The number of condors treated by the zoo in October is about half seen in a typical year, the Los Angeles Times reported.
Adam Keats, senior counsel and urban wildlands program director for the Center for Biological Diversity, said the high amount of lead poisoning being seen in condors is likely linked to hunting. "There's a wide use of lead ammunition in condor habitats. The availability of lead needs to be reduced by sale and stocking," Keats said.
Lead poisoning is the leading cause of death among juvenile and adult condors, said Curtis Eng, chief veterinarian at the zoo, adding that at least one bird had died of lead toxicity earlier this year.
"That's scary to see so many clinically sick birds," Eng said in a statement.
The announcement from the zoo comes just weeks after California Gov. Jerry Brown signed legislation requiring hunters to use non-lead ammunition in an effort to curb the amount of lead being passed on from carcasses to scavenging animals, such as condors.