Biology prof climbs high to understand hummingbirds
By Leslie Linthicum
The air is thin up in the Peruvian Andes, but dozens of species of hummingbirds don’t seem to mind. They dart, hover and expend fantastic amounts of energy feeding their insatiable appetite for nectar at elevations of 13,000 feet and above.
Christopher Witt, an associate professor of biology at UNM, has chosen the mountains surrounding Lima for his extensive field study of the evolution of hummingbirds and their adaptation to high altitudes.
"We like to push the boundaries of altitude," says Witt, who scouts locations to gain the trust of local Peruvians, then packs in equipment on mules and sets up camp for weeks at a time.
His research in Peru, home to 125 different species of hummers, has yielded some scientific breakthroughs in the understanding of how the smallest birds on the planet take in and expel oxygen and how they adapt genetically to thinner air.
"We seek to understand why animals live where they live," says Witt. "The first question is how do they thrive in the mountains when they're living on the brink metabolically? And then the question is, with higher temperatures, will they be shifting up slope and how will they adapt to lower pressures than they're used to?"
Last year was a big one for Witt. He and his UNM team were featured in the PBS Nature documentary "Super Hummingbirds," where Witt—wearing loads of Lobo gear—showed off his high-mountain, high-tech field laboratory that allows him to fly hummingbirds under variable oxygen levels while he observes their behavior.
Witt and his team worked at about 13,000 feet elevation (roughly the height of Wheeler Peak, New Mexico's tallest mountain), where oxygen pressure is only about 40 percent of what it is at sea level. To test how well various hummingbird species are adapted to low-oxygen environments, Witt lowered the oxygen level even further inside his flight chamber to mimic higher and higher elevations.
Only when the oxygen level reached the equivalent of just under 42,979 feet, a staggering 14,000 feet higher than Mount Everest, was Witt's tiny test subject forced to stop hovering. Recovery was quick after the trial. The bird flew away unfazed.
A paper based on Witt's Andean bird research was published in Science last October. Witt and Jay Storz of the University of Nebraska studied hemoglobin proteins to see whether the evolution of molecules is predictable when species shift in elevation. They found that hemoglobin nearly always bound to oxygen more readily after bird lineages ascended the mountains, but that the DNA sequences underlying those changes were unpredictable. All of the research was based on frozen tissue samples from the ultra-cold archives at UNM's Museum of Southwestern Biology.
Commenting in The Scientist, Joel McGlothlin, who studies evolution at Virginia Tech, said Witt and Storz's work provides "a beautiful example of how we can make sense out of unpredictability by looking at deep evolutionary history."
Unpredictability is on Witt's mind. How climate change will affect the world's bird population is central to his research. Global warming will definitely have an effect on where birds live in the future, Witt says, but just how is hard to predict. Already hummingbird distribution has changed, with some species dramatically expanding their ranges. Other hummers are shifting their ranges to higher elevations and an important question, Witt says, is whether more dominant species will displace others.
Witt, curator of birds in the Museum of Southwest Biology on campus, proudly opens cabinet after cabinet and pulls out trays of stuffed birds—owls, cranes, parrots and of course dozens and dozens of brightly colored hummingbirds.
Some of Witt's earliest memories involve birds. Raised in urban Philadelphia, his bird watching was confined to what was on the streets—pigeons, starlings and house sparrows.
Though neither of his parents were birders, "I was always interested in birds," he says.
Two fortuitous events helped start him on his path to ornithology. The father of one of his friends in middle school was an avid bird watcher and took the boys on birding trips all over the Mid-Atlantic states. And Witt happened to live near the Academy of Natural Sciences, the oldest natural history museum in the Americas and one of the world's best.
He got a summer job there when he was 15 and became smitten by the world of birds.
"It's such an exciting diversity," says Witt, who came to UNM in 2007 after a post-doc at the University of California, Berkeley. "Form, function, color, sound—birds are absolutely spectacular!"
After an ecology degree from the College of the Atlantic, Witt got his Ph.D. at Louisiana State University, where he started focusing on hummingbirds and doing field research in the Andes.
At age 42, he has already confirmed that the hummingbird—the smallest bird—has the smallest and least variable genome among bird families and that different species of hummingbirds have similar evolutionary changes as they adapt to new elevation zones.
"The science is getting more exciting all the time," Witt says.
His personal life has seen a bit of an uptick in excitement since his starring role in "Super Hummingbirds," which was shown across the country on PBS stations. Although he is happily married with two kids, "I've got groupies!" Witt says, and he pulls out his cell phone to confirm the fact by showing a gushing email from a fellow bird-lover. "Of course," he says, "they're all over 70."