Demography of sooty fox sparrows following a shift from a migratory to resident life history

Identifying causes and consequences of variation in species life history has the potential to improve predictions about how climate and land use change may affect the demography and distribution of species in future. Sooty fox sparrows (Passerella unalaschcensis J.F. Gmelin, 1789; or commonly grouped within Passerella iliaca B. Merrem, 1786) were migrants that rarely bred in the Georgia Basin of British Columbia prior to ~1950 but have since established resident populations. Data on 270 color-banded birds and 54 nests on Mandarte Is., BC, allowed us to estimate demographic vital rates and population growth in one recently established population. Annual fecundity (F), estimated as the product of the number of broods initiated (1.5 ± 0.01; mean ± sd), clutch size (2.82 ± 0.44), and probability of survival to fledging (0.68 ± 0.02), exceeded values reported for migrants, supporting the hypothesis that residents invest more in reproduction on average than migrants within species. Estimating juvenile and adult overwinter survival (Sj = 0.32 ± 0.06, and Sa = 0.69 ± 0.05) next allowed us to simulate an expected distribution of population growth rates as: λexp = Sa + (Sj × F), given parameter error. Our estimate of λexp (1.61 ± 0.57) implies expeditious population growth, consistent with the species’ recent colonization of the region.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author