Life history, demography, and individual variation in western bluebirds
Keyser, Amber Jessen
MetadataShow full item record
Effective conservation management of threatened populations depends upon quality demographic data analyzed in a robust statistical framework and long-term monitoring to determine the efficacy of management strategies. In this study, I assessed the conservation status of a threatened population of western bluebirds (Sialia mexicana) in northwestern Oregon. The focal population has been on a slow recovery from precipitous population declines in the mid-20 th century. Using a detailed demographic analysis that included both age-related and annual variation in vital rates, I showed that the population, under current conditions, is nearly stable and perhaps slightly increasing. A subset of the population was the subject of a supplemental feeding experiment. By following individuals throughout their lifetimes, I found that providing extra food to nestlings had positive short-term effects but caused severe decreases in future fecundity. The strong, contradictory effects on fitness components led me to conclude that under some conditions, supplemental feeding could lead to population decline, but that if implemented with care, supplemental feeding could be a useful conservation strategy. These results suggest that the future prospects for the population are encouraging. However, during the course of the study, I documented an infectious outbreak in the population, which caused high mortality. There was clear evidence for the action of natural selection on morphology and plumage. This episode of high mortality emphasized the precarious state of the population in the face of changing conditions at the rural-urban interface.