The critically endangered California Condor (Gymnogyps californianus) is an avian scavenger and North America’s largest flying bird (West et al. 2017).  They have been experiencing population declines since the early 1950s and in 1980, the entire species consisted of only about 30 individuals.  Many doubted that these symbolic birds would do very well in captivity, but in 1987, all 27 of the remaining California Condors were captured and brought to a captive breeding facility. Teams of researchers from organizations such as the U.S. Fish and Wildlife Services, the Los Angeles Zoo, and the San Diego Wild Animal Park came together for these birds and by 1998, there were more than 150 California Condors (Meretsky et al. 2000). Today, there are now five breeding and release facilities in California and Mexico. There are now more than 400 California Condors, and half of these are flying free (National Park Service 2017).

So what was it that caused this species to drop to such small numbers in the first place? When scientists first started looking into this, they discovered that adults had higher mortality rates than immature condors (Meretsky et al. 2000). This was puzzling until they were able to study the tissues of dead condors and obtain blood samples from those that were captured for the captive breeding program. In the mid-1980s, lead poisoning was determined as the leading cause of death in wild California Condors (Wiemeyer et al. 1988).

Lead contamination is responsible for the deaths of millions of birds annually, and the main source of this is from hunting. California Condors are a scavenger species that feed on the carcasses of dead animals, and oftentimes they are feeding on carcasses that have been shot by hunters. Lead bullets, common ammunition used by hunters, shatter into tiny fragments upon impact. Because California Condors are known to scavenge communally, a single carcass containing these bullet fragments can poison several individuals (Kelly et al. 2014). Lead exposure was found to increase during hunting seasons. Sudden, severe symptoms of lead poisoning might include labored breathing, incoordination, and blindness. Chronic symptoms, which take longer to develop, might include changes in migratory movements or changes in bone mineralization, which increases the risk of bone fractures. The final stage of lead poisoning is death (Plaza and Lambertucci 2019).

Although eliminating lead from their environment is critical for the recovery of the California Condor, is it important to note that this is not the only contaminant that is threatening this species. Although California banned DDT in 1972, its influences are very present in this ecosystem today. DDE, a byproduct of DDT that does not get excreted from the body and actually becomes more concentrated over time, is consumed by the condors when they feed on marine mammal carcasses. Once ingested, DDE causes thinner eggshells, which increases the risk of the eggs breaking before the offspring have had a chance to develop (Kiff et al. 1979). Scientists have found that DDE disrupts the endocrine system of California Condors by changing the concentrations of reproductive hormones in their blood and the number of receptors that the hormones can send their signals to, which is what is ultimately causing the thinner eggshells. How lead is influencing the endocrine system in this species is not understood (Felton et al. 2015). Before we can fully address these contaminants that are reducing reproductive success through egg breakage, we need to focus our attention on reducing the amount of lead in the environment so we can increase the number of adults even attempting to nest.

The last two decades have seen the number of free-flying California Condors go from 0 to nearly 200 individuals. The real question is: are these birds still being affected by lead poisoning?

In 2008, California banned the use of lead ammunition for most hunting activities within the wild California Condor range. Annual blood samples found that the percent of these condors with more than 10 micrograms of lead per deciliter of blood was 67% prior to this ban (data from 1997-2008) and 62% after the ban (from 2008-2011) (Kelly et al. 2014). These results indicate that despite this ban, California Condors are still experiencing chronic exposure to lead poisoning. Because of this, California has decided to enact a state-wide ban on the use of lead ammunition for hunting, which is set to go into full effect on July 1, 2019. Perhaps this will be the key to the success of one of our country’s longest-running conservation programs. 

References:

Felton RG, CC Steiner, BS Durrant, DH Keisler, MR Milnes, and CW Tubbs. 2015. Identification of California Condor estrogen receptors 1 and 2 and the activation by endocrine disrupting chemicals. Endocrinology 156(12): 4448-4457.

Kelly TR, J Grantham, D George, A Welch, J Brandt, LJ Brunett, KJ Sorenson, M Johnson, R Poppenga, D Moen, J Rasico, JW Rivers, C Battistone, and CK Johnson. 2014. Spatiotemporal patterns and risk factors for lead exposure in endangered California Condors during 15 years of reintroduction. Conservation Biology 28(6): 1721-1730.

Kiff LF, DB Peakall, and SR Wilbur. 1979. Recent changes in California Condor eggshells. Oxford University Press 81(2): 166-172.

Meretsky VT, NFR Snyder, SR Beissinger, DA Clendenen, and JW Wiley. 2000. Demography of the California Condor: Implications for Reestablishment. Conservation Biology 14(4): 957-967.

National Park Service. 2017. Condor Re-introduction & Recovery Program. https://www.nps.gov/articles/california-condor-recovery.htm

Plaza PI and SA Lambertucci. 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 (1): 409-417.

West CJ, JD Wolfe, A Wiegardt, and T Williams-Claussen. 2017. Feasibility of California Condor recovery in northern California, USA: Contaminants in surrogate Turkey Vultures and Common Ravens. The Condor: Ornithology Applications 119(4): 720-731.

Wiemeyer SN, JM Scott, MP Anderson, PH Bloom, and CH Stafford. 1988. Environmental contaminants in California Condors. The Journal of Wildlife Management 52(2): 238-247.

Images:

All images were taken by former coworker, Louise Prévot, in Marble Canyon, AZ.