said;" however, no one seems to know where the "quote" originated!
19. "All we can safely conclude is that intelligent life has evolved at least once. Even if it existed elsewhere, we might not recognize it. Intelligent extraterrestrials may lead contemplative lives, and have no motive for signaling their presence to us: absence of evidence cannot be evidence of absence." Page 23 in: Rees, M. J. 1997. Before the beginning: our universe and others. Reading, Massachusetts: Addison-Wesley.
20. Regarding "the ever-intriguing question of post-Roman London; and on this, even while remembering the important fact that absence of evidence is not identical with evidence of absence, it does at least seem significant that (so many additional excavations) have still produced no positive evidence of life continuing through the late fifth and early sixth centuries." Burn, A. R. 1969. Book review: The excavation of Roman and Mediaeval London, by W. F. Grimes. The Classical Review, New Series, 19(2):229-232.
21. Henderson, B. 2006. The gospel of the Flying Spaghetti Monster. New York, New York: Villard Publishing.
22. Walton 1996 op. cit., page 2.
23. Evans, C. S., and M. Westphal. 2003. Religious epistemology. Pages 155-170 in: J. P. Moreland and W. L. Craig. Philosophical foundations for a Christian worldview. Downers Grove, Illinois: Inter Varsity Press.
24. Page 44 in: Snyder, N. F. R., and H. Snyder. 2000. The California condor, a saga of natural history and conservation. San Diego, California: Academic Press.
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