July 14, 2022 - Climate change is making it more challenging for small animals like hummingbirds to reach heights that allow them to evade the impacts of a warming world. A team of researchers set out to study how Anna's hummingbirds (Calypte anna) would adjust to a higher altitude than that of their natural habitat. The scientists published their findings in the Journal of Experimental Biology.

The biologists, supported in part by the U.S. National Science Foundation, relocated the birds to two areas at much higher altitudes than their natural habitat. After an adjustment period, the team measured the hummers’ metabolic rates and discovered that they experienced a drop in metabolic rates approaching 40%.

"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 Austin Spence, one of the authors of the paper.

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.

While hummingbirds from higher elevations don't have enlarged lungs to compensate for the dearth of oxygen, their hearts are larger and can circulate more oxygen than their lower altitude counterparts.

"Our results suggest lower oxygen availability and low air pressure may be difficult challenges to overcome for hummingbirds," said Spence. Relocating to a higher altitude seems unlikely due to the drop in metabolic rate and increase in time spent in a torpid state.
Source: NSF