Conservation of Cerulean Warblers Requires Both Dense and Gappy Forest Habitat
In birds, the period between fledglings living in nests and independence from parents remains poorly understood, despite being a critical time in the life cycle when most mortality occurs. Cerulean warblers (Setophaga cerulea), a migratory species of extremely high conservation concern, nest in mature deciduous forests; range-wide conservation efforts have focused on maintaining or creating quality nesting habitat. A scientist from the USDA Forest Service's Northern Research Station and his partners used radio-tracking of cerulean fledglings to better understand habitat selection during the dependent post-fledging period. They found fledgling habitat selection to be dynamic, varying with fledgling age. Compared to nesting habitat, recent fledglings selected areas with greater sapling cover and less stand basal area. As fledglings matured, they selected areas further from canopy gaps and with greater mid-story cover. Overall, fledglings used areas with smaller and more numerous trees, fewer canopy gaps, and greater mid-story cover than found in nesting habitat. Based on these results, management focused solely on maintaining quality nesting habitat is likely to prove inadequate to recover the species. This research suggests forest management that creates heterogeneous landscapes, including both mature stands with numerous canopy gaps as well as younger stands with a dense mid-story, are needed to effectively conserve cerulean warblers.