An island experiences a decade long drought which causes a die off of several plant species. The only plants that survive have extremely small seeds with less nutritional value. Parrots which live on the island and eat seeds are more likely to survive and successfully reproduce if they are smaller since smaller body size requires less calories. Over the course of the decade, the average body size of the parrot population decreases. Which of the following statements below are correct?

a. The parrot population has evolved.
b. This is an example of genetic drift.
c. This is an example of directional selection.
d. This population meets the conditions for the Hardy Weinberg equilibrium.
e. This is an example of stabilizing selection.
f. This is an example of natural selection.