Darwin's Finches Sing a Song about Food
The classical example of evolutionary diversification, Darwin's finches, is in the news again.  Jeff Podos, our new behavioral ecologist, has just published evidence in the journal Nature in which he identifies a possible cause for the rapid evolution of both vocalization and species diversity in Darwin's finches.  Jeff was awarded an NSF grant to study these phenomena.  He is taking annual field trips to the Galapagos to gather data to test his theories.
Jeff's research equipment includes audio and video recorders which allow him to simultaneously capture the vocalizations and behavior of his target species.  To test his hypotheses, Jeff analyzes behavior, beak morphology, and vocalizations.  Experiments include the playing of high quality male vocalizations to a female to see how she responds.
The audio recordings of bird song are transformed into sonograms which are plots of time, frequency, and intensity of songs.  The remarkable finding is that, in eight species of Darwin's finches, certain aspects of vocalization are related to variation in beak structure (see sonograms at right for Geospiza fortis (upper) and Certhidea olivacea (lower) abstracted from his Nature illustration).  Food availability could be a driving force for changes in beak structure which might lead to behavioral isolation via mating incompatibilities.  Thus, two powerful interacting forces, feeding and communication at the time of mating, could be the causative agents of rapid speciation.
Furthermore, in a number of species of Darwin's finches, beak structure has been shown to vary from generation to generation, depending on the types of available food.  This adds credence to Podos' theories of interplay between beak shape and communication.  Could the changes in food types over protracted time intervals result in the selection of beak shapes that preclude vocalizations once successful in attracting mates?  This might select for species with a more variable song repertoire.  In Jeff's hands, Darwin's finches have once again become a laboratory for the study of evolution.