Avian community and microhabitat associations of Cerulean Warblers in Alabama
Cerulean Warblers (Dendroica cerulea) have experienced one of the highest population declines of any neotropical-Nearctic migratory species in North America. We performed point counts and habitat assessments in areas used and unused by Cerulean Warblers in northern Alabama during the 2005 and 2006 breeding seasons to examine their avian associations and identify microhabitat features that best explained their occurrence. We detected on average ~50 Cerulean Warbler males (total) in three disjunct populations during each breeding season. Areas used by Cerulean Warblers were characterized by avian communities with significantly higher species richness, diversity, and abundance compared to areas where they were not detected. Correspondence analysis related Cerulean Warblers to inhabitants of riparian, bottomland deciduous forests (e.g., Kentucky Warbler [Oporornis formosus], Acadian Flycatcher [Empidonax virescens], and Northern Parula [Parula americana]) and two edge specialists (Blue-winged Warbler [Vermivora cyanoptera] and Indigo Bunting [Passerina cyanea]) suggesting Cerulean Warblers in our study areas may be tolerant of some habitat disturbance within an otherwise largely forested landscape. Information theoretic criteria and canonical correspondence analysis indicated Cerulean Warblers preferred bottomland forests containing tall (> 29 m), large diameter, well-spaced (> 27 m2/ha) deciduous trees with greater canopy cover (= 90%), closer (< 20 m) canopy gaps, fewer snags (= 25/ha), and a moderately complex canopy structure.