Maybe This Can Help you i Guess
Differences in sparrow bill length are due to adaptation and natural selection. Individuals with the "best" size bill will be most successful in acquiring resources from their environment. Sparrows with 10 mm long bill size will be more successful at crushing seeds and pass the traits on to offspring for similar-sized bills. Those individuals with larger and smaller beak sizes will not be as successful in acquiring resources and will pass on fewer traits for bill size. In order for natural selection to work, there must be a variation of traits. Individuals with the "best" variation to crack seeds will be selected over time because they have adapted to the environment.
