Microbiology and Environmental Toxicology Department, University of California, Santa Cruz, CA 95064, USA.
Proc Natl Acad Sci U S A. 2012 Jul 10;109(28):11449-54. doi: 10.1073/pnas.1203141109. Epub 2012 Jun 25.
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.
濒危物种恢复计划旨在将种群数量恢复到自我维持的水平。然而，许多正在恢复的物种需要持续的管理，以弥补其环境中持续存在的威胁。在这种管理下判断真正的恢复往往很困难，这阻碍了对保护计划成功的全面分析。我们通过对世界上最稀有的鸟类之一——加州秃鹰（Gymnogyps californianus）的多学科研究来说明这些挑战。加州秃鹰曾濒临灭绝，部分原因是铅中毒，而今天铅中毒仍然是一个重大威胁。我们评估了个体与铅相关的健康影响、当前预防铅中毒导致死亡的措施的效果，以及减少当前密集管理措施的任何后果。我们的研究结果表明，加利福尼亚的秃鹰仍然长期暴露在有害的铅水平下；从秃鹰身上采集的年度血液样本中有 30%表明存在铅暴露（血液中的铅含量≥200ng/ml），这会导致显著的亚临床健康影响，表现为血红素生物合成酶 δ-氨基-γ-酮戊酸脱水酶的抑制率超过 60%。此外，每年约有 20%的自由飞翔的鸟类血液中的铅含量（≥450ng/ml）表明需要进行临床干预，以避免发病率和死亡率。铅同位素分析表明，含铅弹药是秃鹰铅中毒的主要来源。最后，基于秃鹰人口统计数据的种群模型表明，秃鹰的明显恢复仅仅是因为正在进行的密集管理，实现真正恢复的唯一希望取决于铅中毒率的消除或大幅降低。
