THE ROLE OF CHIP CALLS IN WINTER TERRITORIALITY OF YELLOW WARBLERS

The role of chip calls in the winter territoriality of Yellow Warblers (Dendroica petechia) was studied in the Republic of Panama. There was extensive variation through the day in chip rates and time spent chip ping, with vocalizations greatest in the morning (0630-0830 h) and at dusk (1730-1830 h). A bout of rapid chipping at dusk was observed in s everal birds. Individuals responded aggressively to playbacks of chip calls by increasing chip rate and flying close to playback speakers. Y ellow Warblers responded significantly more aggressively to chip calls of conspecifics than those of a control (Northern Waterthrush, Seiuru s noveboracensis). Results suggest that Yellow Warbler chip vocalizati ons function in defense of winter territories. The role of the conspic uous dusk chipping bout remains to be determined.