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Fur properties play a critical role in the thermoregulation of mammals and are becoming of particular interest as the frequency, intensity, and duration of extreme heat events are increasing under climate change. Australian flying-foxes are known to experience mass die-offs during extreme heat events, yet little is known about how different fur properties affect their thermoregulatory needs. In this study, we examined the differences and patterns in fur properties among and within the four mainland Australian flying-fox species: Pteropus poliocephalus , P. alecto , P. conspicillatus , and P. scapulatus. Using museum specimens, we collected data on fur solar reflectance, fur length and fur depth from the four species across their distribution. We found that P. poliocephalus had significantly longer and deeper fur, and P. alecto had significantly lower fur solar reflectivity, compared with the other species. Across all species, juveniles had deeper fur than adults, and females of P. alecto and P. conspicillatus had deeper fur than males. The biophysical effects of these fur properties are complex and contingent on the degree of exposure to solar radiation, but they may help to explain the relatively higher mortality of P. alecto and of juveniles and females that is commonly observed during extreme heat events. The variation in fur properties of flying-foxes can help us understand why there are differences in survival rates among different species, sexes, and ages during extreme heat events. We found that there were distinct differences in the length, depth, and solar reflectance of fur among different species and demographics, which can cause differences in the experienced heat load. Thus, understanding exactly how interactions between fur properties affect heat transfer can help us explain the higher mortality of some species and demographics. Photo by Himali Ratnayake. [ABSTRACT FROM AUTHOR]