Red-feathered and blue-feathered birds occupy the same environment. The birds with the red feathers are better able to survive and avoid predators. This means that the population of red-feathered birds will increase in future generations. This illustrates the process of

Natural selection.

Explanation:

Natural selection is the process in which the well suited organism is selected by the nature which is able to survive the environmental conditions while on the other hand, not well suited organisms are extinct from the environment. Due to this natural selection, the population of red-feathered birds will increase in the future as compared to blue-feathered birds which will be decreases due to susceptible to predators and environment.