Lead poisoning and the deceptive recovery of the critically endangered California condor

Abstract

Endangered species recovery programs seek to restore populations to self-sustaining levels. Nonetheless, many recovering species require continuing management to compensate for persistent threats in their environment. Judging true recovery in the face of this management is often difficult, impeding thorough analysis of the success of conservation programs. We illustrate these challenges with a multidisciplinary study of one of the world's rarest birds-the California condor (Gymnogyps californianus). California condors were brought to the brink of extinction, in part, because of lead poisoning, and lead poisoning remains a significant threat today. We evaluated individual lead-related health effects, the efficacy of current efforts to prevent lead-caused deaths, and the consequences of any reduction in currently intensive management actions. Our results show that condors in California remain chronically exposed to harmful levels of lead; 30% of the annual blood samples collected from condors indicate lead exposure (blood lead ≥ 200 ng/mL) that causes significant subclinical health effects, measured as >60% inhibition of the heme biosynthetic enzyme δ-aminolevulinic acid dehydratase. Furthermore, each year, ∼20% of free-flying birds have blood lead levels (≥450 ng/mL) that indicate the need for clinical intervention to avert morbidity and mortality. Lead isotopic analysis shows that lead-based ammunition is the principle source of lead poisoning in condors. Finally, population models based on condor demographic data show that the condor's apparent recovery is solely because of intensive ongoing management, with the only hope of achieving true recovery dependent on the elimination or substantial reduction of lead poisoning rates.wildlife | ecotoxicology | hunting | demography | vulture

Lead Exposure Risk from Trash Ingestion by the Endangered California Condor (Gymnogyps californianus)

“…Exposure to lead ammunition via ingestion of spent ammunition fragments embedded in carcasses is the primary risk factor for lead poisoning in California Condors (e.g., Finkelstein et al 2012), but our results also suggest that ingestion of lead ammunition-related trash may also be an important, albeit much less frequent, source of lead exposure. Thus, our findings suggest that trash ingestion is not a significant contributor to the epidemic lead poisoning rates observed in California Condors ), but ingestion of ammunition-related trash could be of concern and efforts to minimize a condor's exposure to ammunition-related trash are warranted.…”

“…data). Currently, wild California Condors face multiple threats to their recovery, including lead poisoning and trash ingestion (Mee and Snyder 2007;Finkelstein et al 2012;Rideout et al 2012). Although there is clear evidence that ingestion of spent lead ammunition from feeding on carcasses is the principal source of lead exposure to condors (Parish et al 2009;Finkelstein et al 2012) other sources, such as trash ingestion, may also be an exposure risk (Walters et al 2010).…”

Two decades of cumulative impacts to survivorship of endangered California condors in California

“…Among the individuals who underwent chelation therapy, 95% survived treatment and were successfully released back into the wild. The results presented here and by Finkelstein et al (2012) suggest that a stable condor population in California is dependent on continuation of the current level of management interventions, especially those required to mitigate lead poisoning. Finkelstein et al (2012) used survival estimates generated from 2010 data to project an annual condor population growth rate of 1.003 (i.e., approximately stable), assuming no captive-reared releases and the current level of management actions for the population.…”

“…The results presented here and by Finkelstein et al (2012) suggest that a stable condor population in California is dependent on continuation of the current level of management interventions, especially those required to mitigate lead poisoning. Finkelstein et al (2012) used survival estimates generated from 2010 data to project an annual condor population growth rate of 1.003 (i.e., approximately stable), assuming no captive-reared releases and the current level of management actions for the population. Natural recruitment, largely hindered by high nestling mortality Rideout et al, 2012), has yet to compensate for the level of mortality experienced in the population.…”

Terrestrial Scavenging of Marine Mammals: Cross-Ecosystem Contaminant Transfer and Potential Risks to Endangered California Condors (Gymnogyps californianus)

“…8,9 Condors that spend more time on the coast, where they are known to forage on marine mammals, 12 have a higher probability of survival, presumably because of a lower risk of lead poisoning. 11 However, contaminant transfer from feeding on marine mammals is an additional threat as marine-foraging coastal condors had potentially harmful concentrations of DDE (Table 1), and Burnett et al 12 documented that condors breeding along the Big Sur coast of California had a hatching success rate 20−40% lower than that of noncoastal breeders.…”