For the finches, body size and the size and shape of their beaks are traits that vary in adapting to environmental niches or changes in those niches. ... Under these drastically changing conditions, the struggle to survive favored the larger birds with deep, strong beaks for opening the hard seeds.They started out with beaks good for seeds then went off into leaves, insects, fruit, and grubs. All finches adapted to their island and brought up the reproduction rate since they weren't all fighting for the same food. ... The finches beaks adapted to the food source which was favored by natural selection
