Appendages in zoo-housed animals: application of thermal imaging to study the thermal state of wildlife under human care.

The present review aims to discuss the application of infrared thermography as a non-invasive tool in wildlife species under human care to determine the role of uninsulated appendages such as horns, antlers, ossicones, casques, beak/bill, proboscis, and legs in animals' thermoregulation. Currently, thermal imaging in the ocular and auricular surfaces of zoo-housed species is used to evaluate the physical and mental state of animals. However, zoos house a wide diversity of animals with highly vascularized appendages, for which infrared thermography research is limited. This review will also describe and analyze the anatomical characteristics of each appendage to establish if they can serve as thermal windows according to the species. For example, bovid horns, antlers, ossicones, beaks/bills, and elephant tusks might be considered thermal windows that reflect vasomotor changes. In contrast, the rhinoceros horn is devoid of blood vessels, where vasodilation or vasoconstriction cannot be evaluated using infrared thermography. Moreover, structures such as the elephant trunk and pinna, and avian and mammal legs have shown environmental influences on the surface temperature. Future studies on zoo-housed animals are required to accurately determine their association with the thermal state and even with clinical conditions in wildlife under human care.