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Hummingbirds have evolved to survive harsh environments 

Experts at Washington University in St. Louis are describing how hummingbirds use torpor, a hibernation-like state of inactivity, to survive harsh environments. According to the study, hummingbirds use torpor in different ways depending on their physical state and the environmental conditions they are facing. 

In collaboration with biologists in Colombia, the researchers caught 249 hummingbirds (29 different species) living in the middle to high altitudes of the Andes Mountains. The experts wanted to measure torpor under various semi-natural conditions. 

“Torpor is somewhere between a power nap and hibernation,” said study first author Justin Baldwin. “Earlier research had suggested that torpor was a way of completely shutting metabolism down to minimal levels.”

“Our findings join a growing body of evidence to suggest that when animals enter torpor, they have diverse options to calibrate aspects of torpor to their environment.”

The study revealed that hummingbirds can enter into deep or shallow torpor, and they can remain in this state for just a few hours or for the entire night. In addition, the birds can begin to emerge from torpor hours or just minutes before sunrise. 

“Small birds were more likely to use torpor than large birds, but only at low ambient temperatures, where torpor was prolonged. We also found effects of proxy variables for body condition and energy expenditure on the use of torpor, its characteristics, and impacts,” wrote the researchers.

Study co-author Gustavo Londoño is a professor at the Universidad Icesi in Cali, Colombia. He explained that torpor can be the difference between surviving through cold night-time temperatures encountered at high elevations, or dying trying to regulate their body temperature using fuel from their internal reserves.

“One of the new things we learned with this study is that hummingbirds start exiting torpor more or less one hour before sunrise,” said Professor Londoño. “Being out of torpor and ready to fly with the first sunlight is key to ensuring that their first meal will be from flowers that are full of nectar. The flowers then get depleted through the morning.”

By studying many hummingbird species at once, the researchers were able to analyze how torpor may have contributed to their evolution and colonization of harsh environments.

“Species that more readily deployed torpor at our study sites also occurred at higher elevations across the entire Andean region,” said Baldwin. “This is exciting, because it suggests that a characteristic of bird physiology can tell us something about their distribution across the entire continent.”

“Even though we don’t know which came first – an increase in readiness to use torpor or the ability to persist at high elevations – we think that hummingbirds’ readiness to use torpor is likely tied to their evolutionary conquest of mountain habitats.”

 The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

By Chrissy Sexton, Editor

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