Life-History Variation and Demography in Western Bluebirds (Sialia Mexicana) in Oregon

Abstract

Abstract During the seven-year period from 1995 to 2001, we conducted a detailed, demographic study of a population of Western Bluebirds (Sialia mexicana) in Oregon. Using a data set consisting of individual capture histories for ≈8,000 birds, we estimated age-specific and study-year specific survival estimates of adult males and females. High juvenile recruitment enabled us to generate accurate estimates of juvenile survival from fledging to first breeding attempt. We analyzed fecundity patterns, including nesting phenology, clutch success, and overall reproductive success for nearly 1,200 nesting attempts. Temporal variation in survival and fecundity had strong demographic consequences. Asymptotic population growth analysis suggested a slowly growing population. However, variation in vital rates led to population declines even over the relative short timescale of our study, making the conservation status of this species uncertain. In addition to those results, we discuss the costs and benefits of using data collected by volunteers to study demographic processes.