For the Birds Radio Program: DDT and California Condors
Last month, I got to spend time in California’s Big Sur country, savoring amazing views of at least ten different California Condors, all flying or perching, wild and free. That made September 15 one of the most thrilling days of my life.
But when I got home and started researching the individual condors I’d seen and photographed, up close and personal, my elation was tempered by sobering facts.
Condor #167, nicknamed “Kingpin,” currently one of the oldest condors living in the wild, was hatched in 1997 at the Los Angeles Zoo, and was released to the wild 7 months later. He and his mate have successfully reared two chicks, but not from their own eggs—they incubated and reared eggs that had been laid by captive birds. This pair’s first egg never hatched because of eggshell thinning. Meanwhile, many of the eggs produced by condors along the coast are failing, due to extremely thin eggshells. Twelve out of 16 Big Sur condor nest sites failed between 2007 and 2009. Fragments of shells—all visibly thin—were recovered from those sites. Meanwhile, the condors released farther south, where the birds are not feeding on sea mammal carcasses, have enjoyed a 70 to 80 percent hatching rate. Studies from 1994 to 2006 found high levels of DDT and related compounds in California sea lion blubber. These marine mammals live near the Palos Verdes Shelf Superfund site, an underwater region contaminated by an estimated 1,540 metric tons of DDT discharged by the Montrose Chemical Corporation’s DDT manufacturing plant between the 1950s and 1970s. Current research about to be published in the journal The Condor finds that eggshell fragments recovered in the Big Sur region were 34 percent thinner than eggs laid at the same time in the southern reintroduction zone, and lack the normal external crystalline layer.
The U.S. banned the use of DDT in 1972 after studies by Joseph Hickey of the University of Wisconsin and others linked it to eggshell thinning in Bald Eagles, Peregrine Falcons and other species. The pesticide was linked to other health hazards in wildlife and humans, and was being found in disturbing levels in human breast milk. Tragically, banning a substance doesn’t magically make it disappear, and DDT is exceptionally persistent.
DDT isn’t killing birds outright, as lead is doing. Some condor chicks from other areas are not surviving the nestling stage because their food is laced with lead. Figuring out how to remove DDT that is already out there is way, way trickier than banning the lead shot and bullets that are the primary source of lead in carcasses, so it makes sense that conservationists focused first on a ban on lead ammunition. Condors away from the coast are more likely to produce healthy eggs, but they and their chicks are more vulnerable to outright death via lead poisoning. At least one of the birds I got wonderful looks at, #418, tested for high lead and had to go in to the Los Angeles Zoo for treatment, but she came though okay. Lead is the critical issue for individual survival right now, but if the species is to ever become self-sustaining, something must be done about the DDT in the sea mammals they’re eating. More and more people are giving up on condors as a doomed species, but doing something about the DDT in the water would be good for sea lions as well. We aren’t a species that likes to clean up our own messes, are we?