Stasis in the smaller owls from rancho la brea during the last glacial-interglacial climate change

Abstract

Conventional evolutionary biology highlights examples like the Galápagos finches, which show rapid responses to climatic change. Previous studies of many common birds of La Brea, including Teratornis merriami, La Brea Condors (Gymno-gyps amplus), Golden Eagles (Aquila chrysaetos), Bald Eagles (Haliaeetus leucoceph-alus), Californian Turkeys (Meleagris californica), Caracaras (Caracara plancus prelutosus), and Black Vultures (Coragyps occidentalis), as well as the two larger owls, the Great Horned Owl (Bubo virginianus) and the Barn Owl (Tyto alba), showed complete stasis in size and shape through the last glacial-interglacial cycle. Are the smaller birds, especially the small owls, as unresponsive to climate change as the larger birds, or are they more like the Galápagos finches? We measured the large samples of the crow-sized Long-Eared Owl (Asio otus) and the robin-sized Burrowing Owl (Athene cunicularia) from the collections of the La Brea Tar Pits Museum to determine if they showed size or shape changes in response to the climate changes of the last 35,000 years. Even though living Burrowing Owls exhibit a weak Bergmann’s rule effect, with larger subspecies in colder climates, neither species of small owls from Rancho La Brea showed statistically significant changes in size or robustness even during the peak glacial interval at 20,000-18,000 years ago, when the climate at Rancho La Brea was dominated by coniferous forests and snowy winters. Apparently, most 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.