HOW DID SMALL OWLS FROM THE LA BREA TAR PITS RESPOND TO THE LATE PLEISTOCENE CLIMATE CHANGE?

Classic cases of modern bird evolution, such as the rapid response of Galápagos finches to climate fluctuations, make them the textbook example of evolution. However, all previous studies of common birds from Rancho La Brea (Teratorns, Condors, Black Vultures, Golden Eagles, Bald Eagles, Turkeys, and Caracaras) have demonstrated stasis through the climatic extremes of the last glacial-interglacial cycle. This is also true of the Great Horned Owl and Barn Owl. But would smaller species be more likely to respond to climatic fluctuations than larger species? To test this, we examined specimens of the two common small owls (the Long-Eared Owl Asio otus, and the Burrowing Owl Athene cunicularia) from the La Brea Tar Pits Museum collections to determine changes in size or limb robustness over the last 35,000 years in response to climate changes. Living owls display a weak Bergmann’s rule effect, with larger body sizes in colder regions. Despite this effect, all the large and small La Brea owls maintained stasis over this period with little significant change in size or robustness despite climate changes over the peak glacial maximum 18,000-20,000 years ago, during which the climate at La Brea consisted primarily of snowy winters and coniferous forests. Our results concur with previous research on all the La Brea birds, which all show stasis through the entire range of dated pits. It seems birds do not respond to climate change in a simple manner, they are adaptable to many environments and may live in various ecosystems and climates without much change in body size or limb robustness over time.