Between November and May, Anna’s hummingbirds, a common hummingbird species on the US West Coast, come to the California lowlands to play before migrating to higher elevations in the summer. These tiny red and green creatures span the entire west coast from Baja California to British Columbia.
But as the Earth warms and global temperatures continue to rise, it’s possible these fast-paced birds will find it harder to flee to higher altitudes, new research shows. The results were released on Thursday Journal of Experimental Biology.
Here is the background – Scientists have observed how animals and plants are adapting to global warming by migrating to the poles and higher elevations, seeking cooler temperatures when their natural habitats get too hot. Austin Spencethe study’s lead author, a conservation biologist and postdoctoral researcher at the University of California, Davis, likens this adaptation to using air conditioning in hot weather.
“Think of air conditioning. If I’m too hot, I can turn it down. If an animal or a plant is too hot, they can’t turn down the air conditioning,” says Spence Vice versa. But they can relocate to areas that have the weather they’re used to, he says.
But species are not always moving in the direction we would expect as a result of the climate crisis. Factors other than temperature variations – such as oxygen availability and barometric pressure – could affect whether animals are physiologically able to move to higher altitudes.
Due to human encroachment on their habitats, Anna’s hummingbirds have already migrated north from southern California to Canada. Therefore, these birds can help scientists understand how animals may migrate to higher elevations in response to a changing environment.
“Anna’s hummingbirds are a great study system because they’ve already had their life history altered by humans,” says Spence.
What’s new – However, Spence’s research suggests that the colorful hummingbird’s ability to adapt to higher elevations outside of its usual habitat range may be limited.
First the good news: hummingbirds respond to colder temperatures at higher altitudes by becoming more torpor. Torpor is a condition that allows hummingbirds to conserve energy in colder temperatures by slowing metabolic functions, including lowering their heart rate. Anna’s hummingbirds, already living at higher altitudes, have been found to possess larger hearts than hummingbirds from lower elevations, suggesting that the bodies of these birds may have adapted to higher-altitude, less oxygenated environments.
Now for the potentially bad news: Anna’s hummingbirds exhibited a lower hovering metabolic rate at altitudes above their normal altitude range – a measure of how much energy the hummingbird expends while hovering. In other words, reduced oxygen and lower air pressure at higher altitudes reduced the hummingbird’s energy efficiency and hampered its ability to fly effectively.
“Due to the lower oxygen levels, it can be difficult for hummingbirds to move to higher elevations,” says Spence.
What it means – Birds need to fly to pollinate plants, find food, mate, and generally survive. If hummingbirds can’t fly as efficiently in lower oxygen conditions at higher altitudes, then that’s a problem.
“In our study, individuals could not fly as effectively or for as long when they were above their altitude range limit,” the researchers write.
According to Spence, animals find it difficult to thrive at higher elevations for two reasons: cold temperatures and hypoxic — low-oxygen — conditions. The hummingbirds have been able to adapt to the colder temperatures, which still leaves the oxygen problem. While climate change won’t affect oxygen levels any further, Spence says the already low levels at higher elevations could “slow down” the hummingbirds’ ability to migrate to higher altitudes.
“Our results suggest that Anna’s hummingbirds exhibit an acute response to novel hypoxic states that are certain to persist as temperatures rise,” the researchers conclude.
How they did it – To study how Anna’s hummingbirds fare at altitudes above their usual altitude range, the scientists first took a small sample of the birds and observed them at a location within their normal altitude range at about 1215 meters (3986 feet) above sea level in the Sierra Nevada and White Mountain Ranges in California.
The scientists then took the birds to a location about 3,800 meters (12,467 feet) above sea level, well beyond the upper limit of the hummingbird’s altitude range. Comparing how birds flew at the normal altitude range versus the higher altitudes allowed the researchers to draw conclusions as to whether Anna’s hummingbirds might be able to move and survive higher up in the mountains.
What’s next – It’s not all doom and gloom for the colorful hummingbird.
Yes, hummingbirds initially struggled to cope with lower oxygen levels at higher elevations, but it’s possible that over an extended period of research the birds acclimatize — adapt — to their new environment. The researchers call for further studies to examine “whether individuals have the ability to acclimate, or whether evolution is necessary to successfully colonize new habitats.”
We already know that Anna’s hummingbirds can thrive alongside humans in cities, and since they naturally move seasonally to higher elevations, Spence says we can observe hummingbirds that resemble “a canary in a coal mine” to see how the animals are faring , if they continue to move uphill.
“Fortunately, Anna’s hummingbirds thrive in human environments,” concludes Spence.
So the future might be bright for this tiny little pollinator floating around in your flower bed.
https://www.inverse.com/science/climate-change-spells-bad-news-for-hummingbirds Can hummingbirds survive climate change? Scientists say it’s complicated