To survive frigid nights, hummingbirds cool themselves to record-low temperatures [View all]

[Backseat Driver]

https://www.sciencemag.org/news/2020/09/survive-frigid-nights-hummingbirds-cool-themselves-record-low-temperatures

High in the Andes, thousands of meters above sea level, speedy hummingbirds defy near-freezing temperatures. These tiny flyers endure the cold with a counterintuitive trick: They lower their body temperature—sometimes as much as 33°C—for hours at a time, new research suggests.

“It’s a capacity that’s just incredible,” says Anusha Shankar, a physiological ecologist at the Cornell Lab of Ornithology, who was not involved with the study.

Among vertebrates, hummingbirds have the highest metabolism for their size. With a metabolic rate roughly 77 times that of an average human, they need to feed nearly continuously. But when it gets too cold or dark to forage, maintaining a normal body temperature is energetically draining. Instead, the small animals can cool their internal temperature by 10°C to 30°C. This slows their metabolism by as much as 95% and protects them from starvation, says Blair Wolf, a physiological ecologist at the University of New Mexico, Albuquerque.

In this state, called torpor, a bird is motionless and unresponsive. “You wouldn’t even know it was alive if you picked it up,” Wolf says. But when the morning comes and it’s time to feed, he says, the birds quickly warm themselves back up again. “It’s like hibernation but regulated on an even tighter schedule.” [snip]