Nest Survival of Western Bluebirds Using Tree Cavities in Managed Ponderosa Pine Forests of Central Washington

Abstract

Abstract. We examined the association of temporal and spatial factors with nest survival of Western Bluebirds (Sialia mexicana) nesting in tree cavities in ponderosa pine (Pinus ponderosa) forests along the east slope of the Cascade Mountains, Washington. All study areas were managed for timber production through planned harvests or postfire salvage logging. Bluebirds laid a mean clutch of 5.3 ± 0.1 (SE) eggs (n = 131), and successful nests fledged an average of 4.5 ± 0.2 young (n = 85). Using a model-selection framework, we found that nest survival was a function of clutch size and treatment and that there was a quadratic effect of nest age. Daily survival rates decreased after the onset of incubation, then increased through the nestling period, and were higher for clutches with ≥5 eggs and in stands that were burned and salvaged. Survivorship over the entire period for clutches (n = 131 nests) with ≤4, 5, and ≥6 eggs was 0.39 (95% CI: 0.11, 0.65), 0.61 (95% CI: 0.34, 0.80), and 0.71 (95% CI: 0.46, 0.85)...