Between November and May, Anna’s hummingbird, a common hummingbird species on the US west coast, comes out to play in lowland California before migrating to higher ground during the summer. These tiny red and green creatures are scattered all over the West Coast from Baja California to British Columbia.
But as the Earth warms and global temperatures continue to rise, it’s possible that these whizzing birds will have a harder time escaping to higher altitudes, new research suggests. The findings were published Thursday in Journal of Experimental Biology.
Here’s the background- Scientists have observed animals and plants adapting to global warming by migrating to the poles and higher altitudes, seeking cooler temperatures as their natural habitats grow too hot. Austin SpenceThe study’s lead author and a conservation biologist and postdoctoral researcher at the University of California, Davis, likened this adaptation to using air conditioning in hotter weather.
“Think of air conditioning. If I get too hot, I can turn it down. If animals or plants get too hot, they can’t turn off the air conditioner,” says Spence Backwards. But they can move to areas where the weather is normal, he said.
But species are not always moving in the direction we expect as a result of the climate crisis. Factors other than changes in temperature — such as oxygen availability and air pressure — can affect whether an animal can physiologically move to higher ground.
Due to humans disturbing their habitat, Anna’s hummingbird has moved north from Southern California all the way to Canada. Therefore, these birds could help scientists understand how animals might migrate to higher ground in response to a changing environment.
“Anna’s hummingbirds are a great system of study because they have changed their life history because of humans,” Spence said.
What’s new – But Spence’s research suggests there may be limitations to the colorful hummingbird’s ability to adapt to higher altitudes outside its usual habitat range.
First, for the good news: Hummingbirds respond to cooler temperatures at higher altitudes by increasing torpor. suspended animation is a condition that allows hummingbirds to conserve energy in colder temperatures by slowing down metabolic functions, including lowering their heart rate. Anna’s hummingbirds already living at higher altitudes were found to have larger hearts than hummingbirds from lower altitudes, implying that these birds’ bodies may have adapted to the low-oxygen environment at higher altitudes.
Now, for the potentially bad news: Anna’s hummingbirds exhibit a lower hovering metabolic rate – a measure of how much energy a hummingbird uses while hovering – at altitudes above its normal altitude range. In other words: The reduced oxygen and lower air pressure at higher altitudes reduces the hummingbird’s energy efficiency, affecting its ability to fly effectively.
“It may be difficult for hummingbirds to move to higher ground because of the lower oxygen,” Spence said.
What does it mean – Birds need to fly to pollinate plants, find food, mate, and generally survive. If hummingbirds can’t fly as efficiently in low oxygen conditions at higher altitudes, then that’s a problem.
“In our study, individuals were not able to fly as effectively or as long as they were above their altitude range limit,” the researchers wrote.
Spence said the higher altitudes were difficult for animals to thrive for for two reasons: cold temperatures and hypoxic conditions – low oxygen. Hummingbirds are able to adapt to colder temperatures, which still leaves oxygen problems. While climate change won’t affect oxygen levels further, already low levels at higher altitudes could “slow” hummingbirds’ ability to migrate to higher ground, according to Spence.
“Our findings suggest that Anna’s hummingbird exhibits an acute response to novel hypoxic conditions, which will inevitably persist in the face of rising temperatures,” conclude the researchers.
How did they do it— To study how Anna’s hummingbirds fly at altitudes above their usual altitude range, scientists first capture small samples of the birds and observe them at locations within their normal altitude range of about 1215 meters (3986 ft) above sea level in the Sierra Nevada and Mountains. White stretches across California.
Then, scientists moved the birds to a location about 3,800 meters (12,467 ft) above sea level, well beyond the upper limit of the hummingbird’s altitude range. Comparing how birds fly within the normal altitude range versus higher altitudes allows researchers to draw conclusions about whether Anna’s hummingbird might be able to move and survive higher in the mountains.
What’s next – Not all doom and gloom for hummingbirds is brightly colored.
Yes, hummingbirds initially have a difficult time dealing with lower oxygen levels at higher altitudes, but it is possible that birds will adjust – adapt – to their new environment over a longer period of study. The researchers called for further studies to explore “whether individuals have the ability to adapt or whether evolution is required to successfully colonize a new habitat.”
We already know that Anna’s hummingbirds can breed in cities alongside humans, and because they naturally move to higher altitudes seasonally, Spence says that we can observe hummingbirds similar to “canaries in a coal mine” to see how animals move as they move further up.
“Fortunately, Anna’s hummingbird does very well in the human environment,” concludes Spence.
So the future may still be bright for the tiny pollinators hovering in your flowerbed.