Dunn takes readers across the globe in pursuit of hummingbirds in The Glitter in the Green (Basic, Apr.).

What do you most want readers to know about hummingbirds?

In many cases, their population numbers have plummeted over the years. For example, the Juan Fernández Firecrown population is now estimated to number a mere 400 birds in the world, in one corner of a small island. We can’t necessarily attribute these declines to one simple causal factor—the real world isn’t always that neat and tidy. So what would I like readers to know about them? They’re wonderful, marvelous creatures, but they’re in trouble, and so too are the habitats in which they’re found, and the animals and plants with which they share those habitats. They’re the most colorful canary in the coal mine.

What did you learn about hummingbirds that surprised you most?

That Black Jacobins, a dapper black-and-white hummingbird found in Brazil, are singing at high frequencies beyond the range of human hearing and, indeed, that of most birds, too. It’s like they’ve got their own private frequency with which to communicate. If I learned one thing about hummingbirds as a whole, it was that there’s often more to them than meets the eye.

What was the weirdest behavior you observed?

That has to be the ability of some hummingbirds to enter a state of torpor. Hummingbirds that live in the Andes, in the zone above the tree line but below the snow line, survive the cold nights by allowing their internal temperature to cool, slowing down their metabolisms to save energy, entering a state of virtual hibernation—every single night of their lives.

To what do you attribute the worldwide fascination with the birds?

My theory is that we find something compelling about birds that often seem so fearless in our presence. Historically, we’ve projected positive qualities onto them—in folklore, they’re often selfless and helpful characters, or messengers between the realms of the living and the dead or between mankind and the gods. I wonder if now, when we’re all subconsciously aware that we’ve made a pretty dismal job over the years of looking after the planet and its biodiversity and have given wild animals ample cause to treat us with caution, we feel reassured by birds that don’t flee at the sight of us and, on the contrary, confidently go about their daily business in our presence.