Defense strategies against environmental heat stress in birds

When heat-acclimated pigeons are exposed to ambient temperatures of 50-60"C, extremely high cutaneous evaporative cooling, together with a high insulative capacity of the feather coat, creates for the bird a microclimate within which physiological processes can be regulated normally. By skillfully using this cooling garment, pigeons maintain their resting metabolic rate and regulate low skin and body temperatures, employing neither panting nor gular fluttering. These physiological achievements parallel those of arctic animals. Hence, during animal evolution towards inhabiting extreme thermal environments, selection seems to have favored adaptations at the lowest energy cost in both the extreme cold arctic and the hottest deserts of the world.