Under these drastically changing conditions, the struggle to survive favored the larger birds with deep, strong beaks for opening the hard seeds. Smaller finches with less-powerful beaks perished.

A bird beak is the most important resource it has, and every species has one solely designed for survival. Birds use beaks for just about everything: building nests, feeding their young ...

There was even a flighted top predator, the white-tailed sea eagle, which snagged baby moa-nalos and any other birds it could get ... Natural selection reshaped the beaks of pioneer finches ...