Silence Of The Hums – Hummingbirds “Could Be Wiped Out By Global Warming” – The Florida Star
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, a PhD student at the University of Connecticut, said: “Overall, these results suggest that low atmospheric pressure and low oxygen availability may reduce the hovering performance of hummingbirds when they are 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 focused on Anna’s hummingbirds (Calypte anna) which are comfortable up to altitudes of around 2,800 meters (9,000 feet).
They lured them into net traps from sites in California – ranging from 10 m (30 ft) above sea level in Sacramento and up to 2,400 m (7,800 ft) in Mammoth Lakes.
Then the researchers transported them to a western California aviary at 1,215 m (3,900 ft).
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 (40°F) at night – the lowest temperature recorded in a bird.
They have wings that beat more than ten 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 m (12,000 ft) near the summit of Mount Barcroft.
The air is thinner with about 39% less oxygen and about 5°C colder. After four days at the new altitude, metabolic rates were again assessed.
Hovering hummingbirds would have had to work harder to stay aloft 1,000 m (3,200 ft) above their natural range.
But they actually experienced 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.
Findings from the Journal of Experimental Biology have implications for their future as they seek more comfortable conditions due to climate change.
Spence added, “Our results suggest that low oxygen availability and low atmospheric pressure can be difficult challenges for hummingbirds to overcome.”