In fact, they found that birds using torpor only briefly could lose up to 15 percent of their body weight. Birds that took longer rest, in the order of 12 hours, lost only 2 percent. Birds that reach lower temperatures also lose a smaller percentage.
Some species, such as sparkling violetear, drop to a set temperature (in this case, approximately 46 degrees Fahrenheit) regardless of ambient temperature. Others, like black metal, seem to monitor the wind and are very cold. A metaltail hovered around 38 degrees Fahrenheit, marking the lowest recorded temperature of any hummingbird, to the researchers̵7; knowledge.
In fact, the metaltail, the black breast hill and the comet with a copper tail, associated with the species, are all cooler, longer lasting than the others. This will help explain why this group is more common at high altitudes – they have created ways to reduce the stress of living in an extreme environment.
These birds were held in captivity overnight, but Dr. McKechnie thinks that in a natural setting, hummingbirds can learn a lot about how to save energy.
There are stories of hummingbirds in the Andes entering a cave on cold spells and not appearing for days, a pattern that, if confirmed, would suggest that birds are capable of sleeping, he said. Like torpor, winter sleep saves an organism energy, but it lasts longer than a single night.
“For me, the next step beyond this study is to get a clear idea of where they are evolving,” Drs.