Old Enemy Puts California Condors at Risk

San Diego Zoo Global

The California condor is the largest land bird in North America. These magnificent birds once ranged from the Rocky Mountains to the Pacific Coast. By the mid-20th century their range had been diminished by human activity to mountainous areas in Southern California. Condors feed on carrion acting as nature’s clean-up crew. This diet makes them susceptible to a variety of contaminants including lead fragments in carcasses, poison bait, and environmental pollutants. 

In 1987, faced with limited success after over two decades of efforts to preserve the species in the wild, the last 22 wild California condors were captured and a concerted effort was mounted to preserve condors in captivity with the goal of ultimately returning them to the wild. That effort is one of the great success stories in zoological intervention.

Today, California condors are back in the wild, fulfilling the goal of establishing two distinct breeding populations – one in California – extending into Mexico (Baja peninsula), with the second along the Utah/Arizona border.  A third breeding population is maintained in captivity as insurance for the species. 2018 statistics offer evidence of the success of the decades long project – from that low of 22 condors in 1987, there are now 312 California condors in the wild, with 176 individuals in captivity.  
The species is still listed as Critically Endangered and recovery in the wild is perilous.  A new study from San Diego State University (SDSU) suggests an old enemy of the condors still presents a danger to their future.  SDSU researcher Maggie Stack has discovered residual chemicals from DDT pesticides including the compound TCPM in blood samples from the wild condor population.

Stack’s preliminary findings have shown that coastal condors have approximately 44 of these chemical compounds in their blood samples, whereas the inland populations have about 18. This striking difference between the two populations has led researchers to consider whether those 25 compounds strictly observed in the coastal samples could be the root of the endocrine disruptors. The chemical of interest for Stack and her team is called tris(4-chlorophenyl)methane (TCPM), which is an impurity from the notorious insecticide DDT. The pollutant is still persistent in the environment, despite being outlawed in the 1970s.

These compounds tend to be considered endocrine disruptors, which leads to poor reproductive success, and ultimately the inability for the condors to replenish their population,” says Stack.

There is a large volume of research that demonstrates the persistence of concentrations of DDT and TCPM in marine mammals. The same animals that as their carcasses wash up on the California coast end up as part of the coastal condors’ diet. The danger that this poses to condors is due in part to the unique nature of their digestive system.

“The immune systems of condors are exceptional, and critical for the health of the environment [because] they are able to break down pathogens from their prey, preventing the spread of these compounds into the environment,” said Stack. This makes condors especially susceptible to contaminants from, and partially explains the near collapse of the species in the 1970s and 80s with the use of harmful pesticides or lead bullets from hunting.

The damage done and danger created by DDT and other Persistent Organic Pollutants was formally recognized by the 182 parties (181 countries and the European Union) which have signed on to the Stockholm Convention on Persistent Organic Pollutants. However, even if all use of these chemicals was terminated (and many of them are still in production) their effects will be felt for decades and species such as the California condor will remain at risk.