Spatial variation in habitat selection by cerulean warblers

The cerulean warbler is a small, canopy-foraging bird that often is associated during the breeding season with older hardwood forests in the eastern United States and southern Canada. It winters in the northern Andes Mountains of Venezuela, Colombia, Ecuador, Peru, and Bolivia.

Since 1966, counts of cerulean warblers have declined in the U.S. Fish & Wildlife Service’s Breeding Bird Survey and many ornithologists have expressed concerns about the status and population trends of this species. 

To answer questions about potential relationships between forest management and cerulean warblers, NCASI recently helped coordinate a series of activities by the Cerulean Warbler Conservation Initiative, a large research partnership designed to address information needs related to this species. The Initiative included a large-scale habitat experiment in the core of the species’ range in the Appalachian Mountains that included a no-harvest control and three harvesting treatments that reduced pre-treatment basal area by 20%, 40%, or 75%. These treatments were replicated on seven study areas in Ohio, Kentucky, Tennessee, and West Virginia.

Selected results from the experiment have been published in an article titled “Spatial variation in breeding habitat selection by cerulean warblers (Setophaga cerulea) throughout the Appalachian Mountains” (The Auk 130(1):46−59) by T.J. Boves et al. Co-authors include Dr. Ben Wigley with NCASI. The abstract follows.

“Studies of habitat selection are often of limited utility because they focus on small geographic areas, fail to examine behavior at multiple scales, or lack an assessment of the fitness consequences of habitat decisions. These limitations can hamper the identification of successful site-specific management strategies, which are urgently needed for severely declining species like Cerulean Warblers (Setophaga cerulea). We assessed how breeding habitat decisions made by Cerulean Warblers at multiple scales, and the subsequent effects of these decisions on nest survival, varied across the Appalachian Mountains. Selection for structural habitat features varied substantially among areas, particularly at the territory scale. Males within the least-forested landscapes selected microhabitat features that reflected more closed-canopy forest conditions, whereas males in highly forested landscapes favored features associated with canopy disturbance. Selection of nest-patch and nest-site attributes by females was more consistent across areas, with females selecting for increased tree size and understory cover and decreased basal area and midstory cover. Floristic preferences were similar across study areas: White Oak (Quercus alba), Cucumber-tree (Magnolia acuminata), and Sugar Maple (Acer saccharum) were preferred as nest trees, whereas red oak species (subgenus Erythrobalanus) and Red Maple (A. rubrum) were avoided. The habitat features that were related to nest survival also varied among study areas, and preferred features were negatively associated with nest survival at one area. Thus, our results indicate that large-scale spatial heterogeneity may influence local habitat-selection behavior and that it may be necessary to articulate site-specific management strategies for Cerulean Warblers.”

  

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