Vulture, thermogram. A thermogram shows variation in temperature on the surface of an object, measured by the long-wave infrared radiation it emits. The temperature scale is colour-coded and runs from dark blue (coldest, 2.1 degrees Celsius) through green, yellow and red to white (warmest, 31 degrees Celsius). Feathers prevent heat loss from the bird's body. The head is uncovered to prevent it being fouled when it scavenges flesh, and thus appears hotter.