Hummingbirds can drop their body temperature below 40°F when they rest to save energy for the next day
- Hummingbirds use a process called torpor to lower body temperature at night
- This process allows the animal to conserve as much energy as possible
- Sees heart rate slow down from 1,000 to 50 beats per minute
- Researchers studied six Andead hummingbird species and found temperatures plunge from around 40°C in the day to as low as 3.26°C during torpor
Hummingbirds can cool their bodies to less than 4°C (40°F) at night – the lowest temperature recorded in any bird – to save energy for use the daytime, researchers have found.
This rare ability is called torpor, and is a brief hibernation-like state which slashes energy expenditure by 95 per cent in the diminutive birds.
Hummingbirds have wings that beat more than ten times a second and during daylight they use their hovering ability to suck nectar from thousands of flowers.
To keep up, their tiny hearts beat around 1,000 times a minute, but this drops to just 50 during torpor.
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Depending on species, the hummingbirds entered torpor for between two and 13 hours, the researchers write in their study, published in the journal Biology Letters . One species, the black metaltail (pictured), reached the lowest temperature of 3.26°C
The frigid internal temperature at night allows the tiny birds to prepare for the big day ahead.
Researchers from the University of New Mexico looked at 26 hummingbirds from six different species living in the Peruvian Andes.
These birds survive at altitudes of up to 13,000ft (4,000m) and researchers trapped them and inserted a small temperature probe into their rear while they rested.
Researchers recorded the core body temperature throughout the evening and compared that to the outdoor temperature, which could drop as low as 2°C (35F).
Depending on species, the hummingbirds entered torpor for between two and 13 hours, the researchers write in their study, published in the journal Biology Letters.
The species in torpor for the shortest period of time was the giant hummingbird, while the longest was the black metaltail.
The black metaltail also reached the lowest temperature of all individuals in the study, with academics recording it as low as 3.26°C (37.8F).
‘You’d think they’re frozen,’ lead author Professor Blair Wolf told New Scientist. ‘They feel like a cold rock.’
The birds exit torpor around sunrise and their body temperature soars at a rate of 1°C a minute until they’re back to their normal temperature of about 40°C (104F).
This rapid warming uses lots of energy up, but the amount the birds save outweighs this cost, the researchers say.
By weighing the birds as they slept, the academics also found that the birds which were in torpor for longer lost less weight, therefore indicating they saved more energy.
Torpor is a process used by very few species as it greatly increases the risk of predation.
For the hummingbirds found in the Andes, this is of little concern as there are very few predators at that altitude.
Other animals that employ the daily hibernation strategy include night hawks, lemurs and hamsters.
The species in torpor for the shortest period of time was the giant hummingbird (pictured), while the longest was the black metaltail