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The colours that we see are a result of the light reflected within a narrow range of wavelengths – what we call the visible spectrum. But sunlight also spans wavelengths that we cannot see. But there’s one set of wavelengths that elude all of us – these are near infra-red (NIR) wavelengths. And understanding how bird feathers interact with these wavelengths is important, not just for birds, but also for humans through the potential for improvements in thermal efficiency. Our research in the School of BioSciences at the University of Melbourne suggests that some Australian birds can control their temperature and avoid overheating by reflecting near-infrared wavelengths of sunlight. We collected information on 90 species of Australian birds and found a very strong link between living in hot, arid regions and reflecting a higher proportion of near-infrared light. Researchers in the field of animal colouration have largely ignored near-infrared light, because it isn’t easy to measure and there’s no evidence that animals can see these wavelengths. Because these wavelengths are invisible, they don’t affect camouflage or sexual attractiveness, which are very important in the animal world. This means that many animals can control their temperature by altering reflection of near-infrared light without compromising their ability to hide or attract a mate.