Condors are still dying from lead poisoning - but the lead ban has made a difference.
Updated: May 2
Behavioral shifts mask the success of legislation and outreach for endangered species recovery
[Abstracted from the full article above.]
A fundamental challenge in conservation is assessing the efficacy of recovery actions to optimize endangered species management. One iconic example is efforts to recover the critically endangered California condor (Gymnogyps californianus), whose leading cause of death is poisoning from ingesting lead-based ammunition in carcasses. Despite enormous resources expended in California, including implementation of public outreach campaigns and two legislative bans on lead ammunition, lead-related mortality of condors has increased.
Here the authors show that two types of behavioral shifts explain the observed increases in condor lead exposure: "wilder" foraging and ranging by condors and increased shooting of wild pigs (Sus scrofa) by humans. After accounting for these trends, they show that both lead ammunition bans and public outreach efforts have significantly reduced condor blood lead levels in California, lowering mortality. Their analyses uncover a dynamic in which changing ecological conditions mask the true efficacy of legislation and outreach.
Condor feeding on wild pig carcass. Photo: Gavin Emmons.
There has been a paradox of rising condor lead exposures in California despite significant efforts to limit lead-based ammunition use. Rising lead exposure has coincided with increasingly "wild behavior" by condors. Foraging and ranging behavior became "wilder" over the 27-year study period—condors fed less often on lead-free carcasses at feeding stations and also spent less time near release sites. In looking at all observed increases in blood lead over the last 27 years, the Southern (central) flock required additional model factors, in particular changes in wild pig hunting, to explain increases in blood lead.
The authrors' study results indicate that after 2019, deer hunting actually benefited condors in the Southern flock, suggesting that deer hunters produced enough lead-free gut piles to offset lead-contaminated sources. Conversely, wild pig hunt levels were associated with increased condor blood lead after 2019, highlighting pig hunting ("culling") as an emerging source of lead for Southern flock condors. Educating the public about lead toxicity, as well as bans on the sale of lead ammo, have been more effective than has been previously recognized.
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