The most significant factor in the near extinction of the Californian Condor was lead poisoning through exposure to hunting ammunition.
What the science says
Although condor numbers had been declining gradually for some time, sharper declines led numbers to crash down to only 22 individuals in the wild in 1982. This was caused by lead poisoning from exposure to ammunition in their carrion food. As a scavenger feeding on carcasses shot with lead, fragments of lead ammunition accumulated in condors, and many were found to have lead poisoning in the 1970s and 80s. Tests on the blood of some of these birds confirmed lead ammunition as the source of exposure. When numbers became critically low, the remaining individuals were captured, to establish a breeding and re-release programme. After their release, ongoing lead exposure has affected these birds too, necessitating very high levels of ongoing management, maintenance and care to the extent that the population could not be viable without such intervention. Lead ammunition is now illegal in California, and Arizonan authorities have worked hard to reduce lead ammunition use by hunters.
This statement was made in an article which ran in the Observer on Sunday 28th March 2021.
It once soared from British Columbia to Mexico, but habitat loss, overhunting and most significantly poisoning by hunting ammunition drove the birds to near extinction.
The fuller picture
Californian condor numbers were gradually falling through the 19th and into the early 20th century for many reasons, including habitat loss and direct persecution. As a scavenging species, Californian condors feed exclusively on carrion and historically the species is thought to have fed often on marine mammal carcasses, but in recent centuries their primary food source switched to those associated with human activity such as livestock, hunted carcasses or the gut piles left when shot animals were gralloched in the field. This switch opened up the route for exposure to both poisoned carcasses (left out by early settlers to remove predators) and lead ammunition.
When lead cored rifle bullets hit an animal such as a deer they spread to a mushroom shape on impact, and fine fragments break off and disperse through the carcass – leaving many small, sometimes microscopic, pieces of lead throughout. The carcass or any remains which are left on the ground can therefore be a source of lead exposure for any animal that scavenges it. The approximate dose of lead thought to be lethal to the Californian condor is 33-65 mg (less than 1% of the standard 9700mg rifle bullet), so one carcass can contain enough lead fragments to kill many adult condors1. There is strong evidence and a general scientific consensus that by 1982, when numbers had crashed to only 22 individuals remaining in the wild, exposure to lead from ammunition was the major cause of the decline in condor numbers1–3. Of the last 15 birds to die in the wild at this time, four were recovered for analysis and of these, three had died from separate lead poisoning incidents3,4.
Lead ammunition exposure was not only the predominant reason for severe declines through the mid-20th century leading up to the near-extinction, but it also remained an ongoing problem for both condors that were released from the conservation programme and those which have hatched in the wild since then5,6.
Measuring the level of lead in condor blood samples during the early 2000s confirmed this, showing that many individuals had very high blood lead concentrations. The fact that the levels were high didn’t necessarily mean lead ammunition was the source, so to determine the route of exposure, the scientists analysed the type of lead using isotope ratios. This allows the source of the lead to be identified, as ammunition lead has a different isotope ratio to that from background exposure ie. in soil, food etc. This work showed that the raised levels of lead in condor blood samples matched the profile from lead ammunition7.
Another study published in 2014 once again measured lead levels and isotope ratios in blood samples from captive-bred condors and those that had been released. The results showed that the levels of lead in pre-release birds were low, and that these rose to be almost ten times higher after release. The isotope ratio measurements changed from those matching normal environmental exposure before release, to matching ammunition lead afterwards8.
The following quotes come from a report prepared by the American Ornithologists’ Union in 2008 to review the Californian condor conservation programme1:
“Lead poisoning resulting from ingestion of spent ammunition in carcasses is so severe and chronic a problem at all release sites that the program is unified in the belief that condor recovery cannot be achieved so long as such lead exposure continues. Condors almost certainly would not survive in the wild were they not regularly trapped, tested and treated for lead. Several individuals have been saved from death from lead poisoning multiple times…
… Feeding, trapping and chelation treatment reduce deaths from ingestion of lead, but the impacts of sublethal exposure to lead are as yet unknown. Effects on behaviour and demography are likely, given the current levels of exposure.”
“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”.
However, lead exposure is not the only ongoing problem faced by the released or newly wild bred Californian condors, with the following from the same report:
“It is likely that fledging success would be reduced to zero again if chicks were not vaccinated for West Nile virus, examined monthly for ingestion of microtrash (i.e., small bits of refuse of human origin including items such as rags, nuts, bolts, washers, plastic, bottle caps, chunks of pipe, spent cartridges, and pieces of copper wire) and treated on site by veterinarians and field biologists”.
Wild condors face many threats, including exposure to pollutants in the environment9 and infectious diseases – a problem which may have been exacerbated by their near-extinction. Although numbers are rising, the period of very low numbers means that all the individuals now alive are descended from only a handful in the 1980s/1990s. This crash followed by recovery has reduced their genetic variation10, the sort of bottleneck event that can leave a recovered population vulnerable. Limited diversity in any population can be a problem, such as was seen in African cheetah populations, for example meaning that more individuals might be susceptible to particular diseases11.
