With temperatures around the world changing so dramatically, wildlife is often forced to relocate to find suitable habitat – and scientists are working hard to try to understand how many species may struggle as they try to find a new home.
Animals that go to higher ground face two problems: cooler temperatures and thinner, less oxygen-rich air (so it’s harder to breathe). In a new study, a group of Anna’s hummingbirds (Caleb Anna) in flight at an altitude of 1,200 meters (4,000 feet) above their natural environment.
Oddly enough, hummingbirds’ metabolic rates actually decreased while they were in flight. They also fly for shorter periods with less efficiency, most likely due to lack of oxygen.
While temperatures in the future may be warmer, cooler altitudes have a chilling effect on a hummingbird’s sleep patterns. When the birds slept, they went into a kind of mini-hibernation more often, which also reduced their metabolism by an average of 37 percent.
The team behind the study says that in the case of hummingbirds at least, going to higher ground will be a major challenge.
In their report, the researchers wrote: “Our results suggest that low oxygen availability and low air pressure may be difficult challenges to overcome for hummingbirds that move from top to bottom as a result of rising temperatures, especially if there is little long-term acclimatization.” published paper.
These birds are already forced to move their homes in response to rising temperatures, and they can currently be found at altitudes between 10 and 2,800 meters (33-9186 feet). This covers a distance and range of temperatures, but the research team was interested to see if there was an upper limit.
In this study, 26 hummingbirds were flown from across the current altitude range, and they all struggled equally to adapt. However, the study found that those from higher elevations tended to have larger hearts to improve oxygen distribution around the body.
The researchers used a variety of methods to measure sleep levels and metabolic rate in hummingbirds, including a funnel filled with syrup to get the birds to eat while simultaneously monitoring their oxygen consumption.
The production of carbon dioxide during sleep, which is another indicator of the metabolic rate, has also been recorded. Hummingbirds spent at least 87.5 percent of the night in small, energy-efficient hibernation, compared to 70 percent typically. Again, this was consistent no matter what altitude the hummingbirds were taken from.
“This means that even if they’re from a warm or cold place, they use hibernation when it’s very cold, and it’s cold,” Ecologist Austin Spence says: from the University of Connecticut.
Hummingbirds make great study subjects in this case because of their high-energy lifestyle. They are able to handle a wide variety of weather conditions, but it seems that moving to higher ground may be far from them – unless they do it slowly enough for their bodies to adapt.
However, species don’t necessarily have to go to higher altitudes to find cooler temperatures, because they can change their latitude, too—and the researchers think these hummingbirds may eventually have to venture north.
The study authors also suggest that future studies and models should not simply view temperature as a trigger for changing the location of species. Other factors, including the availability of water and oxygen, must also be considered.
“To fully understand a species’ ability to shift in response to global warming, it is necessary to assess its physiological performance within its current range and compare it to performance beyond its current distribution,” write researchers.
The search was published in Journal of Experimental Biology.
