Studies of Darwin's finches have provided some of science's most compelling examples of how natural selection can drive phenotypic change. It was recently discovered that species specialized to feed on hard seeds have a decreased ability to conduct rapid changes in beak gape during singing. In turn, this limits their performance in producing dynamically complex songs. As songs of Darwin's finches are used in species recognition and mate choice, the observed trade-off between force and velocity of the beak may have a direct influence on interspecies mating dynamics, probabilities of hybridization, and ultimately the process of speciation. HOwever, it is unknown what causes this biomechanical trade-off. There are several candidates, such as the inertial properties of the skeletal elements involved, the gearing from the muscles to the upper and lower beak via joints and levers, or the size, orientation and architecture of the different jaw muscles involved. The purpose of the proposed research is to identify the biomechanical basis of this trade-off via dynamic, mutlibody modelling based on a motion analysis of the beak of a species that closely resembles the Darwin's finches (Java finch), and a unique, existing database of 3D reconstructions of the cranial morphology of the Java Finch and several Darwin's finches. This analysis will allow us to quantify the impact of different pathways of morphological change leading to increased biting performance on song dynamics.