A late Pleistocene nest cave of Gymnogyps californianus (California Condor) in Texas: New radiocarbon and stable isotope analyses

Fossil remains of Gymnogyps californianus (California Condor) from Mule Ears Peak Cave, Big Bend National Park, Texas, recovered in the 1930s were reexamined to determine a precise age for nesting condors in this region. Bones of at least 6 prefledged chicks account for most (15, or 65%) of the 23 skeletal elements from this cave and a new osteology collection of known-age condor chicks at the U.S. National Museum, Division of Birds, now allows accurate estimate of the age of death of these fossil condor chicks based on their bone development and porosity. Current and previous radiocarbon dates on juvenile and adult bones, respectively, indicate the presence of condors at this site beginning at similar to 15,000 calendar years before present (cal yrs BP), with definite nesting occurring at similar to 13,000 cal yrs BP. Stable isotope analysis (delta C-13 and delta N-15) of bone collagen on 2 bones of adult condors reflects a diet similar to other fossil condors previously analyzed from the inland western U.S. The delta C-13 values in the Mule Ears Peak condors indicate a diet of megafauna that subsisted on C-4 plants in a desert grassland ecosystem. These results support the hypothesis that condors were extirpated from the inland west with the loss of megafauna at the end of the Pleistocene. Further, Big Bend National Park with its vast open space and cliffs and canyons for nesting condors should be considered as an additional release site for captive-reared condors as part of the current Condor Recovery Program.