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Acoustic signals are ubiquitous across mammalian taxa. They serve a myriad of functions related to the formation and maintenance of social bonds and can provide conspecifics information about caller condition, motivation and identity. Disentangling the relative importance of evolutionary mechanisms that shape vocal variation is difficult, and little is known about heritability of mammalian vocalizations. Duetting--coordinated vocalizations within male and female pairs--arose independently at least four times across the Primate Order. Primate duets contain individual- or pair-level signatures, but the mechanisms that shape this variation remain unclear. Here, we test for evidence of heritability in two call types (pulses and chirps) from the duets of captive coppery titi monkeys (Plecturocebus cupreus). We extracted four features--note rate, duration, minimum and maximum fundamental frequency--from spectrograms of pulses and chirps, and estimated heritability of the features. We also tested whether features varied with sex or body weight. We found evidence for moderate heritability in one of the features examined (chirp note rate), whereas inter-individual variance was the most important source of variance for the rest of the features. We did not find evidence for sex differences in any of the features, but we did find that body weight and fundamental frequency of chirp elements covaried. Kin recognition has been invoked as a possible explanation for heritability or kin signatures in mammalian vocalizations. Although the function of primate duets remains a topic of debate, the presence of moderate heritability in titi monkey chirp elements indicates duets may serve a kin recognition function.

Neotropical bird species provide exceptional opportunities for advancing the understanding of avian communication systems. This dissertation focuses on the singing behavior of the White-breasted Wood Wren (Henicorhina leucosticta), which is not well understood even though it expresses behaviors such as female song and duetting that are at the forefront of research in avian communication. I present the background in this area of research and make the case that this species is of special interest to the study of avian communication because of its phylogenetic relationship to other duetting wrens and because its singing style is not easily categorized by singing behavior of other duetting species. In Chapter 2, I characterize the repertoire and singing behavior of this species and show that male repertoires are larger than those of females and can be classified into three groups based on spectral characteristics and song use. I describe unique high-frequency ‘introductory notes’ that directly precede songs within a bout but are facultatively included with the songs. In Chapter 3, I discuss playback experiments that suggest introductory notes act as a graded signal in certain song types during countersinging interactions. Differences in threat salience between four common song types was identified with one song type in particular that provoked lower song rates from subjects and was never song matched. These results suggest a separate function of this song type and together emphasize the potential role of structural cues in regulating singing interactions. In Chapter 4, I assess potential functions of duetting with two-speaker playback experiments and utilize a microphone sensor array developed at UCLA to localize the vocalizations of individuals. I show that in opposition to the mate-guarding hypothesis, the threat of unmated same sex intruders (solo playback) was not greater than the threat posed by paired intruders (duet playback). This supports territorial defense as

Neotropical bird species provide exceptional opportunities for advancing the understanding of avian communication systems. This dissertation focuses on the singing behavior of the White-breasted Wood Wren (Henicorhina leucosticta), which is not well understood even though it expresses behaviors such as female song and duetting that are at the forefront of research in avian communication. I present the background in this area of research and make the case that this species is of special interest to the study of avian communication because of its phylogenetic relationship to other duetting wrens and because its singing style is not easily categorized by singing behavior of other duetting species. In Chapter 2, I characterize the repertoire and singing behavior of this species and show that male repertoires are larger than those of females and can be classified into three groups based on spectral characteristics and song use. I describe unique high-frequency ‘introductory notes’ that directly precede songs within a bout but are facultatively included with the songs. In Chapter 3, I discuss playback experiments that suggest introductory notes act as a graded signal in certain song types during countersinging interactions. Differences in threat salience between four common song types was identified with one song type in particular that provoked lower song rates from subjects and was never song matched. These results suggest a separate function of this song type and together emphasize the potential role of structural cues in regulating singing interactions. In Chapter 4, I assess potential functions of duetting with two-speaker playback experiments and utilize a microphone sensor array developed at UCLA to localize the vocalizations of individuals. I show that in opposition to the mate-guarding hypothesis, the threat of unmated same sex intruders (solo playback) was not greater than the threat posed by paired intruders (duet playback). This supports territorial defense as