Factors that affect the survival of nestling birds can drive the dynamics of populations and the evolution of life histories. Such factors may include a variety of intrinsic, biotic, or abiotic factors that vary in magnitude or effect over ecological time scales. Consequently, estimates of the influence of such factors on nest success may differ when estimated from short- vs. long-term studies. We tested this possibility by estimating the influence of 2 intrinsic factors (female age and inbreeding coefficient), 2 abiotic factors (rainfall and temperature), and 3 biotic factors (breeding density, parasitism rate, and brood parasitism) previously found to predict success (≥1 fledged young) in a 39 yr study of a Song Sparrow (Melospiza melodia) population on Mandarte Island, British Columbia, Canada. We then compared those estimates to others obtained from parallel models based on the the first 13 yr, middle 13 yr, and last 13 yr of the study. Over the entire study, nest success increased in females from ages 1 to 3 yr but declined thereafter. Nest success also declined as female inbreeding, rainfall during nesting, and breeding density increased. We further observed that nests parasitized by Brown-headed Cowbirds (Molothrus ater) or located in areas subject to high parasitism rates failed more often than unparasitized nests or those in areas with fewer parasitized nests. By contrast, the only factors identified as influencing nest success in all three 13 yr study periods examined were female age and population density, whereas the effects of inbreeding, brood parasitism, and rainfall varied temporally. Our results indicate that precise estimates of the effects of intrinsic, abiotic, and biotic drivers on nest success may require long-term studies, particularly for influential factors that occur episodically.