Reindeer and the quest for Scottish enlichenment

Abstract

In the hall of animal oddities, the reindeer ( Rangifer tarandus) is the only mammal with a color-shifting tapetum lucidum and the only ruminant with a lichen-dominated diet. These puzzling traits coexist with yet another enigma––ocular media that transmit up to 60% of ultraviolet (UV) light, enough to excite the cones responsible for color vision. It is unclear why any day-active circum-Arctic mammal would benefit from UV visual sensitivity, but it could improve detection of UV-absorbing lichens against a background of UV-reflecting snows, especially during the extended twilight hours of winter. To explore this idea and advance our understanding of reindeer visual ecology, we recorded the reflectance spectra of several ground-growing (terricolous), shrubby (fruticose) lichens in the diets of reindeer living in Cairngorms National Park, Scotland.

A Review of Cervidae Visual Ecology

“…Cervids may use their ability to distinguish color at certain wavelengths to identify preferred food items. Surface vegetation, including lichen, appear in high achromatic contrast against snow in ultraviolet-only images [72,117]. Given the sensitivity of caribou/reindeer to ultraviolet wavelengths [68], they likely experience improved forage discrimination in their ultraviolet-dominated light environments [72,117].…”

“…Surface vegetation, including lichen, appear in high achromatic contrast against snow in ultraviolet-only images [72,117]. Given the sensitivity of caribou/reindeer to ultraviolet wavelengths [68], they likely experience improved forage discrimination in their ultraviolet-dominated light environments [72,117]. Many fungi and plants emit or reflect ultraviolet cues [118,119], and ultraviolet sensitivity might play a role in fine-scale forage discrimination for cervids.…”