Studies performed in humans and farm animals indicate that infrared thermography can be used to estimate the body temperature of homeotherms. However, this method has seldom been validated for wild animals in their natural environment. To fill this major gap, we shot facial infrared thermograms of red-footed boobies ( Sula sula ) in situ, while remotely recording their internal body temperatures. We identified strong linear relationships between the surface temperatures of six facial regions and the internal body temperatures of the birds. At the individual level, maximum facial temperatures, corresponding to the corner of the bill and the internal cantus of the eye, provided the best relationships with internal temperatures. At the species level, minimal and mean temperatures of the eyeballs provided the best estimates of internal temperatures. Wind speed, ambient temperature, sun exposure and shooting distance influenced bird facial surface temperatures as inferred through infrared thermography. Our study underlines the practicability of using facial infrared thermography to infer avian body temperatures, and opens new perspectives for the conservation physiology of wild species.