When it gets cold at night, one hummingbird survives by nearly freezing stiff and letting its body temperature dive.

Iran Press/America: The high Andes of Peru are a hummingbird’s paradise. There are few predators. And wildflowers cover the mountain slopes. Their blooms are full of the sugary nectar these birds need for energy. But there’s one problem. At night, temperatures dip below freezing. Now scientists have uncovered the strategy these birds use to make it through those cold nights: They chill out.

As the sun goes down and it gets cold, these hummingbirds land for the night. Then they enter torpor, a state of suspended animation. They no longer move. Their heart rate slows way down. And their body temperature dives. One species, the black metaltail (Metallura phoebe), chills to 3.26° Celsius (37.8° Fahrenheit), the new study shows, according to Science News for Students.

That’s the coldest body temperature ever recorded in a bird or non-hibernating mammal.

Keeping warm at night takes energy. As endothermic animals, mammals and birds fuel their body heat with food. This lets them stay active when it’s cooler outside. But some of that heat gets lost through the skin. And small critters lose a bigger share of that heat. Their small bodies also mean they can’t generate heat as quickly as bigger animals.

Being super-small, hummingbirds may weigh only about six grams — about as much as a US quarter. To fuel their flights, a hummingbird needs nectar from 500 flowers a day. So they don’t waste energy on trying to stay warm all night. 

Cooling to near-death temperatures lets these hummers save precious energy. The next day they still have enough to take flight again and feed.

By day, the birds’ tiny-yet-mighty hearts can beat 1,200 times a minute. But during torpor, that rate plummets to as few as 40 beats a minute. 

Around sunrise, hummingbirds start revving up again. By vibrating their muscles, the birds warm about one degree a minute. 


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