(ORDO NEWS) — With drastic temperature changes around the world, wild animals are often forced to move to find suitable habitat, and scientists are working hard to understand how many species may find it difficult to find a new home.
Animals moving to higher elevations face two challenges: colder temperatures and thinner, less oxygenated air (so it’s harder for them to breathe).
In a new study, a group of Anna’s hummingbirds (Calypte anna) were sent on a journey up to about 1,200 meters (4,000 feet) above their usual habitat.
Curiously, the metabolic rate of hummingbirds decreased as they soared. They also made shorter flights with less efficiency, most likely due to lack of oxygen.
While temperatures may be warmer in the future, for now, cooler altitudes have a cooling effect on hummingbird sleep patterns.
When the birds napped, they were more likely to go into a sort of mini-hibernation, which also lowered their metabolism by an average of about 37 percent.
The team behind the study says that, at least for hummingbirds, moving to higher ground is a major challenge.
“Our results suggest that low oxygen availability and low barometric pressure can be challenging problems for hummingbirds moving upslope as a result of rising temperatures, especially if there is little to no long-term acclimatization,” the researchers wrote in the published paper.
These birds are already forced to move their homes due to rising temperatures and can currently be found at altitudes ranging from 10 to 2800 meters (that’s 33 to 9,186 feet). This is a fairly large distance and temperature range, but the research team was interested to know if there was an upper limit.
For this study, 26 hummingbirds were relocated from every corner of the current altitude range, and they all tried more or less equally to adapt. However, the study found that birds from higher altitudes tend to have larger hearts for better oxygen circulation throughout the body.
To measure sleep levels and metabolic rates of hummingbirds, the researchers used a variety of methods, including syrup-filled funnels to force the birds to eat while monitoring their oxygen intake.
The release of carbon dioxide during sleep was also recorded – another indicator of metabolic rate. Hummingbirds spent at least 87.5 percent of their nights in a state of torpor or energy-saving mini-hibernation, up from 70 percent under normal conditions. And again, this happened regardless of the height from which the hummingbirds were taken.
“This means that even if they are from a warm or cool place, they use torpor when it gets very cold,” says ecologist Austin Spence of the University of Connecticut.
In this case, hummingbirds make excellent subjects of study due to their high-energy lifestyle. They are able to cope with various weather conditions, but it seems that moving to higher ground may not be possible for them – unless they do it slowly enough for their bodies to adapt.
However, in order to find cooler temperatures, species don’t have to move to higher ground, as they can also change their latitude – and the researchers believe these hummingbirds will eventually have to travel further north.
The authors of the study also believe that future studies and models should not consider temperature only as a trigger for species relocation. Other factors need to be taken into account, including the availability of water and oxygen.
“To fully understand a species’ ability to move in response to a warming climate, it is critical to assess its physiological performance within its current range and compare it to that outside its current range,” the researchers wrote.
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