Infrared Video Shows Hummingbirds Shedding Heat in Flight

January 5, 2016 | Joanne Kennell

Photo credit: Science Magazine

Scientists have figured out why these birds do not overheat.

Did you know hummingbirds flap their wings 50 to 70 times per second?  I find it hard to even imagine something moving that fast.  If it were possible for us to move that quickly, we would probably get really hot and risk overheating.  So why do hummingbirds not face the same fate?

Research recently published in the Royal Society Open Science shows that hummingbirds use their unfeathered regions — mainly their eyes and feet — to regulate body temperature.  The scientists who conducted the study used infrared thermal imaging to measure the heat loss from calliope hummingbirds (Selasphorus calliope) flying in a wind tunnel (shown in the above video).

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There are obvious hot spots seen in the video under the bird’s wings, around the eyes, and on their feet — all of which are at least 14 degrees Fahrenheit (8 degrees Celsius) warmer than the rest of the body.  It turns out hummingbirds rely on different hot spots to regulate their body temperature depending on the speed at which they are flying.

For example, if hummingbirds are flying slowly, they increase the amount of heat escape around their eye hot spot by three times and dangle their feet below their bodies to maximize heat loss.  Surprisingly, hummingbirds find it hardest to regulate body temperature when they are flying slowly because there is less air flowing over their eyes and wings to keep them cool.  

The researchers also estimated the hummingbirds’ heat budget, and found that while traveling at speeds between 0 and 27 miles per hour, they lose enough heat from these hot spots to maintain a safe and healthy body temperature.  However, the scientists warn that keeping cool may become more challenging for hummingbirds as the climate warms.

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