Hummingbirds will not be able to retreat to high altitudes

Many plant and animal species are seeking refuge in higher elevations to escape the stress of rising temperatures.  In a study funded by the National Science Foundation, experts have discovered that hummingbirds will not be able to adjust to life at higher altitudes, and this is primarily due to lower oxygen availability.

“Many species have not tracked their thermal niches upslope as predicted by climate change, potentially because higher elevations are associated with abiotic challenges beyond temperature. To better predict whether organisms can continue to move upslope with rising temperatures, we need to understand their physiological performance when subjected to novel high-elevation conditions,” wrote the study authors. 

“Here, we captured Anna’s hummingbirds – a species expanding their elevational distribution in concordance with rising temperatures – from across their current elevational distribution and tested their physiological response to novel abiotic conditions.”

After the birds had time to adjust to a high-altitude habitat, the researchers measured their metabolic rates. The results showed found that these rates had dropped by nearly 40 percent compared to the rates measured in the birds’ natural habitat.

“Overall, these results suggest low air pressure and oxygen availability may reduce hovering performance in hummingbirds when exposed to the challenge of high-elevation conditions,” said study lead author Austin Spence of the University of Connecticut.

According to the experts, the birds also spent more time in a torpid state at higher altitudes regardless of the elevation of their original habitat. “Whether they’re from a warm or cool spot, they use torpor when its super-cold,” said Spence.

Hummingbirds from higher elevations do not have enlarged lungs to compensate for a lack of oxygen, but their hearts are larger and can circulate more oxygen.

“Our results suggest lower oxygen availability and low air pressure may be difficult challenges to overcome for hummingbirds,” said Spence. 

“Future studies should investigate how chronic exposure and acclimatization to novel conditions, as opposed to acute experiments, may result in alternative outcomes that help organisms better respond to abiotic challenges associated with climate-induced range shifts,” concluded the researchers.

The study is published in the Journal of Experimental Biology.

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By Chrissy Sexton, Earth.com Editor