Within-territory habitat use and microhabitat selection by male cerulean warblers (Dendroica cerulea)

Although most habitat characteristics are known to be continuously variable in space, practicality dictates that most habitat-selection studies at the spatial scale of the territory treat within-territory habitat as essentially homogeneous. However, the limitations associated with such a compromise have remained largely unexamined. Male Cerulean Warblers (Dendroica cerulea) exhibit nonrandom space- use patterns within their territories, in that all territories contain areas of intensive use or core areas. In addition to documenting territory-wide habitat and behavioral use patterns in this species, we asked two specific questions about core-area structure and function. (1) Are core-area habitats distinct in their vegetative composition and structure from the rest of the territory? (2) What behavioral mechanisms underlie the nonrandom space-use patterns? On a territory-wide basis, males used trees in proportion to their availability; however, core areas were predominantly composed of bitternut hickory (Carya cordiformis), which was a highly preferred song-post tree. Core areas were not consistently associated with any other habitat feature, including canopy gaps. Core areas were singing centers; song-post densities within core areas were 10× higher than in noncore areas. In our study area, bitternut hickories have significant delayed leaf-out patterns, potentially offering minimal acoustic hindrance to song transmission until late in the breeding season. These singing centers may be strategically placed to simultaneously maintain vigilance over social nests and maximize communication with conspecifics. Core areas are potentially as important to males as nesting habitat is to females, and their provision should be taken into account when implementing conservation or management strategies.