Surviving at high altitudes is difficult for most living things because the air is less dense the higher you go. One consequence of this lower air density is less oxygen overall. Most human travelers to the top of Mount Everest (8,848 meters above sea level) will take advantage of portable oxygen, but some people manage the climb without any assistance.
Creatures with wings have an added problem when dealing with high altitudes: The lower air density makes flight a lot harder. Every flap of the wing results in less lift than it would close to sea level.
But there are many organisms that can fly to higher altitudes than had been thought possible. Finding them usually requires a bit more work than just looking up, though. Here are a few of the world’s highest fliers:
Most bar-headed geese (Anser indicus) migrate between their breeding areas in Mongolia, China or the Tibetan Plateau and wintering areas in India. This requires a flight through the Himalayas. A study, published in 2012 in the Proceedings of the Royal Society B, fitted 91 geese with GPS satellite trackers and found that the birds reached maximum flight altitudes of 7,290 meters when headed south and 6,540 meters on the northbound journey. The geese didn’t just fly up and over the world’s tallest mountain range, however. They tended to stick to the lower parts of the mountains, wending their way around the monoliths.
Researchers have been outfitting airplanes with insect-collection plates since 1926. Charles Lindbergh even had such devices on his famous 1933 flight across the Atlantic. But the highest insect caught with this method is a bit of a surprise, as we most often see it burrowing into our homes near the ground — the termite. A 1961 study (pdf) in Pacific Insects reported collecting the termite at an altitude of 5,790 meters over the Pacific.
Given their name, bumblebees don’t have a reputation for expert flying capabilities. But scientists have found these bees (genus Bombus) foraging on wildflowers on Mount Everest at altitudes of more than 5,600 meters. To test how the bees manage to fly in such thin air, Michael Dillion and Robert Dudley of the University of California, Berkeley simulated high elevations by reducing the air density in a chamber in the lab. In a study published February 5 in Biology Letters, they report that their test insects could fly at an altitude as high as 7,500 meters. A couple of bees could even handle altitudes of 9,000 meters — higher than Everest. The insects managed this feat not by beating their wings more frequently, but by increasing the angle of their wing beats.
The tiniest fliers don’t even need wings. Scientists collected cells on research flights that took place in several locations across the United States, Caribbean, Gulf of Mexico and Atlantic Ocean in 2010 as part of a program to measure air masses associated with tropical storms. They then used gene sequencing to figure out exactly what they collected. There were plenty of bacteria at altitudes as high as 8,000 to 10,000 meters, including some from the familiar (and somewhat worrisome) genuses — Escherichia and Streptococcus — collected during flights over populated areas after hurricanes. The microbes might play a role in the formation of clouds and precipitation, researchers reported in the Proceedings of the National Academy of Sciences last February.