Which is most likely to account for the large change between years 6 and 8?

Ornithologists conducting surveys deep within the western regions of the Amazon River basin happened upon a group of uniquely colored parrots that expressed a near-fluorescent yellow pigment in their display plumage that clearly set them apart from others in their population, whose dominant color was a much deeper red. These brighter birds were much more conspicuous within the foliage in which they dwelt, and the researchers thought that this might bring a great selection pressure to bear against this variation. The researchers followed this special population every other summer for a total... Show more

Ornithologists conducting surveys deep within the western regions of the Amazon River basin happened upon a group of uniquely colored parrots that expressed a near-fluorescent yellow pigment in their display plumage that clearly set them apart from others in their population, whose dominant color was a much deeper red. These brighter birds were much more conspicuous within the foliage in which they dwelt, and the researchers thought that this might bring a great selection pressure to bear against this variation. The researchers followed this special population every other summer for a total of 10 years. The data they collected during this period are presented below.

PERCENTAGE OF TOTAL POPULATION IN STUDY YEAR 

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