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The Coolest Hummingbird, as Measured by an Actual Thermometer

By Marc Devokaitis
Black Metaltail by Arthur Grosse/Macaulay Library.t
Black Metaltail by Arthur Grosse/Macaulay Library.
From the Winter 2021 issue of Living Bird magazine. Subscribe now.

Black Metaltail. The name seems fit for a hard-hitting rock band, but this bird’s cool factor goes way beyond its heavy-metal moniker.

Research published in Biology Letters in September revealed that the Black Metaltail—a hummingbird that lives at high elevations in the Peruvian Andes—is able to lower its nighttime body temperature to an astounding 3.3°C (38°F), the lowest body temperature ever recorded in any bird.

Scientists discovered this new bird superlative when monitoring the body temperature of hummingbirds spending the night at near-freezing temps, 10,000 feet up on a tropical mountain. All six species they monitored in the study—and 24 of 26 individuals—entered torpor, a temporary state of greatly reduced metabolism and body temperature that many hummingbirds use to conserve energy when air temperatures plunge.

But one Black Metaltail’s capacity for torpor took the prize, its body temperature plunging to just 1°C above the surrounding air temperature.

Based on their observations, the researchers concluded that this diminutive hummer might have the capacity to lower its internal temp even more, writing that the metaltail “showed no evidence of maintaining a setpoint [body temperature] at even the lowest [air temperature] encountered.” They even speculated that the metaltail and other hummers capable of deep torpor might be able to hibernate during sustained cold weather.

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American Kestrel by Blair Dudeck / Macaulay Library

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