STASIS IN RANCHO LA BREA BLACK VULTURES (CORAGYPS OCCIDENTALIS) OVER THE LAST GLACIAL-INTERGLACIAL CYCLE

In textbooks, bird evolution is often modeled on the example of the Galapagos finches, which show rapid responses to climatic change. We studied the sample of Pleistocene relative of the Black Vulture (Coragyps occidentalis) from the Rancho La Brea to see if they showed size or shape changes in response to the climate changes of the last 35,000 years, including the last complete glacial-interglacial cycle. Even though living Coragyps atratus shows a strong Bergmann’s rule effect, with larger body sizes in colder climates and smaller subspecies in the tropics, the Rancho La Brea Black Vultures showed no statistically significant change over this interval, with no meaningful changes in size or robustness. This was true even during the peak glacial interval at 18,000-20,000 years ago, when the region was covered by coniferous forests and snowy winters. These results are consistent with earlier studies on La Brea Condors, Golden Eagles, Bald Eagles, Turkeys, Great Horned Owls, Barn Owls, and Caracaras. In contrast to the Galapagos finches, Rancho La Brea birds do not respond rapidly to long-term changes in climate in a simple fashion. Instead, they are ecologically flexible and live in a wide range of habitats and climates without change in size or limb robustness