Scientists Took Hummingbirds Up a Mountain to See What Climate Change Would Do to Them

Scientists are trying to understand how many species might struggle with trying to find a new home as temperatures around the world shift dramatically.

Animals going to higher ground face two issues: colder temperatures and thinner, less oxygen-rich air. A group of Anna's hummingbirds were taken on a trip some 1,200 meters above their normal habitat.

As the hummingbirds hovered, their metabolism rates decreased. They flew shorter durations with less efficiency, most likely to get more oxygen.

The cooler elevation has a chilling effect on the hummingbird&s sleep patterns. The birds entered a kind of mini-hibernation more often when they were sleepy, which depressed their metabolism by 37 percent.

In the case of hummingbirds, going to higher ground would be a significant challenge according to the team behind the study.

The researchers wrote in their paper that lower oxygen availability and low air pressure may be difficult challenges to overcome for hummingbirds shifting upslope if there is little to no long-term acclimatization.

These birds are already having to move their homes because of rising temperatures, and can be found at altitudes of between 10-2,800 meters. The research team was interested to see if there was an upper limit to the distance and range of temperatures.

In this study, 26 hummingbirds were relocated from all over the elevation range, and they all struggled to adapt. The study found that those from higher altitudes had larger hearts for better circulation of oxygen around the body.

The researchers used a variety of methods to measure sleep levels and metabolic rate in the hummingbirds, including syrup-filled funnels to get the birds to eat while monitoring their oxygen consumption at the same time.

The production of carbon dioxide during sleep is an indicator of metabolism. The hummingbirds spent at least 85% of the night in a state of torpor or energy-saving mini-hibernation, compared with 70% normally. This was the same no matter what elevation the hummingbirds had been taken from.

It means that even if they are from a warm spot, they use torpor when it is cold.

The high-energy lifestyle of hummingbirds makes them great study subjects. They are able to cope with a variety of weather conditions, but unless they do it slowly enough for their bodies to adapt, they might not be able to move to higher ground.

The researchers think that the hummingbirds may eventually have to move further north because they can also change their latitude.

The authors of the study suggest that future studies and models should not look at temperature as a cause for species shifting location. Water and oxygen availability are other factors that need to be considered.

To fully understand a species' capacity to shift in response to a warming climate, it is critical to both assess its performance within its current range and compare this with performance beyond its current distribution.

The Journal of Experimental Biology published the research.