DENVER--A cosmopolitan diet may have helped the California condor avoid the fate of many other large scavenging birds 12,000 years ago, a paleontologist reported here today at the annual meeting of the Society of Vertebrate Paleontology.
The late Pleistocene was a difficult time for large animals in North America. Climate was changing, and human hunters had marched into the continent. Although the ultimate cause of the extinction of the mammoths and other large herbivores is still debated, it's clear that their demise had drastic effects that cascaded through food webs. Saber-toothed cats and other predators went extinct as well, as did many kinds of vultures, including Teratornis Merriam--the largest flighted bird ever, with a wingspan of 3 meters or more. Yet the California condor pulled through.
Kena Fox-Dobbs of the University of California, Santa Cruz, hypothesized that the reason might be that condors had broader diets that included marine mammals, which did not suffer drastic extinctions. To test the idea, she examined the isotopes in the bones of three species of fossil birds: the California condor, Teratornis, and the extinct western black vulture--all of which were common in southern California until the end of the Pleistocene. Ecologists have established that nitrogen and carbon isotopes are heavier in marine organisms.
The two extinct scavengers had isotopes, preserved in bone collagen, that indicated they were eating carcasses of land animals. In contrast, the condor bones from southern California suggested they were also noshing on dead seals and other marine animals. "That wide dietary niche was key to their survival," Fox-Dobbs says. Boosting the argument, condor fossils from New Mexico and Florida indicate that the birds had terrestrial diets--and didn't survive there. (Food from the ocean would have been less plentiful in Florida, which lacks the currents that bring nutrients up from the sea floor off California.)
"It's a novel study," says paleontologist John Alroy of the National Center for Ecological Analysis and Synthesis in Santa Barbara, California. "As far as paleontological evidence goes, it's pretty convincing." The broader diet could explain why condors were able to survive despite the loss of many large animals. "To hang on for 12,000 years, you've got to be doing something right."