The forest will be shining – at least for the deer
The rubbing of deer antlers and hoof scratches alter how parts of the forest reflect short-wavelength light, perhaps leaving a glowing signal.
Deer signposts may become extra reflective in the twilight.
Stan Techiela Author/Naturalist/Wildlife Photographer/Getty Images
At dawn and dusk, forests often appear muted and almost monochromatic to the human eye. But white-tailed deer may see a very different landscape: To them, the forest may be sparkling.
Since the 1970s, biologists have understood that deer leave signposts for scent-based communication – places where they have rubbed their antlers on trees or left urine on the ground that they scratch with their hooves. But a group of researchers wondered whether these marks also provide visual messages.
Researchers scanned and analyzed 146 such signposts in Whitehall Forest in the state of Georgia using ultraviolet light. He found that although the signposts appear unremarkable in daylight, They emit a blue-green light that deer can see When exposed to ultraviolet wavelengths in the morning and evening. This may be because the antlers rub away the bark, exposing lignin-rich inner wood that transmits longer wavelengths in a way that bark does not.
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“If someone has seen a reflector on a tree, the rub is similar to that – although obviously not as pronounced,” says study co-author Daniel DeRose-Brockaert, a biologist at the University of Georgia.
As the breeding season approaches, the visual contrasts intensify. Their study describing the findings has been published Ecology and Evolution, The authors argue that these latter marks are brighter because the male deer’s antlers have fully hardened and their rubbing can expose more interior wood. Increased glandular activity with increasing testosterone may also add incidental organic residues to the surface.
The authors say this change in light is particularly relevant, because white-tailed deer’s eyes have increased sensitivity to short- and medium-wavelength colors, especially in low light conditions.
Traditionally, mammalian biofluorescence, e.g. Shining fur in bare-nosed wombats and bandicootsHas been studied as a property of the animal. biological materials such as Semen also fluoresces under UV light. This work suggests that biofluorescence may also be embedded in the environment, even if only subtly – adding a largely overlooked layer to the way animals communicate.
However, not everyone is convinced that these fluorescent contrasts would be visible to deer under natural conditions. “If humans don’t see these marks under natural light, deer are unlikely to see them either,” says ecologist Almut Kelber of Lund University in Sweden, who was not part of the study. She says that demonstrating a visual role would require behavioral tests that distinguish vision from smell.
DeRose-Brockaert describes the study as a first step – it documents that rubs and scrapes can produce contrast at wavelengths that deer can see and lays the groundwork for future experiments with natural lighting.
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