JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. We compared responses of males whose mates were fertile or nonfertile with differences in song structure (SRS vs. LRS and soft LRS), amplitude (SRS and soft LRS vs. LRS), and tempo (slow SRS vs. fast SRS). Males responded more strongly to SRS than to LRS or soft LRS, indicating that song structure had a greater effect on response than song amplitude. SRS tempo did not detectably affect male response. Importantly, males responded more strongly to SRS when their mates were fertile, presumably because hearing SRS can indicate that a male's mate is being courted by an intruding male and a strong response can deter extrapair competitors. We conclude that lowamplitude songs can function in both inter-and intrasexual communication and should receive greater attention in future studies of mate choice and male-male competition.

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Complex displays play an important role in female mate choice and male-male interactions for many species. Displays used in both inter-and intrasexual interactions offer an opportunity to examine how the ordering and structure of complex displays may vary with context. To understand how social context can influence the performance of complex displays, we investigated the predictability of display elements across displays in the presence and absence of females. The lance-tailed manakin, Chiroxiphia lanceolata, is a small lekking bird that performs complex, acrobatic displays. Pairs of alpha and beta males cooperatively display for females, but they also perform very similar displays in the absence of females. We quantified the performance of individual alpha and beta males within the dual-male display and the joint performance of the two males using Shannon's information entropy, and compared these values to understand how male display predictability varies with social context. Differences were assessed using generalized linear mixed models to account for repeated measures of male pairs. Predictability of individual performance within the dual-male interaction did not differ with female presence; however, entropy metrics describing the interaction of the alpha and beta male indicated that displays for females were more predictable and coordinated. This study provides a quantitative assessment of display element performance across different social contexts of female presence and absence, and suggests that the dual-male phenotype may be an important factor in female mate choice for cooperatively displaying species.