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Animal profile
Rangifer tarandus
Reindeer are the only deer in which both sexes normally grow antlers, and the only ones domesticated at scale, herded across northern Eurasia. Wild populations undertake some of the longest land migrations of any mammal.
Reindeer detect light down to about 320 nanometres, well below the human limit. In snow, which reflects ultraviolet strongly, this turns lichen, urine and wolf fur into dark shapes against a bright field.
The reflective layer behind a reindeer's retina is golden in summer and deep blue by midwinter. The shift scatters more light back through the retina, buying sensitivity in the long polar dusk at the cost of a sharper image.