ACOUSTICAL FEATURES OF SONG CATEGORIES OF THE ADELAIDE WARBLER (DENDROICA-ADELAIDAE)

I identified acoustical features that distinguish the two song categor ies, A and B, of the Adelaide's Warbler (Dendroica adelaidae). Like ma ny other wood-warbler species, male Adelaide's Warblers have functiona lly structured song repertoires such that A and B song categories are distinguished by common usage among males. The particular song types u sed in a given category, however, vary greatly among individual males. Therefore, I focused my analysis on acoustical features other than so ng types. Song categories were distinguished by three major features: (1) the sound energy within a given B song was concentrated into a nar rower frequency band, which was shifted about 600 Hz lower than for A songs; (2) the structure of B songs tended to be more complex, as they contained more note types and greater contrast between successive typ es than did A songs (discriminant function analysis using structural a nd frequency data correctly classified 85% of songs to category); and (3) the singing behavior associated with B-song sequences was more com plex, due to inclusion of a larger number of song types, more frequent switching or alternating between them, and a more rapid rate of song delivery. Overall, the B category appears to represent a more complex and lower frequency signal than the A category. Differences between th e two song categories, which parallel data available for other parulin e species, should reduce signal ambiguity and are consistent with seve ral nonmutually exclusive functional interpretations: The B-song categ ory, used in intrasexual interactions, might represent a more aggressi ve signal or might be specialized for carrying motivational informatio n. Females might find the higher-frequency A-song category more appeas ing or stimulating. Song categories A and B also might be specialized for traveling different distances, at different times of day, or throu gh different microhabitats.