SIZE AND SHAPE STASIS IN RANCHO LA BREA BARN OWLS OVER THE LAST GLACIAL-INTERGLACIAL CYCLE

Conventional evolutionary biology highlights examples like the Galapagos finches, which show rapid responses to climatic change. We studied the sample of Barn Owls (Tyto alba) from Rancho La Brea to determine if they showed size or shape changes in response to the climate changes of the last 37,000 years. Even though living Barn Owls exhibit a weak Bergmann’s rule effect, with larger body sizes in colder climates, the Rancho La Brea owls showed also complete stasis over this interval, with almost no statistically significant changes in size or robustness even during the peak glacial interval at 18,000-20,000 years ago, when the climate at Rancho La Brea was dominated 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, and Caracaras. Apparently, many birds do not respond to long-term changes in climate in a simple fashion, but are ecologically flexible and live in a wide range of habitats and climates without change in size or limb robustness.