A small population of a specific bird species lives on an island in the Pacific Ocean. All of the birds of this species have a crest of feathers on their heads. The color of the crest can be orange, yellow, or white. An individual's crest color does not effect its chance of survival or its reproductive success. A hurricane hits the island and all of the birds with orange crests are killed, as well as many of the individuals with yellow and white crests. This causes the gene for orange crests to be lost from the population. The loss of the gene coding for an orange crest in the bird population described above is an example of _______.