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The Cerulean Warbler (Setophaga cerulea) is a mature forest obligate and one of the fastest declining songbird species in the United States. This decline may be related to a lack of disturbance within contemporary forests; however, the consequences of disturbance on the species have not been rigorously evaluated. Thus, we assessed multiple responses by Cerulean Warblers to a range of experimental forest disturbances across the core of their breeding range in the Appalachian Mountains. We quantified individual and population responses to these manipulations, and assessed the potential consequences of disturbance on the sexual signaling system. Male ceruleans were strongly attracted to intermediate and heavy disturbances at the stand scale. Despite attraction to disturbed habitats, nest success declined in these conditions, particularly in the highly productive Cumberland Mountains of northern Tennessee. Taken together, these opposing responses suggest that anthropogenically-disturbed forests may act as local ecological traps, but the impact of these local traps on the global population is dependent on several unestimated parameters. At a finer scale, selection for habitat features varied spatially. Males consistently selected for territories near canopy gaps and on productive slopes, but they displayed inconsistent territory selection in regards to tree diameter, basal area, overstory canopy cover, and canopy height. Females were more consistent in their selection of features within territories, selecting nest patches with large, well-spaced trees near disturbances. Floristically, female ceruleans consistently selected for sugar maples (Acer saccharum), white oaks (Quercus alba), and cucumber magnolias (Magnolia acuminata) as nest trees and they selected against red maples (A. rubrum) and red oaks (Q. rubra). Disturbances had little effect on male age structure, but males that occupied disturbed forest habitat were in better condition than those in undisturbed habitat. Parental behavior differed among disturbances, with birds in more highly disturbed habitats provisioning their young at greater rates, but bringing smaller food loads, potentially helping to explain the decrease in nest survival in disturbances. Finally, we found that male ceruleans displayed various plumage ornaments that signaled individual quality. However, the relationship between breast band width and body mass was contingent on habitat, and only existed in intermediate disturbances.

Over the past century, populations of North American grassland songbirds have declined sharply as a consequence of habitat destruction. Alberta’s mixed-grass prairie constitutes Canada’s largest remaining tract of native grassland. However, this region has recently undergone a rapid expansion of conventional oil and natural gas development, and few studies have documented its effects on songbird nesting success. During the 2012-2014 breeding seasons, I monitored 813 nests of grassland songbirds located at sites that varied with respect to presence/absence, distance from, and types of oil and gas infrastructure (pump jacks, screw pumps, compressor stations) and gravel roads. Nest survival was significantly lower at infrastructure sites relative to controls for both Savannah sparrow and vesper sparrow. Additionally, vesper sparrow nest density was greater within 100 m of structures. These findings suggest that habitat disturbance caused by infrastructure may result in increased frequencies of nest predation at multiple spatial scales. / February 2016