Some troublesome themes in this world just won’t go away: bigotry, war, violence against innocents, abject poverty, corruption and disease, to name a few. In the natural world — the only one we have — the troublesome threats to wildlife are caused by loss of habitat, pollution and pesticides, including the champion of all hazards, DDT.
Yes, that damnable DDT is the most sinister wildlife archenemy in generations. It was banned in 1972, yet it refuses to go away. Indeed, it continues to wreak havoc on the reproductive abilities of birds, including the critically endangered California condor.
A recent report in the peer-reviewed Environmental Science & Technology (Kurle, et al) said DDE (a major metabolite of DDT) has been found in the blood of 40 percent of coastal condors. As a result, those condors’ eggshells are thinner than normal — resulting in reduced breeding success.
If DDT has been banned for 44 years, why is it still a menace to wildlife? Condors eat carrion (dead animals), and coastal condors are known to feed on carcasses of sea lions. These marine mammals have high levels of DDE, mercury and PCPs, because their mating grounds are in waters contaminated by the largest DDT dump site in the U.S. — the Palos Verdes Shelf.
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To wit, sea lions eat DDT-contaminated fish, and when condors’ dine on sea lion carcasses the DDE (lodged in the fat of the critters) insidiously modifies condors’ calcium metabolism, resulting in thinner eggshells.
The Montrose Chemical Corp., a DDT manufacturer, fashioned an environmental catastrophe by disposing of an estimated 1,700 tons of DDT into the Pacific Ocean off the coast of Palos Verdes from the late 1950s to the early 1970s.
The DDT residue (which degrades very slowly) reportedly spread out to more than 17 square miles of ocean floor.
Brief history of DDT contagion
Condors aren’t the first birds threatened by the reckless legacy of DDT dumping. The brown pelican population was nearly decimated a few years ago. Bald eagles, peregrine falcons, ospreys, starlings and songbirds have experienced thinning eggshells as well.
The public was first alerted to the deadly impact of DDT on wildlife in 1962 when biologist and author Rachel Carson published “The Silent Spring,” detailing the devastation DDT causes to wildlife and the environment. Notwithstanding the brutal verbal attacks she endured from conservative think tanks and the chemical industry, Carson was correct.
Looking specifically at condors and DDT, the Cooper Ornithological Society’s empirical studies in 1979 (author, Lloyd Kiff) showed condor eggshell fragments recovered from 1896 to 1943 averaged 0.79 mm thick; but eggshell fragments recovered from condors between 1964 and 1969 averaged just 0.54 mm thick. Those later eggshells were 32 percent thinner than in the pre-DDT era, which began in the late 1940s when it was used to reduce mosquito populations.
Implications for coast condors
executive director of the Ventana Wildlife Society Kelly Sorenson and VWS Biologist Joe Burnett, answered questions raised by the latest research. Sorenson made clear that of the 268 condors flying free (155 in California), only about a third feed on coastal carrion, and the others (inland in southern California and Arizona) are not impacted by DDE.
Regarding the Kurle article’s assertion that “Deaths (of condors) have largely outpaced successful births in the wild,” Sorenson said those data reflect the entirety of the California Condor Recovery Program dating back to the 1980s.
However, “in 2015, there were more births (14) than deaths (12) in the wild … so we are optimistic. Lead is our biggest concern,” Sorenson said, noting that condors eating the carrion of deer and other critters that were shot with lead ammunition become victims of lead poisoning — and many die.
In 2014 and 2015 the VWS distributed (free) about $50,000 worth of nonlead ammunition to hunters. Sorenson said he believes the switch from lead to copper bullets is the reason there was only one lead-poising-related condor death last year, whereas six condors died of lead poisoning three years ago.
Regarding eggshell issues in the Big Sur and Pinnacles area (mature adults raise one chick a year, and presently there are four active nesting pairs raising chicks), Sorenson characterized the level of eggshell thinning to be “near the threshold and far better than the peak of the problem in other species such as the bald eagles. At one time, they couldn’t lay a viable egg to save their life — literally.”
Biologist Burnett, who has made several pilgrimages to Cambria to share updates on the seven juvenile condors released in the mountains above San Simeon in November, said he hopes in time Central Coast condors will feed on the carcasses of elephant seals, considered “a low DDE risk as compared to the highly DDE contaminated sea lions.”
The seven juveniles have GPS technologies attached to their wings, and they have been documented feeding on sea lions in the Big Sur area; but as of yet have they not dined on elephant seal carcasses.
However, because the juveniles won’t begin breeding for three or four years, “they are at a lower risk of suffering nest failures from DDE.”
What about mature Central Coast condors that feed on sea lions?
“Condors can be exposed to lower levels of DDE and still lay healthy, viable eggs,” Burnett said. “We have learned through our research that condors and their eggs are incredibly resilient and that, despite exposure to dangerous levels of DDE, they still manage to reproduce successfully in the wild.
“They are truly survivors,” he said.
Indeed, these giant birds with 9.5-foot wingspans are all survivors, given that there were only about 22 in the wild in 1982 — down from many thousands at one point — when the decision was made to capture those few birds and launch a captive breeding program.
The naysayers back then who advocated allowing the birds to become extinct were on the wrong side of history.
That said, it’s also true that the 268 California condors flying free today are not yet a truly sustainable community. But people like Sorenson and Burnett, and the many committed wildlife volunteers and professionals, are betting on and working toward an optimistic future for condors, notwithstanding the challenges of DDT and lead.
Freelance journalist John FitzRandolph’s column appears biweekly and is special to The Cambrian. Email him at firstname.lastname@example.org.