Activities of 29 male Cerulean Warblers (Setophaga cerulea) were quantified on two sites in West Virginia during May–June 2005. Singing and foraging were the most common of 11 observed behavioral activities (81.6%), while maintenance and mating behaviors were uncommonly observed. Male activity differed among vegetative strata (P = 0.02) with lower- and mid-canopy strata used most often (70% of observations), especially for foraging, perching, and preening. The upper-canopy was used primarily for singing, particularly within core areas of territories and in association with canopy gaps. Foraging occurred more than expected outside of core areas. Males were associated with canopy gaps during 30% of observations, but the distribution of behavioral activities was not significantly related (P = 0.06) to gap presence. Males used 23 different tree species for a variety of activities with oaks (Quercus spp.) used most often on the xeric site and black cherry (Prunus serotina) and black locust (Robinia pseudoacacia) on the mesic site. Tree species used for singing differed between core and non-core areas (P < 0.0001) but distribution of singing and foraging activity did not differ among tree species (P = 0.13). Cerulean Warblers appear to be flexible in use of tree species. Their use of different canopy strata for different behavioral activities provides an explanation for the affinity this species exhibits for a vertically stratified forest canopy.
