Scientists Took Hummingbirds Up A Mountain To See What Climate Change Would Do To Them

Scientists Took Hummingbirds Up A Mountain To See What Climate Change Would Do To Them

As temperatures around the world change dramatically, wildlife is often forced to move to find suitable habitats – and scientists are working hard to try to understand how many species may be struggling to find new homes.

Animals that travel to higher ground face two problems: colder temperatures and thinner, less oxygen-rich air (making it harder to breathe). In a new study, a group of Anna’s hummingbirds (calypte anna) were taken on a journey some 1,200 meters (4,000 ft) above their normal habitat.

Curiously, the hummingbirds’ metabolic rates actually decreased while hovering. They also flew shorter durations with less efficiency, probably from lack of oxygen.

While future temperatures could be warmer, for now, cooler altitudes have a crippling effect on hummingbird sleep patterns. When the birds slept, they went into a kind of mini-hibernation more often, which also reduced their metabolism by about 37% on average.

The team behind the study says that in the case of hummingbirds at least, getting to higher ground would pose a significant challenge.

“Our results suggest that low oxygen availability and low atmospheric pressure can be difficult challenges for hummingbirds to overcome as they move upward due to rising temperatures, especially if there is little or no long-term acclimation,” the researchers write in their published paper.

These birds are already having to relocate in response to rising temperatures and are currently found at elevations between 10 and 2,800 meters (33 to 9,186 feet). This covers a fairly large distance and temperature range, but the research team was interested to see if there was an upper limit.

For this study, 26 hummingbirds were moved from this entire current altitude range, and they all had more or less equal difficulty adapting. However, the study found that those at higher altitudes tended to have larger hearts for better oxygen flow through the body.

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

Carbon dioxide production during sleep was also recorded, another indicator of metabolic rate. Hummingbirds spent at least 87.5% of the night in an energy-efficient torpor or mini-hibernation state, compared to 70% normally. Again, this was consistent regardless of the altitude from which the hummingbirds were collected.

“That means that even if they come from a warm or cool place, they use torpor when it’s super cold, which is cool,” says ecologist Austin Spence from the University of Connecticut.

Hummingbirds make excellent study subjects in this case due to their high-energy lifestyle. They are able to cope with a variety of weather conditions, but it seems that moving to higher ground might be impossible for them – unless they do it slowly enough for their bodies to adapt.

However, the species don’t necessarily need to go to higher ground to find cooler temperatures, as they can also change latitudes – and the researchers believe these hummingbirds may eventually need to venture further north.

The study authors also suggest that future studies and models should not simply consider temperature as a trigger for species movement. Other factors, including the availability of water and oxygen, must also be considered.

“To fully understand a species’ ability to move in response to a warming climate, it is essential both to assess its physiological performance within its current range and to compare it with performance beyond its current distribution. “, write the researchers.

The research was published in the Journal of Experimental Biology.

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