Designing research to advance the management of birds in urbanizing areas

Managers charged with maintaining self-sustaining populations of native wildlife in urbanizing areas can protect habitat reserves and encourage development styles that minimize negative impacts on wildlife. Unfortunately, few data are available to guide these activities with respect to bird conservation. Studies are needed that determine principles of reserve design and development pattern that maximize reproduction and survivorship of native birds. Good experimental design is needed to insure such studies have strong inference. To optimize our ability to relate changes in urban areas to biodiversity we need to consider how to (1) select research sites, (2) describe the urban gradient, (3) quantify wildlife community parameters, (4) quantify wildlife population parameters, and finally (5) identify the mechanisms affected by human activity that link population level processes to community level patterns. We provide advice for these decisions from our ongoing studies of reserves and developments in the Seattle, Washington area. We encourage researchers to combine correlational and experimental studies to determine the mechanisms that link human activity to bird population viability. Especially useful studies will elucidate how the pattern of human settlement and the properties of reserves affect several important possible limiting factors (nest predation, food or nest site availability). Understanding of how local and landscape-level condition affect limiting factors allows managers to design ways to reduce effects on populations. Prescriptions for maintaining native bird communities should be built from such mechanistic understanding of how to protect several populations. Community prescriptions should not be built from simple measures of community composition because presence of a species may not indicate viability. It is important to measure reproduction and survivorship of individuals in urban landscapes. Direct measurement of reproduction should be supplemented with multiple indirect measures (e.g. ratio of juveniles to adults, rates of predation on artificial nests) to increase accuracy. Important limiting factors (e.g. nest predators, brood parasites, food sources) should be studied to determine how human activity directly affects them. Well designed studies provide managers with the information they need to accurately determine how a combination of reserves and developments of varying density and pattern combine to maintain native bird populations in an urbanizing environment.