According to the concept of “survival of the fittest," if a population of birds eats worms that they find deep under ground by using their beaks, which members of the bird population would be more fit?

The birds that have beaks better equipped for the task of eating worms under ground. Narrow, sharp and strong beaks would be better at digging through the dirt to find worms. So birds with these types of beaks would be fitter and thus, would survive.