Why is the bird's beak shorter on Darwin Island? (scientific questions)

The result of environmental directional selection. There should have been birds with long beaks and short beaks on this island, because after a lot of wind and rain, seeds are generally scraped to the ground, leaving few seeds on plants. Birds that feed easily from the ground (short-billed birds) are more likely to survive, while long-billed birds are much less likely to survive. As time goes on, the number of beaked birds gradually decreases and disappears. It is often short-billed birds that stay on this island.