The conservation programme is considered to be a success, with the population up to over 500 individual birds and wild condors now seen again in the skies of southwest America. However, the issue of exposure to and poisoning by lead ammunition continues to be a serious problem, with sustained and considerable intervention still required to protect the birds.
Current lead ammunition usage
The state of California began the journey to make hunting with lead ammunition illegal in 2008, when regulations on the use of lead projectiles for big game and nongame hunting were implemented throughout the condor’s range. This was broadened in 2013, when further legislation came into place restricting the use of lead ammunition in some areas of the condor’s territory, and the process was completed in June 2019, when a complete ban on hunting with lead ammunition was implemented across the state. There is limited scientific evidence so far on the effect of the reduction and then ban on lead in California on condor populations, but a study looking at lead exposure over fifteen years up until 2011 found little effect of the initial restrictions introduced in 200812. The authors suggest that this was likely to be the result of some non-compliance with the rules, poaching, and activities not covered by the regulations such as shooting feral pigs or euthanising livestock. However, there are promising signs from elsewhere that a switch away from lead ammunition can be effective, if adhered to.
Californian condors are also found in northern Arizona, southern Utah and south-eastern Nevada. In Arizona, the Game and Fish department introduced a public education programme in 2003 to encourage hunters to use non-lead ammunition. By 2006 there was a 50-60% voluntary participation, which was increased to over 80% compliance in 2007. This seems to have been effective as, during the 2007 season, lead exposure in condors was lower and no lead toxicity fatalities occurred13. The impact of the 2019 regulations in California may take some time to be felt, but there is the potential for a real improvement.
Exposure to lead from hunting ammunition was the main factor driving Californian condors to near extinction in the late 1980s. The subsequent conservation programme which focussed on capture and re-release to save the species has been successful, but ongoing use of lead ammunition at that time meant that both re-released and wild condors continued to suffer from lead exposure – often requiring veterinary treatment to reduce their blood lead levels2. It is hoped that recent voluntary moves away from lead in some states and legislation to ban lead ammunition in others will be effective in reducing exposure and improving the health of condors.
However, this problem is not confined to Californian condors and appears to be much more widespread. A 2019 review found that lead contamination was a problem in every area of the world where condors or vultures are found, with most individual birds having raised blood lead levels. Although it is not often confirmed by studies such as we have seen with the condor, the most reported source is lead ammunition14.
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2. Walters, JR, Derrickson, SR, Michael Fry, D, Haig, SM, Marzluff, JM & Wunderle, JM. (2010) Status of the California Condor ( Gymnogyps californianus ) and Efforts to Achieve Its Recovery . The Auk, 127:
3. Meretsky, VJ, Snyder, NFR, Beissinger, SR, Clendenen, DA & Wiley, JW. (2000) Demography of the California Condor: Implications for reestablishment. Conservation Biology 14: 957–967
4. Janssen, DL, Oosterhuis, JE, Allen, JL, Anderson, MP, Kelts, DG & Wiemeyer, SN. (1986) Lead poisoning in free-ranging California Condors. Journal of the American Veterinary Medicine Association, 155: 1052–1056
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8. Church, ME, Gwiazda, R, Risebrough, RW, Sorenson, K, Chamberlain, CP, Farry, S, Heinrich, W, Rideout, BA & Smith, DR. (2006) Ammunition is the principal source of lead accumulated by California Condors re-introduced to the wild. Environmental Science and Technology, 40: 6143–6150
9. Burnett, LJ, Sorenson, KJ, Brandt, J, Sandhaus, EA, Ciani, D, Clark, M, David, C, Theule, J, Kasielke, S & Risebrough, RW. (2013) Eggshell thinning and depressed hatching success of California condors reintroduced to Central California. Condor, 115:
10. D’Elia, J, Haig, SM, Mullins, TD & Miller, MP. (2016) Ancient DNA reveals substantial genetic diversity in the California Condor (Gymnogyps californianus) prior to a population bottleneck. Condor, 118:
11. Pacheco, MA, Parish, CN, Hauck, TJ, Aguilar, RF & Escalante, AA. (2020) The endangered California Condor (Gymnogyps californianus) population is exposed to local haemosporidian parasites. Scientific Reports, 10:
12. Kelly, TR, Grantham, J, George, D, Welch, A, Brandt, J, Burnett, LJ, Sorenson, KJ, Johnson, M, Poppenga, R, Moen, D, Rasico, J, Rivers, JW, Battistone, C & Johnson, CK. (2014) Spatiotemporal Patterns and Risk Factors for Lead Exposure in Endangered California Condors during 15 Years of Reintroduction. Conservation Biology, 28:
13. Sieg, R, Sullivan, KA & Parish, CN. (2009). Voluntary lead reduction efforts within the northern Arizona range of the California Condor.
14. Plaza, PI & Lambertucci, SA. (2019) What do we know about lead contamination in wild vultures and condors? A review of decades of research. Science of the Total Environment 654: