Why were the species of finches different on each island?

Generally these different species because of their different feeding and nesting habits do not interbreed. In a series of dry seasons the differences in beak size increases causing further separation of the different types of finches

Generally these different species because of their different feeding and nesting habits do not interbreed. In a series of dry seasons the differences in beak size increases causing further separation of the different types of finches.

Explanation:

x would be the most and the least would be y because there are more fruit   and seeds than flock z has insects