ARE URBAN SPOTTED TOWHEE POPULATIONS SELF-SUSTAINING?
Bartos Smith, S., Portland State University, Portland, United States, sbsmith@pdx.edu; McKay, J.E., Portland State University, Portland, United States, jenmackay34@yahoo.com; Murphy, M, T, Portland State University, Portland, United States, murphym@pdx.edu We have conducted intensive demographic studies of a color banded population of Spotted Towhees (Pipilo maculatus) in 6 greenspaces (range: 1 to 24 ha) within the urban growth boundary in Portland, Oregon, since 2004. Our goal has been to determine whether the local populations breeding in urban habitat fragments are self-sustaining (i.e. source populations; λ ≥ 1) or if they can only be maintained by immigration from outside sources (i.e. sink populations; λ < 1). Preliminary analyses based on two years of data suggest that parks ≤ 10 ha are sinks, while larger parks (>15 hectares) are sources. Towhees are multi-brooded and seasonal productivity/female did not differ among parks of different sizes, but apparent adult survival was si
