Perhaps you may wish to update your scientific repertoire just a tad, for Peter and Rosemary Grant of Princeton University have been studying medium ground finches (Geospiza fortis) on Daphne Major in the Galapagos Islands for over 20 years and have well-documented evidence of beak-depth evolution due to environmental pressures. I suggest you perform a Google Search for further details of their work and results.
Acutally you are totally mischaracterizing the findings of the Grants - as have evolutionists for the last 20 years or so. First of all, the finches are not different species, they can intermarry and produce offspring which are even more viable than those of the same variety. Secondly, yes the beaks of the finches can grow and also get smaller. However, this happens according to the rainfall and goes back and forth according to it. It is not evolution, it is adaptation and the fact that the beaks change within a short time to small, large, then small again shows it is not due to any mutation which is what is required by evolution.