Structure and function of a complex vocal signal: Duets of the yellow-naped Amazon (Amazona auropalliata)

Mated pairs of yellow-naped amazons (Amazona auropalliata) produce duets, which are coordinated acoustic signals organized by well-defined syntactic rules. Many aspects of duets remained poorly understood, both in yellow-naped amazons and other species. To increase our understanding of duets, I conducted a review of the structure and function of duets in birds, as well as a series of analyses and experiments to investigate several aspects of duets in yellow-naped amazons, including: (i) patterns of variation, (ii) function of duets, and (iii) function of syntax in duets.;In Chapter Two, I examined the structure and function of duets in 46 species of birds. My review confirms that duets are complex signals; duets have multiple functions in most species, and duets are structurally diverse. Chapters Three, Four and Five focus on duets in the yellow-naped amazon. In Chapter Three, I investigated patterns of geographic and structural variation in duets within one dialect In Chapter Four, I investigated the function of duets by conducting a playback experiment with three treatments: normal duets, and two types of manipulated 'monets' consisting of just the male notes or just the female notes. In Chapter Five, I tested the hypothesis that duet syntax is critical for duet function with a playback experiment in which I presented birds with playbacks of normal duets and duets with broken syntax (one of the syntactic rules was artificially broken).;The structure of yellow-naped amazon duets vary at multiple levels of social organization and in every aspect of structure that I examined; this variation may allow duets to function in an array of contexts. Pairs responded aggressively and in a coordinated manner to playbacks of normal duets as well as manipulated duets such as monets and duets with broken syntax. High levels of coordination between pair members indicate that duets are cooperative, while aggressiveness indicates that duets are critical for territory maintenance and defense. Although pairs responded to all treatments, slight decreases in response to manipulated playbacks (i.e. monets and broken duets) as compared to normal playbacks for some variables indicated that including: (i) patterns of variation, (ii) function of duets, and (iii) function of syntax in duets.;In Chapter Two, I examined the structure and function of duets in 46 species of birds. My review confirms that duets are complex signals; duets have multiple functions in most species, and duets are structurally diverse Chapters Three, Four and Five focus on duets in the yellow-naped amazon. In Chapter Three, I investigated patterns of geographic and structural variation in duets within one dialect. In Chapter Four, I investigated the function of duets by conducting a playback experiment with three treatments: normal duets, and two types of manipulated 'monets' consisting of just the male notes or just the female notes. In Chapter Five, I tested the hypothesis that duet syntax is critical for duet function with a playback experiment in which I presented birds with playbacks of normal duets and duets with broken syntax (one of the syntactic rules was artificially broken).;The structure of yellow-naped amazon duets vary at multiple levels of social organization and in every aspect of structure that I examined; this variation may allow duets to function in an array of contexts. Pairs responded aggressively and in a coordinated manner to playbacks of normal duets as well as manipulated duets such as monets and duets with broken syntax. High levels of coordination between pair members indicate that duets are cooperative, while aggressiveness indicates that duets are critical for territory maintenance and defense. Although pairs responded to all treatments, slight decreases in response to manipulated playbacks (i.e. monets and broken duets) as compared to normal playbacks for some variables indicated that pairs recognize the differences between treatments, and that those duets features may be important to function.