The thermal tolerances of vertebrates are generally restricted to body temperatures below
45–47 °C, and avian and mammalian critical thermal maxima seldom exceed 46 °C. We investigated
thermoregulation at high air temperatures in the red-billed quelea (Quelea quelea), an African
passerine bird that occurs in flocks sometimes numbering millions of individuals. Our data reveal
this species can increase its body temperature to extremely high levels: queleas exposed to air
temperature > 45 °C increased body temperature to 48.0 ± 0.7 °C without any apparent ill-effect, with
individual values as high as 49.1 °C. These values exceed known avian lethal limits, with tolerance of
body temperature > 48 °C unprecedented among birds and mammals.