Evolution and Vocal Communication in Darwin's Finches

Field research on Darwin's finches of the Galápagos Islands, Ecuador, aims to document interconnections between behavior (feeding, singing), morphology (beaks, heads, body size), and evolutionary divergence. Darwin's finches are a well-known example of adaptive radiation, in which a single ancestral species gave rise to multiple and diverse descendent species. The Darwin's finch radiation has featured, most famously, pronounced diversification of beak form and function, represented at its extremes by the thin probing beaks of warbler finches and the massive seed-crushing beaks of large ground finches.

My field team and I -- including key collaborators Andrew Hendry, Sarah Huber, Anthony Herrel, and Luis Fernande de Leon -- have been exploring a number of questions about finch behavior, morphology, and evolution, particularly for birds on the central Galápagos island of Santa Cruz. Some of our work focuses on relationships between beak morphological diversification, vocal proficieny and song structure. Interconnections between beaks and vocal proficiency are predicted given recent evidence that beak movements play a key role in song production. Video analysis of birds singing in the field has revealed that Darwin's finches, like other songbirds, adjust beak gape in precise register with changes in song frequencies. Gape changes are thought to occur to help Darwin's finches and other songbirds to maintain the pure-tonal quality of their songs as they vary in frequency. This observation leads to the prediction that birds adapted for greater crushing strength should suffer greater constraints on vocal proficiency, because of mechanical tradeoffs between force and speed. Inter and intraspecific analysis of song structure in relation to beak morphology support this prediction. We are also examining the potential impact of correlated evolution between beaks and song on the process of reproductive isolation. Song playback studies are being conducted to evaluate the impact of song variation on song function. We are conducting observations of intraspecific mate choice, in order to assess possibilities of sympatric population divergence. Other current field activities include (i) observational studies of feeding in relation to beak form and function; (ii) tests of bite force capacities; and (iii) documentation of variation in genetic, morphological, and vocal traits among birds on Santa Cruz Island. We have been fortunate to receive generous support for this work from the National Science Foundation. Check out the splash page for NSF's Division of Integrative Organismal Systems website. The photo shows one of our finches, JP1046, enjoying a Scutia berry.

Sexual selection and mating displays in blue-black grassquits.

A recently-initiated collaboration with Regina Macedo and her research group at the University of Brasilia (UnB) examines communication behavior and signal function in blue-black grassquits, at a cerrado site in south-central Brazil. During the breeding season, males of this species produce repetitive, multimodal "leap" displays, in order to maintain territories and attract mates. Our project aims to quantify variation among males in a number of display parameters, in order to assess if and how these parameters correlate with male quality, and if and how display parameters influence mating success. This project is receiving generous support from the National Science Foundation.

Additional research projects in Brazil, largely in collaboration with researchers from the Instituto Nacional de Pesquisas da Amazônia (INPA) in Manaus, Brasil, aim to document patterns of communication and ecology in various neotropical vertebrate taxa. A collaboration with Vera M. F. da Silva and Marcos Rossi-Santos examines the structure of vocalizations in the two species of Amazon river dolphins, Sotalia fluviatilis (the tucuxi) and Inia geoffrensis (the boto). Another set of projects, spearheaded by Cristina Cox Fernandes, aims to document spatial variation in the richness and abundance of electric fishes (Gymnotiformes) across the Amazon river basin, and also to understand relationships between morphology, hormones, and properties of their electric organ discharges.

Vocal learning, evolution, and performance in North American sparrrows. Songbird songs are wonderfully diverse, not only across species but also within species, populations, and individuals. The evolution of this diversity is linked to the fact that most songbirds learn their songs. They require exposure to song models during a critical phase in their first year of life, and subsequently engage in a protracted period of motor development before being able to produce crystallized song. Vocal features that are shaped during learning will be retained over evolutionary time through cultural transmission.

My collaborators and I are interested in understanding how proximate features of song production and perception, as expressed during development, can shape patterns of song learning and diversification. This work follows directly from the pioneering studies of Peter Marler and Susan Peters in the 1970s at Rockefeller University. One of our specific interests in song learning is that it can provide a unique empirical window into the role of performance in behavioral evolution, given songbirds' natural predisposition for producing accurate copies of song models. Research in collaboration with Steve Nowicki and Susan Peters of Duke University has examined how the coordination of beak and syrinx movements during development can both impose constraints upon and provide opportunities for novel timing patterns in song production. At UMass, David Lahti, Dana Moseley, and I have been conducting a series of experiments to further examine the influence of trill rate on song development. Questions about vocal diversification are also addressed using quantitative surveys of vocal diversity, using bioacoustic analyses. Ongoing work focuses on performance-based tradeoffs between acoustic features in trilled segments of sparrow songs. Local field work in Massachusetts provides complementary perspectives on song diversity and function.

Swallow tailed gull, San Cristobal Island, Galapagos