The Remarkable Temperature Regulation of Hummingbirds

Living in the high Andes, hummingbirds face extreme cold temperatures by employing a unique temperature-regulation mechanism. Recent research has uncovered the secret behind this fascinating adaptation.

Hummingbirds have the highest metabolic rate relative to body weight among vertebrates, approximately 77 times higher than that of humans. This necessitates almost constant feeding to sustain their energy levels. When it is too dark or cold outside to find food, hummingbirds risk energy depletion due to their rapid energy consumption.

However, nature has equipped hummingbirds with a special adaptation to cope with cold environments, especially at high altitudes like the Andes in South America.

A recent study by researchers from the University of New Mexico has revealed that hummingbirds have an extraordinary ability to lower their body temperature. They can decrease their body temperature by 10 to 30°C and maintain this reduced temperature for several hours.

During this period, the birds are nearly motionless. “You might even think the birds are dead until you touch them,” said Blair Wolf, a biologist from the University of New Mexico.

As temperatures rise with the arrival of daylight or warmer external conditions, the hummingbirds’ body temperature gradually returns to normal. Wolf suggests that this mechanism is similar to hibernation observed in some mammals.

By reducing their body temperature, hummingbirds significantly slow down their metabolism, reducing the risk of starvation due to energy loss.

Typically, a hummingbird’s heart beats between 1,000 and 1,200 times per minute. During torpor, their heart rate drops to just 50 beats per minute.

Since March 2015, Blair Wolf’s research team has been studying hummingbirds in the Andes at elevations exceeding 3,800 meters, where nighttime temperatures can drop close to freezing.

The team captured 26 hummingbirds from six different species, including Patagona gigas, the largest hummingbird species. They placed the birds in separate sleeping areas and used a metal probe inserted into their cloaca to measure their body temperature.

The research revealed that not only do hummingbirds lower their body temperature, but some species can reduce it by several tens of degrees. For example, the Metallura phoebe hummingbird can lower its temperature to below 3.3°C, the lowest body temperature recorded in birds and non-hibernating mammals.

On cold nights, hummingbirds typically reduce their body temperature to about 5-10°C, which is approximately 26°C lower than their normal active temperature.

“This is a remarkable ability,” said Anusha Shankar, an ecologist at Cornell University’s Laboratory of Ornithology, who was not involved in the study. One reason Shankar finds this so impressive is that most bird species are endothermic, meaning their body temperature usually remains relatively constant. In contrast, humans face significant risks when their body temperature drops by just 2°C.