Bone or hair samples were also collected from potential prey, including Pleistocene bison and horses, as well as dozens of 20th-century mule deer, feral pigs, whales, seals, sea lions and domesticated cattle. "The California Department of Transportation even agreed to go around and snip off hair from dead deer killed on the highway," Chamberlain says. "Other people went around picking up samples from dead seals on beaches. We ended up getting an incredibly large database on hundreds of animals."
The isotopic data revealed that condors are likely to have undergone two major dietary shifts since the Pleistocene. "The first occurred from the end of the Ice Age about 11,000 years ago to historical times, and the second took place between the 18th century and the modern era," Chamberlain says, adding that both events coincide with the arrival of humans in North America.
"During the Pleistocene, condors were distributed across the continent," he explains. "There was plenty of megafauna to feed on, including mammoths, mastodons, camels and bison."
Isotopic analysis of ancient condor bones from the La Brea tar pits revealed that about 40 percent of Pleistocene birds fed primarily on marine species, the rest on a mixture of marine mammals and giant land mammals.
"When the Ice Age ended, most of the terrestrial megafauna vanished," Chamberlain says. "There's a theory that they were killed off by humans, and as a result, the condors that lived inland no longer had large prey to feed on."
The disappearance of terrestrial megafauna caused the first major dietary shift, according to the authors. "Our paper shows that condors on the West Coast survived the Ple