A few years ago, Norwegian and British researchers discovered that one part of a reindeer’s eye changes color in winter in order to increase the sensitivity of its vision. During summer, its eyes are a golden color; during winter, they change to blue (perhaps giving them an edge for spotting predators).
Scientists studying a different herd found that light pollution kept its habitat dimly lit and never truly dark. As a result, the eyes of these reindeer cannot shift fully to blue and will actually turn green. This disruption in the natural processes can adversely affect the reindeers’ behavior and lead to problems with reproduction, adaptation and survival.