Proposed research examines the structure, function, and evolution of communication displays in a tropical songbird species, the blue-black grassquit. This project will be conducted and supervised by three core collaborators: Dr. Regina Macedo (University of Brasilia, Brazil), Dr. Jefferson Graves (University of St. Andrews, Scotland) and the PI. Field work will focus on grassquit "leap displays" at a field site in Brasilia, Brazil. The main goals of field work are to characterize variation among males in display traits, to identify the mechanistic bases of display variation, and to characterize how females use display trait variation in mate choice. Mating displays will be characterized using optical spectrophotometry, high-speed videography, and focal and automated audio recording. It is hypothesized that males showing high performance in some display traits (e.g. leap height) will express deficits in others (e.g., leap rate), because of mechanistic, energetic, or allocation-based constraints. The impact of display trait variation on female choice will be documented using genetic paternity analysis. It is hypothesized that females will choose mates based largely on behavioral display traits, because such traits should provide particularly reliable indicators of male health, status, and quality. This project includes training of Brazilian and American students in evolutionary biology, animal behavior, and ornithology, and includes several planned exchange courses. A broader goal of our plan is to facilitate interchange between researchers from the three countries, with special interest in fostering interactions between Brazilian and US scientific communities.
This project examines patterns and functions of animal communication displays. Our project has focused on the blue-black grassquit, a species of songbird in which males court females using complex aerial displays (see figure). Genetic and behavioral data were collected at a field site in the Cerrado grassland habitat of central Brazil. Our goals have been to: (1) characterize, for the first time, the complex mating displays ("leap displays") of the blue-black grassquit; (2) document how individuals vary in their abilities to execute these displays; (3) assess redundancies and tradeoffs among multiple display features, both within and across signaling modalities (motor, visual, acoustic); (4) link display attributes to variation among individuals in condition, parasite loads, and reproductive success; and (5) explore the communicative value of different signal attributes, using both descriptive and experimental approaches. Descriptive approaches include analysis of genetic variation and assignment of paternity, and experimental approaches include playback studies on the function of both vocal and visual signal components. Our analyses to date have so far led to three main conclusions. First, our analyses suggest that birds have difficulty executing complex displays, which leads to trade-offs among display traits. For example, as birds produce more displays, the complexity of each individual display appears to decline. This suggests a tradeoff between signalling quality and quantity. Second, we find that birds vary widely in their skill as displayers. Some males are able to outperform others in terms of the height and duration of "leaps" within their displays, and in the duration of their calls. Third, our genetic and behavioral data suggest that females prefer to mate with males who excel in the expression of suites of display traits, especially in terms of the height and duration of display leaps. This suggests that displays provide females with reliable indicators of male quality. Ongoing analyses aim to compare the signal value of static ornamental traits (such as feather color) versus dynamic behavioral display traits (such as leap display properties), and to describe in more detail how display traits map onto patterns of mating and male body condition. Data emerging from this project are providing new insights into how mating signals mediate female mate preferences. Our project has involved partnerships between scientists from the US, Brazil, and Scotland. Faculty and docotral students from the US and Brazil have conducted reciprocal visits to each others laboratories, offering training and gaining new experiences in topics in ornithology, behaivor, natural history, and evolutionary biollogy. The collaborative partnership has resulted in numerous papers and conference presentations, with more to come in upcoming years as data analyses are finalized.
