Ethology zyxwvutsrq 74, zyxwvutsrqpo 265-284 (1987) zyxwvuts 0 1987 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0179-1613 Biology Department, McGill University, Montreal zyx Song Repertoires of American Warblers (Parulinae): Honest Advertising or Assessment? R. E. LEMON, S. MONETTE zyxw & D. ROFF With 8 zyxwvut figures Received: December 2, 1985 Accepted: September 28, 1986 (G. M. Burghardt) Abstract We consider a number of hypotheses explaining the social use of song repertoires by territory- holding of male American warblers (Parulinae). Males vary by species in having from one to several songs that are used in station singing. In the latter case the songs are clustered into subsets or modes. The songs (= modes) vary in use by season and territorial position. Much of the organization appears to reflect a duality of function relative to mate attraction on the one hand and to interaction between males on the other. We focus especially on two hypotheses of male interaction that appear to make opposite and testable predictions, these being whether the males use the songs to honestly advertise their claims on the territory, or whether they are assessing their relative resource-holding potentials. Introduction At the centre of functional studies of bird song is the question of why birds have song repertoires and why these vary so much in size across species as well as individuals. Since song is used in the context of reproduction, especially among territorial birds, functional interpretations are focused on sexual selection, either as a basis for advertising male quality to females or to competing males (e.g. LEMON 1968; HOWARD 1974; KREBS et al. 1978; SMITH et a]. 1978; CATCHPOLE 1980; SLATER 1981). Studies of American warblers have traditionally recognised this duality of function both based on observed differences in use of repertoire items by season and by territorial position (FICKEN & FICKEN 1965; MORSE 1970; LEIN 1972,1978, KROODSMA 1981). U.S. Copyright Clearance Cenrer Code Statement: 01 79-161 3/87/7404-0265$02.50/0