The rainbow looks different to a human than it does to a honeybee or a zebra finch. That’s because these animals can see colors that we humans simply can’t. Now scientists have developed a new video recording and analysis technique to better understand how the world looks through the eyes of other species. The accurate and relatively inexpensive method, described in a study published on January 23 in PLOS Biology, is already offering biologists surprising discoveries about the lives of different species.
Humans have three types of cone cells in their eyes. This trio of photoreceptors typically detects red, green and blue wavelengths of light, which combine into millions of distinct colors in the spectrum from 380 to 700 nanometers in wavelength—what we call “visible light.” Some animals, though, can see light with even higher frequencies, called ultraviolet, or UV, light. Most birds have this ability, along with honeybees, reptiles and certain bony fish.
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To capture animal vision on video, Vasas and her colleagues developed a portable 3-D-printed enclosure containing a beam splitter that separates light into UV and the human-visible spectrum. The two streams are captured by two different cameras. One is a standard camera that detects visible-wavelength light, and the other is a modified camera that is sensitive to UV. On its own, the UV-sensitive camera wouldn’t be able to record detailed information on the rest of the light spectrum in a single shot. But paired together, the two cameras can simultaneously record high-quality video that encompasses a wide range of the light spectrum. Then a set of algorithms aligns the two videos and produces versions of the footage that are representative of different animals’ color views, such as those of birds or bees.
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Capturing video in this way “fills a really important gap in our ability to model animal vision,” says Jolyon Troscianko, a visual ecologist at the University of Exeter in England, who wasn’t involved in the new research. He notes that in nature, “a lot of interesting things move,” such as animals that are engaging in mating dances or rapid defense displays. Until now, researchers studying these dynamic behaviors have been stuck with the human perspective.
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The technique is already revealing unseen phenomena of the natural world, she adds: for example, by recording an iridescent peacock feather rotating under a light, the researchers found shifts in color that are even more vibrant to fellow peafowl than they are to humans. Vasas and her colleagues also captured the brief startle display of a black swallowtail caterpillar and saw for the first time that its hornlike defense appendages are UV-reflective.
“None of these things were hypotheses that we had in advance,” Vasas says. Moving forward, “I think it will reveal a lot of things that I can’t yet imagine.”
