Scientists catch and test the condors that ate squirrels shot with lead-based bullets.

Monterey County condors made national news last week when 11 of the 13 condors from Pinnacles National Monument were observed feeding on dead squirrels. Biologists feared that the squirrels had been shot with lead-based ammunition or poisoned by rodenticide. Lead bullets can shut down birds’ digestive systems, which causes death.

Biologists worried the condors may have been poisoned.

In order to keep a close eye on the birds, wildlife officials laid traps for the condors last week. They caught two of the birds on Friday.

Field tests revealed higher-than-normal traces of lead in their blood, according to Kelly Sorenson, executive director of the Ventana Wildlife Society. But, Sorenson says, it doesn’t look like the birds have been poisoned.

“We found that the two birds we trapped both had readings of 30 [micrograms per deciliter],” Sorenson says.

Biologists have traditionally agreed that lead readings up to 20 qualified as relatively safe, “background” levels of exposure, Sorenson says, but some are now reconsidering those levels.

“A lot of us now are thinking that they shouldn’t have more than 10 to 15,” he says. “Over 30 is exposed. Up around 60 is considered clinically affected and up to 100 is poisoned. So these two birds were exposed but not poisoned.”

However, Sorenson says that lead in condor blood has a half-life of 13 days. The birds’ exposure to the lead was 13 days prior to their capture. “So it’s possible that those two birds had a value closer to 60,” he says.

The problems began when wildlife biologists observed the condors eating the carcasses of ground squirrels. Lead-based ammunition and canisters of rodenticide were found nearby, sparking the concern and nationwide media interest.

Sorenson says the effects of rodenticide—unlike lead—on birds that scavenge on poisoned squirrels are largely unknown. “Rodenticides are controlled by federal, state and county officials but they are legally used,” he says. “What we need to focus on is the lead because that’s truly a danger.”

Despite the encouragingly low level of lead found in the blood of the two captured birds, biologists continue to try and trap the other birds.

“Our real concern is that you have a cumulative effect,” explains park superintendent Eric Brunneman. “[The lead] collects in the bone and it’s in them for a long time, so if they go out and do this again, we may have a real problem.”

If biologists find more condors, and determine that the birds are contaminated, they will be taken to the Los Angeles Zoo for surgery or treatment.

“It depends how badly poisoned and how many birds,” Sorenson says. “We can handle a few at once. If they’re acutely poisoned they’re better off down in LA where they have more facilities and technology.”

Sorenson says his primary concern is minimizing the condors’ exposure to lead by educating local ranchers and hunters about the dangers of lead-based bullets and providing economically viable alternatives.

Tensions between biologists and local ranchers and hunters have simmered since the condors were first released into the 25,000-acre Pinnacles National Monument in 2003. Some cattle ranchers fear that if the endangered condors rebound, the birds will threaten their livelihood. Biologists worry that the lead-based ammunition used by locals will wipe out the fragile population.

Sorenson will publish the first paper on the topic later this year and is developing a coupon program to facilitate the availability of a new, non-lead bullet composed of tin, tungsten and bismuth.

“We’re working on a coupon program where ranchers and hunters would redeem coupons with participating stores to receive free non-lead ammunition,” Sorenson says. “We want to get the word out that there are non-lead alternatives for all calibers. This kind of ammo is not widely available, there are some false horror stories about the stuff, and it’s a little more expensive, so we want to make it easier for people to get it. Hunters and ranchers need an opportunity to solve the problem.”