Black Metaltail, the coolest of birds | Metallura phoebe

[Posted by Chuck Almdale]

It’s hard enough to believe that tiny hummingbirds can thrive in the high Andes, but many do very well in the very thin air and painfully cold nights. There can be a lot of flowers up there that no other birds are using, so competition for sugar is reduced. And they get through the night by going into torpor, a temporary hibernation-like state where they slow everything way down.

• Body temperature drops from 40°C (104°F) to 3.26°C (37.9°F), as low as 1°C above ambient air temperature
• Heart rate drops from 1,200 beats/minute to as low as 40 beats/minute
• Torpor cuts their energy use by 95%
• This is the lowest temperature ever recorded in birds or non-hibernating mammal
• Torpor investigations done at over 12,460 ft. in the Andes
  

Video of Black Metaltail in flight – 50 seconds

Link to original paper:
Extreme and variable torpor among high-elevation Andean hummingbird species
Royal Society Publishing | Blair O. Wolf, et.al. | 9 Sep 2020

Abstract:
Torpor is thought to be particularly important for small endotherms occupying cold environments and with limited fat reserves to fuel metabolism, yet among birds deep torpor is both rare and variable in extent. We investigated torpor in hummingbirds at approximately 3800 m.a.s.l. in the tropical Andes by monitoring body temperature (T_b) in 26 individuals of six species held captive overnight and experiencing natural air temperature (T_a) patterns. All species used pronounced torpor, with one Metallura phoebe reaching a minimum T_b 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 (M_b) loss negatively correlated with both minimum T_b and bout duration. We found a significant phylogenetic signal for minimum T_b and overnight M_b loss, consistent with evolutionarily conserved thermoregulatory traits. Our findings suggest deep torpor is routine for high Andean hummingbirds, but evolved species differences affect its depth.

This hummingbird survives cold nights by nearly freezing itself solid
The black metaltail goes into a state of suspended animation, becoming ‘cold as a rock’
Science News | Jonathan Lambert | 8 Sep 2020 | 2 min read

The Coolest Hummingbird, as Measured by an Actual Thermometer
Black Metaltail. The name seems fit for a hard-hitting rock band, but this bird’s cool factor goes way beyond its heavy-metal moniker.
Cornell Lab-All About Birds | Marc Devokaitis | 20 Dec 2020 |