Minimum Annual Survival Estimates of Male Cerulean Warblers (Setophaga cerulea) In Southwestern Michigan

Abstract

The Cerulean Warbler (Setophaga cerulea) is a North American landbird showing a high rate of population decline. Estimates of its annual adult survival rate are needed to evaluate its current population status. Annual return rates of 104 color-banded adult male Cerulean Warblers were used to estimate minimum annual survival from 2008–2011. The study site was a large oak-hickory forest bordered by a mosaic of forest tracts and agricultural land in southwestern Michigan. Cormack-Jolly-Seber (CJS) live recapture models yielded an annual survival estimate (Φ) of 0.59. This estimate lies in the range of available CJS survival estimates for other Neotropical migratory species with different population trajectories. In addition, this survival value confirms sink population status for Cerulean Warbler breeding populations studied at widespread locations in the breeding range (all λ < 1.0). Inter-year breeding dispersal was frequently <1.0 km, but seven banded males made breeding dispersal movements among years >1.0 km. Previous studies have suggested that some adult male Cerulean Warblers make very long-distance breeding dispersal movements among years, suggesting realized annual survival rates are higher than reported. The annual adult male survival rate reported here is similar to the only other value obtained from a breeding population of this species. In aggregate, these findings suggest that reduced breeding ground productivity is a probable cause of the long-term population decline of the Cerulean Warbler. Conservation efforts focused on this imperiled songbird species might focus on increasing this demographic factor, perhaps via reforestation of the breeding grounds.