Why Birds Do What They Do
The more humans understand about their behavior, the more inaccessible their world seems.
Bushtits—almost impossibly tiny gray birds that live in flocks across the western United States—are not hard to spot in the Bay Area. I usually become aware of them by noticing a chorus of peeping in part of an oak tree that seems to be jiggling. Their nests, though, are well hidden, and they’re different from what most people would expect. Made out of spiderwebs, fur, lichen, and plant material, they hang down from a couple of branches like a strange-looking sock with a side entrance near the top. A month or so ago, when my friend Joe showed me the nest he’d found, we watched the birds ferrying bits of fuzz and what we speculated were oak flowers, adding them thoughtfully to the growing blob.
Bushtits were some of the first birds I learned to identify when I started bird-watching, in 2016, armed with what seems to be the standard guide in these parts. Sibley Birds West features two species to a page with a brief description, different molts, and subspecies—all written and illustrated by David Allen Sibley, widely considered the successor to Roger Tory Peterson, who invented the modern field guide. But in the years since, I’ve become aware of how much is left to learn about the birds I thought I knew. To observe birds not just as instances but as actors is bird-watching in time, whether I’m observing moment-to-moment decisions or changes across the seasons. As if anticipating my curiosity, Sibley has now produced a different kind of book, What It’s Like to Be a Bird, whose cover promises it will explain “what birds are doing, and why.”
I had been reading the book when Joe pointed out the nest, and soon I started seeing nests everywhere—dark, enigmatic shapes hidden in the leaves, like tiny versions of the alien ship from Arrival. Luckily for me, a full page in Sibley’s new book shows the step-by-step construction of the bushtit nest, starting with a skeleton of spiderweb stretched across branches, which is then gradually filled in and deepened. One day in a parklet near my house, I strained to see two bushtits on step one of the building process, the faintest spiderweb ring connecting two twigs. I got excited. The birds were doing something! Meanwhile, a ground squirrel crashed clumsily through the tree, and when it got too close to their fragile creation, the bushtits changed from their usual peeping to an alarm call.
Unexpectedly caught up in this battle for existence in a small oak tree, I found myself wanting to join in the alarm and shoo the squirrel away. Feeling the bushtits’ frustration (or so it seemed) made me think of the surprisingly tender preface to Sibley’s book, in which he writes that instinct is more than merely programmatic: Birds must be motivated by something like feelings. “I realize this is enormously anthropomorphic,” he notes, but nevertheless, “maybe the feeling an oriole has when looking at its finished nest is similar to the feeling human parents get when we look at a newly painted and decorated nursery. Maybe the chickadee ‘sleeps well’ after a good day of gathering and storing food for the winter.”
The anthropomorphizing caveat points toward the mental, even emotional, reach that is always happening when we try to imagine “what birds are doing, and why.” In his 1974 essay “What Is It Like to Be a Bat?,” the philosopher Thomas Nagel famously argued that answering this question is impossible because the differences between us are just too great:
Even if I could by gradual degrees be transformed into a bat, nothing in my present constitution enables me to imagine what the experiences of such a future stage of myself thus metamorphosed would be like. The best evidence would come from the experiences of bats, if we only knew what they were like.
Sibley is undaunted. Describing what scientists have discovered about the vision of a snipe, he asks us to “imagine being able to see the entire sky and horizon, and some detail along most of the horizon, without turning your head.” Birds also process images more than twice as fast as humans do; Sibley speculates that our movies would look like slideshows to them. To explain the way that warblers and other birds use the magnetic field to navigate, he has to portray an entire sense that humans don’t have, using “a totally hypothetical artist’s rendering of what the bird might see in the sky”: a domed band of polarized light, crossed with another oriented with the magnetic field.
In all this struggling to imagine, I encounter a certain irony: The more I know about birds, the more inaccessible their perceptual world seems to me. From Jennifer Ackerman’s The Bird Way: A New Look at How Birds Talk, Work, Play, Parent, and Think, I learned that birds such as the vinous-throated parrotbill and the black Jacobin hummingbird make sounds beyond our range of hearing, while the mating displays of male black manakins feature a “high-speed somersault” so fast that humans can see it only in slowed-down video. Birds see colors that we never will, and distinguish among colors that look the same to us. Writing about how they interpret a wall of foliage as “a detailed three-dimensional world of highly contrasting individual leaves,” Ackerman laments that she has tried to see what birds see, but humans just can’t differentiate among the greens.
Learning more also means having more questions. Both books include recent research that illuminates new behavior, whose mechanics and purpose remain hypothetical or totally unknown. Ackerman writes that veeries, a type of North American thrush, can anticipate hurricanes months in advance, adjusting their nesting and migration schedules accordingly—but the way they do it is a “deep mystery.”
One unforgettable example comes from the greater ani, a South American species of cuckoo. As Ackerman explains, greater anis form genetically unrelated co-parenting groups that stay together for a decade or more; choosing a nest site and building the nest are cooperative efforts. The females all lay eggs at the same time and are incapable of recognizing any particular egg as their own. Throughout the day, the birds will gather into what Christina Riehl, a Princeton ecology and evolutionary-biology professor, calls “a giant football huddle,” bringing their beaks close together and emitting a strange gurgling sound for 10 minutes or more. Somehow the gurgling is part of the communication needed to make complicated group decisions, but Riehl tells Ackerman that she is unsure of the specifics. “How do individual birds ‘vote’ in these collective forums?” she asks. “How do they overcome disagreements and conflicting opinions?”
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On YouTube, I was able to track down only one video of this gurgling, which was taken by Priscilla Diniz in Manaus, Brazil. It’s called “Crotophaga major / Anu-coroca / Greater Ani,” and I have probably watched it 50 times now. Three anis sit in a tree, their heads close together, making a sound that a viewer might attribute to some kind of background noise until they all stop, rearrange themselves, and begin again. As they make the sound, their bodies vibrate slightly, like an old car that’s just been started up. They inch closer together, cocking their heads slightly, seeming (from my anthropomorphic view) to be listening attentively to one another. At some point a fourth ani arrives and joins in the vibrating and gurgling. Every time I watch this video, I can barely believe that what I’m seeing exists on Earth.
But this strangeness exists even in our backyards. My imagination is stretched every morning by the neighborhood crows that I befriended on my street in 2016, after learning in Ackerman’s previous book, The Genius of Birds, that they recognize human faces. I’ve had four years to observe the behavior of one crow family. I’ve seen them groom one another, forage in the neighbor’s roof gutter, peck curiously at mushrooms, wipe their beaks on the power line, yawn, scold a hawk or cat (with different sounds for each), do barrel rolls when it’s windy, and sometimes follow me down the block, landing on various branches near my head. Lately they seem to enjoy my hiding a peanut for them under a pile of driftwood and pine cones, and they once moved a small rock from one side of my balcony to the other. Why they did this is … a deep mystery. The more I observe them, the less of a grasp I feel I have on them. Instead, they look more and more like willful individuals.
The crows also remind me that while birds and humans may see different worlds, we inhabit the same one, our alien universes stitched together at the point of contact, continually influencing each other. One day, overjoyed to find a bushtit nest down the street from my house, I realized that a scrub jay was watching me. Scrub jays, part of the same family as crows, are known to possess something like theory of mind, the ability to imagine what another animal is thinking. When burying a snack, if a scrub jay sees another jay watching, it will pretend to finish burying it, then come back and rebury it later. Jays also eat bushtit eggs. