JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. University of California Press and Cooper Ornithological Society are collaborating with JSTOR to digitize, preserve and extend access to The Condor.Abstract. Urbanization leads to the biotic homogenization of global avifauna. We hypothesized that urbanization acts as a filter on species traits and, therefore, that urban passerines share biological traits explaining their capacity to tolerate urban constraints. We investigated 18 biological traits of passerines related to their general biology, distribution, breeding, and morphometry. In a regional analysis conducted on passerine data from one Swiss and 11 French cities (regional analysis), we identified urban adapters (tolerant species) and urban avoiders (intolerant species), and compared their traits. In a local analysis conducted on passerine data of 13 woodlands located along a short rural-urban gradient, we identified groups of species associated with particular vegetation structures within or particular landscape structures around woodlands. We associated each of these species groups with a tolerance level to urbanization and compared their traits. Regional analysis revealed that urban adapters prefer forest environments, are sedentary, omnivorous, widely distributed, high-nesters with large wingspans. Urban avoiders seem to allocate more energy to reproduction than do urban adapters, to the detriment of adaptation to new environments such as urban areas. Local analysis did not reveal any link between traits and species tolerance levels. At large spatial scales, urbanization seems therefore to act as a filter on species traits. However, the urban constraints that filter species at such large scales do not seem to be the same ones that determine species distribution at local scales. Analyses of traits are powerful tools to understanding regional community composition between urban and rural areas. ¿Actúa la Urbanización como un Filtro para las Aves de acuerdo a sus Rasgos Biológicos?Resumen. La urbanización conduce a la homogenización biótica de la avifauna global. Nosotros hipotetizaLa urbanización conduce a la homogenización biótica de la avifauna global. Nosotros hipotetizamos que la urbanización actúa como un filtro sobre los rasgos de las especies, y, por lo tanto, que las aves paserinas urbanas comparten rasgos biológicos que explican su capacidad para tolerar las limitaciones impuestas por el ambiente urbanizado. Investigamos 18 rasgos de las aves paserinas relacionados con su biología general, distribución, reproducción y morfometría. En un análisis regional realizado con datos de aves paserinas de una ciudad suiza y 11 ciudades francesas, identificamos especies que se adaptan al ambiente urbano (especies tolerantes)...

Suggestions of collapse in small herbivore cycles since the 1980s have raised concerns about the loss of essential ecosystem functions. Whether such phenomena are general and result from extrinsic environmental changes or from intrinsic process stochasticity is currently unknown. Using a large compilation of time series of vole abundances, we demonstrate consistent cycle amplitude dampening associated with a reduction in winter population growth, although regulatory processes responsible for cyclicity have not been lost. The underlying syndrome of change throughout Europe and grass-eating vole species suggests a common climatic driver. Increasing intervals of low-amplitude small herbivore population fluctuations are expected in the future, and these may have cascading impacts on trophic webs across ecosystems.