Hummingbirds could be wiped out by global warming, scientists say
Hummingbirds could be wiped out by global warming, a new study warns. They will have to move north to seek cooler climates – or disappear, scientists say.
Hummingbirds perform the most exhausting type of flight in the animal world. Their soaring habit requires much more energy and oxygen than conventional flight.
However, the rarefied air does not constitute any barrier for these birds. They thrive on top of high mountain ranges from Alaska to South America.
A study found that the challenges of relocation may be too much for small, nimble aeronauts.
Lead Author Austin Spence, Ph.D. student at the University of Connecticut, said: “Taken together, these results suggest that low atmospheric pressure and oxygen availability may reduce the hovering performance of hummingbirds when exposed to the acute challenge of high altitude conditions.”
The thinner, colder air is especially problematic for creatures that struggle to warm up when less oxygen is available.
The study involved Anna’s hummingbirds (calypte anna) which are comfortable up to altitudes of around 2,800 meters (9,000 ft).
They lured them into net traps from sites in California – ranging from 10 meters (30 feet) above sea level in Sacramento and up to 2,400 meters (7,800 feet) in Mammoth Lakes.
Then the researchers transported them to a western California aviary at 1,215 meters (3,900 feet).
Once the birds had spent a few days in their new home, a tiny funnel was set up that they could insert their heads into while hovering while sipping on a tasty syrup.
Metabolic rate was measured overnight as the tiny creatures let their metabolism drop when they rested.
The mini-hibernation form conserves energy during sleep. Hummingbirds can cool their bodies to less than 4°C (39.2°F) at night – the lowest temperature recorded in a bird.
They have wings that beat more than 10 times per second and during the day they use their hovering ability to suck nectar from thousands of flowers.
To keep up, their little hearts beat around 1,000 times per minute, but this drops to just 50 during rest.
Spence and his colleagues moved the birds to a nearby research station at 3,800 meters (12,000 feet) near the summit of Mount Barcroft.
The air is thinner with about 39% less oxygen and about 5°C (41°F) colder. After four days at the new altitude, metabolic rates were again assessed.
The hovering hummingbirds should have worked harder to stay aloft 1,000 meters (3,200 feet) above their natural range, but they actually suffered a 37% drop in their metabolic rate. When the team compared the energy used by birds native to sea level and the upper end of their range, they all struggled similarly at the top of the mountain.
Additionally, the birds resorted to lowering their metabolic rate for longer periods at night. They spent more than 87.5% of the cold night at high altitude in torpor.
Spence said, “That means even if they come from somewhere hot or cool, they use torpor when it’s super cold, which is cool.”
The team also checked the size of the animals’ lungs to find out if they grew larger in those that came from higher altitudes to compensate for the low oxygen supply.
They do not have.
But birds had bigger hearts to circulate oxygen through the body.
The discoveries in the Journal of Experimental Biology have implications for the future of hummingbirds as they seek more comfortable conditions due to climate change.
Spence added: “‘Our results suggest that low oxygen availability and low atmospheric pressure may be difficult challenges for hummingbirds to overcome.”
This story was provided to Newsweek by Zenger News.