USE OF 2 SINGING MODES BY HOODED WARBLERS AS ADAPTATIONS FOR SIGNALING

Hooded warblers Wilsonia citrina use two modes of singing, repeat mode (one pattern sung repeatedly) and mixed mode (2-4 other patterns sung in irregular sequence). Intensive focal-individual sampling of 14 mal es documented the use of these modes of singing throughout the nesting cycle. Males of different ages (first breeding season or later) did n ot differ in use of the two modes. Time spent singing in repeat mode d ecreased markedly after acquiring a mate, but time spent singing mixed mode did not change significantly across stages of the nesting cycle. Males sang more when their neighbors sang at a distance of 25 m or mo re. Repeat mode increased in this situation before a male acquired a m ate, while mixed mode increased afterwards. Near a neighbor (within 25 m), males avoided use of repeat mode. Nearby females before the onset of incubation evoked increased use of repeat mode. More distant, call ing females elicited little response before incubation, but thereafter calling females tended to suppress all singing. Males used mixed mode proportionately more in locations nearer neighbors. There were no ind ications that variation in singing influenced the dates on which males acquired mates. Unmated males late in the breeding season sang persis tently in repeat mode, even more than eventually mated males had early in the season before they acquired mates. These results provide suppo rt, with some reservations, for three hypotheses for the evolution of distinct modes of singing: (1) specializations for male and female lis teners; (2) specializations for indicating conditional behavioral tend encies; and (3) specializations for communication in low- and high-noi se situations. These hypotheses are not mutually exclusive, and all th ree in combination might offer the strongest explanation for the evolu tion of distinct singing modes in this species and other paruline warb lers.