Conserving the California condors

This is article no. 2 in a series on animal conservation. Next article: Beavers are back in Britain (coming soon). Previous article: The cost of coats: celebrating 55 years of vicuna conservation.

California condors are critically endangered birds living on the west coast of North America. Their population decline was first reported in 1953, and they were nearly extinct by 1987. Since then, a captive breeding and reintroduction program has saved the species in the face of multiple human threats. This article will describe some of those threats and available measures to mitigate them.

Why California condors became endangered

Lead poisoning was the main cause of California condor mortality in the late 20th century. Like vultures, California condors eat dead mammals. When these mammals were shot dead with lead bullets, condors ingested fragments of the bullets, and the lead poisoned their bloodstream. Multiple condors feeding on the same carcass got poisoned, which could be why the population crashed so badly.

Today, lead poisoning is the biggest, but not the only, threat to California condor survival (Figure 1). The birds used to be hunted for museums and private collections in the early 20th century, but nowadays, any shootings are accidental. A bigger concern, and the second-most common human-related cause of mortality, is condors colliding with utility poles and power lines. The third-most common is fires: a 2015 study found that every recent wildfire in California has coincided with at least one condor death. Climate change will make these fires more frequent and severe. These threats mainly apply to inland California condors - halogenated organic compound (HOC) pollution is an issue for coastal birds. When coastal condors eat marine mammals contaminated with HOCs, the compounds disrupt their reproductive system and thin their eggshells. In short, humans have created a hostile environment for California condors.

Successful captive breeding and population recovery

Despite these threats, captive breeding has grown the California condor population over 18-fold (Figure 2). In 1987, all remaining wild condors were captured and bred, with juveniles released to the wild from 1992 onwards. Reintroduced birds are monitored regularly, and poisoned birds are treated with chelation therapy - where a drug binds to lead in the bloodstream and takes it to the kidneys to be filtered out. Since 1995, power line collisions have been avoided by giving juveniles behavioural training before reintroduction. Because of these measures, the California condor mortality rate in the wild decreased from 37.2% in 1992-1994 to 5.4% in 2001-2011.

Challenges of conserving California condors

Although captive breeding has saved the California condor population, it has also altered behaviours. The original condors stay with one mate longer than reintroduced condors, which may form polygamous relationships. Scientists think that spending so much time with non-family members in captivity has made juveniles promiscuous when reintroduced. Captive bred condors have also gotten used to being fed by people - so they approach people more often, spend longer in areas of human activity, and forage over a smaller area than the original condors. Moreover, condors in southern California were spotted feeding their chicks human litter. These behavioural changes mean the wild California condor population is not self-sustaining.

The wild population is also not self-sustaining because condors are still being poisoned (Figure 3). Banning lead bullets is the most effective way to guarantee population growth, but enforcing it has been challenging. Non-toxic alternative bullets like copper cannot find popularity. For population growth, every adult California condor killed is estimated to be worth 2-3 reintroduced juveniles. This is because released juveniles are more vulnerable and take years to reach breeding age. Therefore, American conservationists must keep pressuring authorities to reduce threats to adult California condors. 

Conclusion

Pollution, urbanisation, and climate change have made it hard for the California condor population to recover from decades of lead poisoning. Long generation times and behavioural changes mean captive breeding is the species’ only hope of survival. Perhaps humans are the ones who need to change their behaviour - not feeding California condors and switching to copper bullets would allow these majestic birds to keep roaming the skies. 

Written by Simran Patel

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REFERENCES

Bakker, V.J. et al. (2024) Practical models to guide the transition of California condors from a conservation-reliant to a self-sustaining species. Biological Conservation. 291: 110447. Available from: https://www.sciencedirect.com/science/article/pii/S0006320724000089 (Accessed 19th September 2024).

D’Elia, J., Haig, S.M., Mullins, T.D. & Miller, M.P. (2016) Ancient DNA reveals substantial genetic diversity in the California Condor (Gymnogyps californianus) prior to a population bottleneck. The Condor. 118 (4): 703–714. Available from: https://doi.org/10.1650/CONDOR-16-35.1 (Accessed 28th September 2024).

Finkelstein, M.E. et al. (2023) California condor poisoned by lead, not copper, when both are ingested: A case study. Wildlife Society Bulletin. 47 (3): e1485. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1002/wsb.1485 (Accessed 28th September 2024).

Kelly, T.R. et al. (2015) Two decades of cumulative impacts to survivorship of endangered California condors in California. Biological Conservation. 191: 391–399. Available from: https://www.sciencedirect.com/science/article/pii/S0006320715300173 (Accessed 28th September 2024).

Mee, A. & Snyder, N. (2007) California Condors in the 21st Century - conservation problems and solutions. In: 243–279.

Meretsky, V.J., Snyder, N.F.R., Beissinger, S.R., Clendenen, D.A. & Wiley, J.W. (2000) Demography of the California Condor: Implications for Reestablishment. Conservation Biology. 14 (4): 957–967. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1523-1739.2000.99113.x (Accessed 29th September 2024).

Stack, M.E. et al. (2022) Assessing Marine Endocrine-Disrupting Chemicals in the Critically Endangered California Condor: Implications for Reintroduction to Coastal Environments. Environmental Science & Technology. 56 (12): 7800–7809. Available from: https://doi.org/10.1021/acs.est.1c07302 (Accessed 19th September 2024).

U.S. Fish and Wildlife Service (2023) California Condor Population Graph, 1980-2022 | FWS.gov. 18 April 2023. Available from: https://www.fws.gov/media/california-condor-population-graph-1980-2022 (Accessed 28th September 2024).

U.S. Fish and Wildlife Service (2020) California Condor Recovery Program 2020 Annual Population Status. Available from: https://www.fws.gov/sites/default/files/documents/2020-California-Condor-Population-Status.pdf (Accessed 28th September 2024).