Hummingbirds are fascinating creatures that hold many world records:
- The bee hummingbird is the world’s smallest bird, which lays the smallest eggs measuring at 0.275 inches long and weighing 0.0009 ounces.
- The ruby-throated hummingbird has the fastest wing beat in the world at 200 beats per second.
- Hummingbirds are the only birds in the world that can fly upside down and backward.
- They have the highest metabolic rate of any known animal and have to consume at least half their weight in nectar or tiny insects daily to maintain those rates.
- The vervain hummingbird builds the smallest bird nest in the world, at about half the size of a walnut shell.
Now, they can add the lowest body temperature to that list, as they can reach temperatures lower than any non-hibernating mammal and any other bird in the world. Researchers studying six hummingbird species in the Andes have discovered that the body temperature of the black metaltail hummingbird can fall as low as 3.3°C (38°F).
Small creatures, including the hummingbird, certain bats, and many marsupial species, can enter a state known as daily torpor, where they turn down their body temperature and metabolism to conserve energy.
Daily torpor isn’t a prolonged state like hibernation, which for some animals, like groundhogs, can last as long as 150 days. After one night in torpor, the hummingbird’s body temperature rises to around 40°C (104°F) as its metabolic rate increases.
Prof Andrew McKechnie, a co-author of the study, notes that torpor is essential to the survival of hummingbirds during the cold Andean nights. Without it, they would have to burn an immense amount of energy to maintain a body temperature of 40°C (104°F). “They wouldn’t be able to store up enough fat at the end of the day to provide sufficient fuel to last them for the entire night,” he added.
In the study, published in the journal Biology Letters, Prof McKechnie and his team describe how they captured 26 hummingbirds of six different species in Peru, where air temperatures dropped as low as 2.4°C (36°F) at night. They placed the tiny birds in tents without food for at least one night, tracking changes in body temperature and mass.
The team found that 24 out of the 26 birds entered the torpor state; though, their lowest body temperature varied between species and individuals. The black metaltail hummingbird was the winner of the lowest body temperature at 3.3°C (38°F). The time spent in torpor also varied – the black metaltail spent on average 10.6 hours in torpor at night, compared with 5.7 hours for the giant hummingbird. The lower the hummingbird’s body mass, the longer they spent in torpor.
According to McKechnie, further analysis revealed that the differences in torpor between the species were, in part, rooted in evolution. “You have different species using different torpor patterns, despite them all being in common conditions at the same site, experiencing the same weather,” he noted.
There are some gorgeous hummingbirds in Peru, including the ‘Tufted coquette’ found in the Andes, seen in the video below.
