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.