The high Andes mountains of Peru are a hummingbird’s paradise, rich in wildflower nectar and low in predators. But there’s one problem: the cold.
Nighttime temperatures often dip below freezing in these rainy tropical highlands. How does a six-gram bird that needs nectar from 500 flowers a day just to survive get enough extra energy to keep itself warm all night?
Hummingbirds have scooped another record: they are not only tiny but can reach body temperatures below that of any non-hibernating mammal and any other bird.
The hummingbird is among a number of small creatures, including certain bats, that can enter a state known as daily torpor, a phenomenon where they turn down their metabolism and body temperature to save energy.
Metallura phoebe reaching a minimum Tb of 3.26°C, the lowest yet reported for any bird or non-hibernating mammal. The extent and duration of torpor varied among species, with overnight body mass (Mb) loss negatively correlated with both minimum Tb and bout duration. Findings suggest deep torpor is routine for high Andean hummingbirds, but evolved species differences affect its depth.
The team found that 24 of the 26 birds, covering all six species, entered torpor; however their lowest body temperature varied between individuals and between species.
The body temperature of one black metaltail hummingbird fell to just 3.3C which, they said, was not only a record for hummingbirds, and indeed all birds, but was lower than the record for non-hibernating mammals. The previous record for birds was 4.3C, reported for the common poor will, the only species of bird known to hibernate.
Source: Biology Letters