Hummingbirds may struggle to go any further uphill

Any animal ascending a mountain experiences a double whammy of impediments: The air gets thinner as it also becomes colder, which is particularly problematic for creatures struggling to keep warm when less oxygen is available. For tiny animals with the highest-octane lifestyles, such as hovering hummingbirds, the challenges of relocating to higher levels to evade climate change may be too much, but no one knew whether these extraordinary aviators may have more gas in the tank to keep them aloft at higher altitudes.