Abstract
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.
Highlights
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
An inflection air temperature of 38.0 ± SE 0.6 °C, body temperature increased by 0.5 °C per 1 °C increase in air temperature
The species’ critical thermal maximum is substantially higher than the known avian range (Fig. 2), exceeding by 2–3 °C the values associated with breakdown of respiratory function in poultry[15,16] and the body temperatures associated with loss of motor function in wild b irds[27,28,29,30,40,41]
Summary
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. As part of a study of adaptive variation in avian heat tolerance, we investigated thermoregulation during acute heat exposure in the red-billed quelea (Quelea quelea) This small (18-g) African passerine is widely considered the most abundant non-domesticated bird on Earth, with post-breeding population estimates of ~ 1.5 billion individuals[25]. Under conditions where hydration status potentially varies substantially across individuals within a vast flock, selection should favour the capacity for water conservation via facultative hyperthermia
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