As temperatures around the world change dramatically, wildlife is often forced to relocate to find suitable habitats, and scientists are working hard to find out how many species might struggle as they try to find a new home.
Animals traveling to higher altitudes face two problems: lower temperatures and difficulty breathing due to thinner, oxygen-rich air.
To find out the extent of this problem, researchers released a group of Anna hummingbirds (Calypte anna) into an area about 1,200 meters above their normal habitat. Interestingly, hummingbirds’ metabolic rates decreased as they hovered. They also flew with less efficiency and for shorter durations, possibly because they needed more oxygen.
Future temperatures may be higher, but for now the cooler altitudes are having a chilling effect on hummingbird sleep patterns. When the birds slept, they more frequently entered some form of mini-hibernation, which lowered their metabolisms by an average of 37 percent.
The team behind the study think they have uncovered that moving to higher ground will pose a significant challenge, at least in the case of hummingbirds. In the paper published in
, the researchers write, “Our results suggest that lower oxygen availability and lower air pressure present difficult challenges for hummingbirds that fly to high altitudes as a result of rising temperatures, particularly if there is little or no extended acclimation period. It shows that it can happen.”
These birds already have to move their homes in response to rising temperatures and can now be found at altitudes between 10 and 2,800 metres. This covers a fairly wide temperature range, but the research team was trying to find out if there was an upper limit.
For this study, 26 hummingbirds were moved from all over the available altitude range, and all struggled to adapt by approximately the same amount. But this study found that those from higher altitudes tended to have larger hearts to allow oxygen to circulate better throughout the body.
Researchers used a variety of methods to measure hummingbirds’ sleep levels and metabolic rate, including syrup-filled funnels to get the birds to eat while monitoring their oxygen consumption.
Another indicator of metabolic rate, carbon dioxide production during sleep was also recorded. Hummingbirds spent at least 87.5 percent of the night in a state of drowsiness or energy-saving mini-hibernation, compared to 70 percent normally. Again, there was consistency here, regardless of what height the hummingbirds came from.
“This means that they use torpor when it’s super cold, even if they come from somewhere hot or cold,” says University of Connecticut ecologist Austin Spence.
The study authors also say that future studies and models should not look at temperature as a trigger for species relocation. The research is published in the Journal of Experimental Biology…
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