A historical perspective on urban bird research: trends, terms, and approaches

Abstract

As Earth's human population continues to increase and urbanize, it is likely to increasingly affect biodiversity. Avian ecologists have been studying these effects for over a century. Here, we review these studies to: 1) characterize the type of research approaches that have been used, 2) suggest strengths and weaknesses of these approaches, 3) offer a standardized nomenclature for the degree of settlement that will be used throughout this volume, and 4) suggest how our approach can be strengthened to better inform public policy. The majority of urban bird studies were conducted since 1980. The typical study is a one- or two-year correlational investigation of breeding bird relative abundance in the forests of the United States or northern Europe. Experimental studies are rare despite the frequent and replicated land transformations conducted by developers. Studies of birds in tropical, urban settings are especially rare. This is problematic because human populations are expected to rapidly grow and urbanize in such regions and biodiversity there is rich. Recognizing trade-offs among study duration, spatial extent, and mechanistic understanding, we suggest that researchers use short-term, correlational studies of the entire gradient of urbanization to inform long-term, mechanistic studies of bird populations. We define five points along the gradient of urbanization for consistent use throughout this volume (wildland, exurban or rural, suburban, and urban; Table 1.1). These are useful for categorizing study areas at the landscape scale (>1km2). Briefly, wildlands are unsettled lands that may occasionally include dwellings. Rural and exurban lands are sparsely settled by individual homesteads, recreational development, and small towns (they are distinguished by the surrounding matrix: rural = agricultural, exurban = native habitat). Suburban lands are characterized by moderate- to high-density, single-family housing with lot sizes of 0.1-1.0 ha. Urban lands are primarily covered by multi-family and/or multi-storied buildings. Urban bird studies would more effectively inform policy, planning, and management if they were more relevant, rigorous, compelling, and visible. We suggest that this can be accomplished by 1) understanding how development pattern affects birds, 2) increasing study of birds in tropical urban areas, 3) increasing the use of experimental, mechanistic investigations, 4) using landscape ecological metrics to quantify the urban settings we study, and 5) distilling clear graphs or photographs of important results.