A population of birds, with various size beaks, eats seeds….

A population of birds, with various size beaks, eats seeds. Small seeds can be eaten by birds with small beaks. Larger, thicker seeds can only be eaten by birds with larger, thicker beaks. There is a shortage of small seeds but that there are still many large seeds. Natural selection will change the population of birds such that birds with larger beaks will survive and produce off springs and birds will small beaks will not be able to survive. What type of natural selection is described here?