Dispersal, habitat use, and survival of native forest songbirds in an urban landscape
Because movement between habitat patches isolated by urban development may be necessary for bird populations to remain viable, I examined correlates between land cover, bird survival, habitat use, and mobility during the post-fledging period. I used radio telemetry to measure the movements of 122 fledglings of four species across the urban gradient of the Seattle metropolitan area from 2003-2005. Mortality of post-fledging birds was low, and land cover effects on survival were limited. I observed more mortality in forested areas than in the urban matrix, and independent juveniles often moved into urban areas without increased risk of death. I found little consistency in habitat use within each species, with the exception of American Robins, who used residential areas more so than forested areas. Migratory species were the most mobile, but juvenile mobility was limited in proportion to the imperviousness of the developed landscape. Parts of the urban matrix were permeable to movement and provided consistent food resources to dispersing juveniles.Because limitation in dispersal of juveniles and adults between years can affect bird population viability, I measured the rates of natal and breeding dispersal, site fidelity, natal philopatry, and dispersal distances of 9 songbird species from 1999-2006. Species, sexes, and age classes differed in their rates of all four movement categories and dispersal distances, which were related to prior breeding success, territory density, and local and landscape forest metrics. I suggest urban growth strategies across multiple scales for maintaining effective bird dispersal in urban ecosystems that focus on maximizing the amount of forest cover and minimizing the amount of impervious urban cover.The incorporation of science into environmental policy is a concern at many levels of decision making. I interviewed planners and consultants who conducted scientific reviews associated with a Washington State Growth Management Act amendment that requires the inclusion of best available science in protecting critical areas. Jurisdictions of different sizes varied in their definition of best available science and how they dealt with conflicting scientific information. They also differed in the types of science they used and the process by which included science in their land-use policies.
- Forestry