Wednesday, August 17, 2022

High altitude may be a climatic haven for some birds, but not for these hummingbirds

Cooler, higher locations may not be very welcome for some hummingbirds trying to escape rising temperatures and other effects of climate change.

Anna’s hummingbirds live no higher than about 2,600 meters above sea level. If birds try to expand their range to include higher altitudes, they may struggle to fly well in thin air, researchers report May 26 Journal of Experimental Biology,

These sparrows have expanded their range in the past. Once found only in Southern California, the birds now live north of Vancouver, says Austin Spence, an ecologist at the University of California, Davis. That expansion is probably due to climate change and people using feeders to attract hummingbirds, he says.

Spence and his colleagues collected 26 of Anna’s sparrows (Calypte Anna) from different altitudes in the natural range of birds in California. The team transported the birds to an aviary about 1,200 meters above sea level and measured their metabolic rate while they were hovering. After relocating the hummingbirds to a field station at 3,800 meters altitude, the researchers let the birds rest for at least 12 hours and then measured that rate again.

At higher altitudes than at the aviary, there was an average 37 percent lower rate, even though the birds must have worked harder to stay aloft in thin air (SN: 2/8/18) At higher altitudes, hovering, which takes a lot more energy than other forms of flight, is more challenging and requires even more energy, Spence says. He says the reduction in metabolic rate suggested that the birds’ hovering performance was deteriorating. “Low oxygen and low air pressure can hold them back as they try to move upward.”

Additional work is needed to see if birds may be able to adjust better if they are given weeks or months to gradually adapt to conditions at higher altitudes.

Nation World News Desk
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