Aug. 16, 2006 — As saber-toothed cats, mammoths, giant ground sloths and other "mega fauna" disappeared from North America at the end of the last ice age, condors survived the demise of their beloved carrion by switching to seafood, say researchers who study the Pleistocene era.
At the same time — roughly 9,000 to 12,000 years ago — other large meat-eating birds didn't make the switch to coastal fare, and are now extinct.
The evidence of this dietary survival tactic has been found inside the bones of the birds themselves: Different proportions of isotopes of carbon, hydrogen and nitrogen reflect what the birds ate, Kena Fox Dobbs and her team report in this month's issue of the Geology.
"Everybody thinks about mammal mega fauna" and tend to forget there were also huge birds in the Pleistocene era, said Fox-Dobbs, a researcher at the University of California at Santa Cruz.
"Logically it would follow that as the mammal mega fauna disappeared, so did the avian mega fauna. We set out to test that," she said.
The largest of the Pleistocene birds were black vultures and hang-glider-sized "teratorns" — which are now extinct. The condor, on the other hand, survived in the coastal ranges of California after having once soared from coast to coast, Fox-Dobbs explained.
Testing condor bones recovered from the Rancho La Brea and McKittrick tar pits in Southern California, the team discovered that the condors that died there ate land animals and seafood.
The bones of teratorns and black vultures from the same locations, however, show isotopic signatures of exclusively terrestrial diets.
"I think this is a beautiful study," said Matthew Kohn, a geochemist at the University of South Carolina. "I think it is quite interesting that there are large carnivorous birds that went extinct at the same time."
The use of three elements in the isotopic studies also makes the work especially rigorous, Kohn said.
Data from other locations in the Southwest, Texas, and Florida show that condors in those areas ate only land animals.
