THE EFFECTS OF DISTANCE AND ISOLATION ON SONG-TYPE SHARING IN THE CAROLINA WREN

ABsTRAcr.-I describe the geographic distribution of song types in the Carolina Wren (Thryothorus ludovicianus) in continuous and discontinuous populations along the eastern shore of the Chesapeake Bay and adjacent islands. On average, individuals at the same site held 66% of their songs in common (range = 49.5-89.5%). At sites in continuous mainland populations, I found a negative linear correlation between the distance separating individuals and the percentage of songs shared. Wrens on isolated island sites shared less than 20% of their song types with individuals on the nearest mainland areas. Song sharing among males separated by 3 km of water was equivalent to that found in males separated by 145 km of continuous mainland habitat. Of the 309 song types in the total sample, 78% were restricted to one site. The percentage of songs shared among neighboring free-ranging wrens found in this study is compared to the percentage of undegraded songs learned by naive young males in a laboratory experiment. Received 16 Feb. 1987, accepted 25 May 1987. Many recent studies of the functional significance of song sharing among