Reflection of near-infrared light confers thermal protection in birds

• Published in: Nature communications 2018-09, Vol.9 (1), p.3610-7, Article 3610
• Main Authors: Medina, Iliana, Newton, Elizabeth, Kearney, Michael R., Mulder, Raoul A., Porter, Warren P., Stuart-Fox, Devi
• Format: Article
• Language: English
• Subjects: 631/158/857; 631/181/757; 631/601/1737; Adaptation, Biological; Animals; Arid environments; Aridity; Australia; Biophysical Phenomena; Birds; Birds - physiology; Body mass; Body Size; Climate; Deserts; Ecosystem; Energy; Evaporative cooling; Female; Heat; Heating; Humanities and Social Sciences; I.R. radiation; Infrared reflection; Light reflection; Male; Males; Models, Biological; multidisciplinary; Phylogenetics; Phylogeny; Reflectance; Science; Science (multidisciplinary); Solar radiation; Species; Sunlight; Thermal protection; Ultraviolet radiation; Water loss; Wavelengths
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-05898-8

Biologists have focused their attention on the optical functions of light reflected at ultraviolet and human-visible wavelengths. However, most radiant energy in sunlight occurs in ‘unseen’ near-infrared (NIR) wavelengths. The capacity to reflect solar radiation at NIR wavelengths may enable animals to control heat gain and remain within their critical thermal limits. Here, using a continent-wide phylogenetic analysis of Australian birds, we show that species occupying hot, arid environments reflect more radiant energy in NIR wavelengths than species in thermally benign environments, even when controlling for variation in visible colour. Biophysical models confirm that smaller species gain a greater advantage from high NIR reflectivity in hot, arid environments, reducing water loss from compensatory evaporative cooling by up to 2% body mass per hour. These results highlight the importance of NIR reflectivity for thermal protection, which may become increasingly critical as the frequency of extreme climatic events increases. More than half of solar radiation is at near-infrared (NIR) wavelengths. Here, Medina et al. show that among Australian birds NIR reflectivity is higher in species from hot, arid environments and their biophysical modelling further shows that this can reduce water loss from evaporative cooling.