To survive frigid nights, hummingbirds cool themselves to record-low temperatures
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 temperaturesometimes as much as 33°Cfor hours at a time, new research suggests.
Its a capacity thats 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 wouldnt even know it was alive if you picked it up, Wolf says. But when the morning comes and its time to feed, he says, the birds quickly warm themselves back up again. Its like hibernation but regulated on an even tighter schedule. [snip]