Video: Infrared movies capture hummingbirds shedding heat in flight

Hummingbirds are impressive flyers, managing 12 meters and 50 wingbeats per second. But all that flapping could put them in danger of overheating. Research published online today in Royal Society Open Science shows that they use their unfeathered regions, particularly their feet and eyes, to regulate body temperature during flight. Scientists used infrared thermal imaging to measure heat dissipation from calliope hummingbirds (Selasphorus calliope) flying in a wind tunnel (shown above). They identified hotspots under the wings, on the feet, and around the eyes, which were at least 8°C warmer than the rest of the body. The birds rely on different hot spots to regulate body temperature when flying at different speeds. Hummingbirds actually find it hardest to maintain a constant temperature when flying slowly, because there is less airflow to keep them cool. At lower speeds, they trebled the size of their eye hot spot and dangled their feet below their bodies to maximize heat loss. The researchers estimated the birds’ heat budget, and found that at speeds of 0 m/s to 12 m/s, they lost enough heat from these hot spots to maintain a safe body temperature. But they note the challenge of keeping cool may become harder as the climate warms.

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