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We studied the use of song types and their acoustic features in different social contexts in the banded wren (Thryothorus pleurostictus), a resident tropical songbird in which males possess about 20 distinctive song types varying in duration, bandwidth, note composition, and trill structure. We recorded six focal males intensively for four days each while we observed context information such as during versus after dawn chorus, presence of the female, counter-versus solo-singing, location at the edge versus centre of the territory, and proximity to the nest. All males used at least some song types differentially during each of these pairs of alternative contexts. Males also preferentially used the song types they shared with a given neighbour when interacting with that bird. Songs delivered during dawn chorus were significantly longer, wider in bandwidth, often compound (double songs), and more likely to contain a rattle or buzz and an up-sweeping trill, compared to songs delivered after dawn chorus. Similar features were also more commonly observed when birds were engaged in intense male-male interactions and boundary disputes after dawn chorus, especially when countersinging at the edge of the territory. The presence of the female caused the male to deliver song types with narrower whole-song and trill bandwidth and fewer rattles and buzzes, and songtype diversity and fraction of compound songs were higher when the female was present. Thus, in addition to using type matching and variations in song-type switching and diversity to signal different levels of aggressive intention, male banded wrens also select song types based on their acoustic structure in different social contexts.In approximately 75% of oscine songbird species, male singers possess repertoires of two or more distinct song types acquired by innovation or imitative learning (MacDougall-Shackleton 1997). Some studies have suggested that each song type conveys the same message and that the primary function of song types is to increase stimulus diversity, reduce habituation of the receiver, and/or relieve stress on syringeal muscles (Nottebohm 1972;Hartshorne 1973;Krebs et al. 1978;Searcy et al. 1982;Lambrechts & Dhondt 1988;Searcy 1992). However, studies on a growing number of species indicate that song types are used selectively in different contexts and therefore probably convey different messages (reviewed in Catchpole and Slater 1995).Context-specific use of song types was first described in the wood warblers (Parulinae), where males were found to possess two acoustically distinct categories of song types apparently specialized for use in intersexual versus intrasexual communication (reviewed in Spector 1992). Type I songs are sung during daylight, relatively slowly, and when near females or by unmated males, suggesting a mate attraction function. Type II songs are sung rapidly in a dawn bout and later in the day during encounters with rival males or while close to territory boundaries, suggesting a territorial function. These associati...

Although males often display from mixed-species aggregations, the influence of nearby heterospecifics on risks associated with sexual signalling has not been previously examined. We tested whether predation and parasitism risks depend on proximity to heterospecific signallers. Using field playback experiments with calls of two species that often display from the same ponds, tú ngara frogs and hourglass treefrogs, we tested two hypotheses: (1) calling near heterospecific signallers attractive to eavesdroppers results in increased attention from predatory bats and parasitic midges (collateral damage hypothesis) or (2) calling near heterospecific signallers reduces an individual's predation and parasitism risks, as eavesdroppers are drawn to the heterospecifics (shadow of safety hypothesis). Bat visitation was not affected by calling neighbours. The number of frog-biting midges attracted to hourglass treefrog calls, however, rose threefold when played near tú ngara calls, supporting the collateral damage hypothesis. We thus show that proximity to heterospecific signallers can drastically alter both the absolute risks of signalling and the relative strengths of pressures from predation and parasitism. Through these mechanisms, interactions between heterospecific guild members are likely to influence the evolution of signalling strategies and the distribution of species at both local and larger scales.