A few of the CondorWatch Scientists just published a new paper in the journal Environmental Science and Technology documenting that condors eating marine mammals carcasses along the Big Sur Coast of California are exposed to potentially harmful contaminants.
Because marine mammal carcasses can be an abundant food source for condors and are thought to have helped prevent their extinction at the end of the last ice age, people welcomed the inclusion of marine mammals on the condor’s menu. However, marine mammals, and California sea lions in particular, are known to contain high levels of toxic chemicals such as DDE, the main breakdown product of the agricultural pesticide DDT. Now you might be thinking “But DDT was banned for use in the United States decades ago?” Yes, that is true, but unfortunately DDE is very persistent and is still around today – especially in tissues of marine predators such as California sea lions.
DDE has been shown to cause eggshell thinning and reduced hatching success in birds and DDE exposure has been linked to population declines of multiple species, including the bald eagle, peregrine falcon, and brown pelican.
Our new study estimated that about 40 percent of breeding-age coastal condors have DDE levels at or above levels that caused eggshell thinning in bald eagles and about 20 percent meet or exceed levels associated with nest failure in bald eagles. A prior study led by one of our condor collaborators, Joe Burnett with the Ventana Wildlife Society, has documented that condors on the coast have thinner eggs and reduced hatching success compared to condors that breed inland.
So, what do we do? Well we do know that lead poisoning is the number one cause of condor mortality and our prior work has shown that if we eliminate or greatly reduce lead poisoning the condor population can recover. However, it is worrisome that condors ingest DDE along with a full cocktail of other contaminants when feeding on marine mammals, especially California sea lions. Our team is currently working to assess the effects of decreases in nesting success due to DDE on condor recovery.
Ultimately, our study highlights a harsh reality: we are all being exposed to multiple contaminants throughout our lives — even us humans! We should do what we can to minimize exposures we have the most control over (lead-free ammunition anyone?!) and also push to reduce our use of toxic chemicals as individuals and as a society.
In the end the condor is one tough bird and we are hopeful that even though DDE might be a hurdle that impacts some coastal birds, across California condor chicks will keep hatching and the numbers of condors soaring in the sky will continue to grow.