When hummingbirds go into slumber

As part of their ‘Sawaal-Jawaab’ sessions, the Tata Institute of Fundamental Research (TIFR) organised an interaction with Anusha Shankar at Aaromale Cafe recently. An Assistant Professor at the institute, she talked about how hummingbirds can ‘budget’ their daily activities to save energy
A composite thermal image of a hummingbird asleep at a high body temperature (left) transitioning to torpor by getting cold (right)
A composite thermal image of a hummingbird asleep at a high body temperature (left) transitioning to torpor by getting cold (right)| Anusha Shankar

HYDERABAD : Hummingbirds—small and light, with high metabolism— but with barely any backup energy in the form of fat. To save energy, they have a unique ability to go into a hibernation-like state called torpor at night. They get cold (50°F/10°C) sometimes every night, and rewarm safely every morning, without damaging organs like their hearts and brains,” said Anusha Shankar, a researcher at TIFR Hyderabad.

Explaining the behaviours of hummingbirds in an intriguing question-answer session at Aaromalé Café recently, she talked about the daily activity and energy manipulations of hummingbirds. Her passion lies in precisely this domain: understanding how animals meet their energy needs in different environments. For over a decade, she has delved into the world of hummingbirds. During her Bachelor’s and Master’s degrees, she studied king cobras, hoolock gibbons, and hornbills in India. She then went on to pursue a PhD at Stony Brook University, followed by two postdoctoral research stints at Cornell University and the University of Alaska Fairbanks.

Now, at TIFRH, she is studying wild Indian animals and their responses to human-dominated tropical environments. A National Geographic Explorer and a Ramalingaswami Fellow, she finds joy in mentoring students, dancing various styles like salsa, bachata, and swing, and reading fiction.

“I modelled how much time they would spend on different activities based on thermoregulation, how much energy they have at night, and various other behaviours. What we learned from that is that they spend a lot of their time perching, but they can also spend huge amounts of time just hovering and flying around,” Shankar said.

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Then she compared her own activity patterns with the audience, to help put the behaviour of hummingbirds into perspective. “Doing a PhD is a hard time, you’re wondering if you’re spending your time the right way. I started tracking what I was spending my time on through an app on my phone. I realised that I spent a solid one-third of my time, or eight hours every night, sleeping. I spent quite a bit of time just being alive and showering, I guess. I realised that my high-energy activity is mostly dancing. That was 5 per cent of my time and hummingbirds, by contrast, spend 22-84 per cent of their day in high-energy activities. So I don’t even go close to their minimum,” she explained.

Hummingbirds’ siesta

Shankar then introduced something really interesting: how hummingbirds go into a state of inactivity, called torpor, to save energy. “I wondered what hummingbirds were doing at night, because if they are using up energy so quickly and not feeding at night, then how do they stay alive? This is something people have been studying since the 1950s. They use a strategy called torpor, an equivalent of a deep slumber in common terms but physiologically not the same as sleep in humans. It is an inactive state where they are like, basically, useless,” she said.

She further explained that torpor is a bigger and broader term than hibernation. “The latter is a type of torpor, where you spend your time in torpor for more than a day at a time. Like being inactive for a week or a month. And what hummingbirds use is a daily version of that. They can use it just overnight to scale everything,” she said.

While displaying and running through pictures of hummingbirds she took from thermal cameras, she explained how as a scientist she was able to understand the varying body temperatures of these tiny birds while setting into and coming out of torpor. The session was quite a lively one, as attendees threw a volley of questions at her and she answered them all with mindblowing ease.

One of the most interesting questions included, “Why don’t they have a community-based strategy where a few of them are asleep and the rest are in torpor?” To this, Anusha replied, “We should suggest that to them,” and everyone laughed. She then clarified that hummingbirds are pretty solitary birds. “Some birds just don’t hang out together. They’re just like, I’m solo, and that’s how I’m going to live my life. They’re not communal or social,” she said.

When asked how salsa dancing helps her manage stress, she said, “I tend to overthink things in general, and partner dancing is one of the few spaces when I just zone out and am free just moving to music, and connecting with people. It’s the only form of exercise I enjoy - social exercise! I can feel myself shrinking if I haven’t danced for a while; I’ve been social dancing since 2012!”

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