Animal Behavior/Darwin's Finches

The Galapagos Islands finches have been used by Charles Darwin and many other scientist to study how “ random variation and natural selection can drive the production of organisms with novel features, adapted to new ways of life" (Alberts 2004). The finches studied in the Galapagos Island are usually characterized by the great variance in beaks and the function of beaks. The finches beaks were first thought to change over many years because of local ecological condition, but many scientists devised a new hypothesis which stated, “As a consequence of beak evolution, there have been changes in the structure if finch vocal signals (Podos 2004).” This hypothesis was based the assumption that beaks have a direct correlation in effecting song production. The Galapagos Island finches displayed a wide variety phenotypes of beaks with different forms and functions caused by natural selection over many years. This phenotype variation was hypothesized by the Grants to be a result of natural selection because of ecological conditions. The new studies, however, tested to see if finch beaks have an effect on the acoustic structure of the songbird songs. The first experiment done to test this hypothesis involved first checking to see if beak movement caused sound production, which turned out to be true. Thus, one could imply that beak variations could cause a different song production. The goal of these researches is “ to show how research on the relationship between beaks and song is providing novel insights into the interplay of morphological adaptation and the evolution communication signals" (Podos 2004). The bird song is actually made in the birds syrinx, which is similar to the human larynx during speech production. The scientist then addressed the question of how the birds are able to send pure tonal signals across such a long range and distance. The answer is that the birds are able to change their vocal tracts configurations, which in turn directly changes the frequency of their songs. The three generalizations, which these finches fall into describing their songs are, simple, variability, and cross-species overlap. If the beak is opened more wide then it creates a higher pitched sound. So it could be hypothesized that a large beaked bird will have a large vocal tract and will in turn create a lower song frequency. This hypothesis was backed up by the studies of Maria Palacious and Pablo Tubaro who tested the Neotropical Woodcreepers Pendrocolaptinae, which produced lower frequency songs with long beaks. These scientists tested, these highly protected finches, by video taping them and then determining the beak gapes for each song for the different finches. The two main reason male finches use their singing, like many other singing birds, is for territory defense and mate attraction, but the difference in beak size could affect both these characteristics, because some males with either small or large beaks could not produce the right song in other to perform these tasks. This lead Nowick and colleagues to test to see if a beak changed its size for food collection, then would this have a direct affect on how fast or slow a finch could move its beak to produce its specific song. Nowick then concluded that there was a positive correlation between “divergences of beaks and its influence not only the feeding but also their singing behavior.” The scientist, however, plan to broaden their investigation by studying how wider beaks may influence songs and also study other birds with beak morphology such as the crossbills or the Hawaiian honeycreepers.

Works cited

Alberts, B., D. Bray, K. Hopkin, A. Johnson, J. Leiws, M. Raff, K. Roberts, and P. Walter. Essential Cell Biology. New York: Garland Science 27: 7

Podos, Jeffrey, and Stephen Nowicki. " Beaks, adaption, and vocal evolution Darwin's finches." Bioscience 54 (2004): 501-510