At first, National Geographic Explorer Anusha Shankar had no interest in birds. “I thought they were too mainstream,” says Shankar, a doctoral candidate in Ecology and Evolution at Stony Brook University in New York. “Everyone studies them, they’re so easy to find. Who wants to do that?” She found reptiles and insects much more compelling. But in 2012, Shankar started her PhD with an advisor doing research on hummingbirds. Now she’s at the forefront of an effort to understand how hummingbirds balance their daily energy needs, and by extension, how other animals manage energy to survive a changing environment.
Hummingbirds have an enormous appetite; the human equivalent of their metabolism would require us to consume 300 hamburgers a day, Shankar says. What scientists don’t yet understand is what the birds specifically do with that energy. Shankar, who grew up in India, hopes her project will provide some insights into hummingbirds’ energy-budgeting strategies, opening a window into their adaptability.
For her field work, Shankar spent over a year in Ecuadorian Andes, home of 150 different species of hummingbirds, and several months in Arizona, which has one of the highest hummingbird densities in the United States. She and her research assistants would string fine mesh nets in front of clusters of flowering plants to capture test subjects. Then they banded each hummingbird, recorded metrics such as bill and claw length, and injected a harmless amount of stable double isotopes of water into the bird’s chest muscle. Shortly afterward she collected her main interest: a urine sample. (“I’ve become the hummingbird pee person,” she acknowledges.) Twenty-four hours later they would try to recapture the bird and collect another sample. From such data, Shankar can extrapolate energy usage over time, as well as how different environmental variables, such as temperature and altitude, affect that.
To understand how hummingbirds use energy at night, Shankar analyzed torpor, the hibernation-like state that the birds go into to conserve energy. She and her research assistants placed individual birds in respirometry chambers to measure the oxygen in their breath—and therefore how much energy they expend every second. They also used infrared cameras to show the pattern of a hummingbird’s skin temperature warming and dropping as it slept.
These experiments confirmed what scientists already knew from studying hummingbirds in a lab—that during torpor, hummingbirds can drop their energy consumption rate down to a mere two percent. But that’s a rare extreme. The average in the wild is about 16 percent. And what matters isn't how low they can go, but rather the total time a hummingbird spends in torpor. "A hummingbird that uses torpor for many hours but doesn’t save all that much energy per hour of torpor is better off than a hummingbird that maxes out its energy savings per hour during torpor but doesn’t stay there for very long,” she says.
The finding is just one example of why Shankar and her collaborators feel that there's a big benefit to taking this type of work out into the field, instead of restricting it to a laboratory or aviary. "Imagine if I was studying human energy use and I put a Fitbit tracker on you and put you in a box,” Shankar says. "I'd get a very different answer than if you wore the Fitbit while going about your regular life.”
Because hummingbirds expend energy quickly but have barely any fat to store it, their survival directly depends on a high-calorie food source: the nectar of flowers like bee balm and Coral honeysuckle. Although hummingbird distribution can’t be mapped via remote sensing, we do know the distribution of the plants they rely on. So Shankar’s plan is to marry plant-distribution maps with climate data, adding in the detailed knowledge of hummingbird biology and physiology that she’s been acquiring in the field, to model the effects of climate change on the behavior of hummingbirds and other animals. Ultimately, she wants to know if their energy budgets could become so tight that they can’t survive.
Amid her research, Shankar carves out time to co-produce two websites that aim to make science more understandable and engaging to the layperson. Brainchem-ecology.com presents scientific concepts as infographics (her favorite explains why you must refrigerate eggs in the U.S. but not in India). And ScienceOutside.com collects narrative tales about mishaps in the field, showing “the human side of science,” as Shankar says. “Because scientists step in cow poop, too.”
Her doctorate work with hummingbirds is an extension of Shankar's belief that science is for everyone. “PhDs are notorious for being super concentrated in this tiny, obscure part of something,” she says. “I think what’s more relevant to most people is broader-scale patterns, not only what’s going to happen to birds, but what’s going to happen to all of us.”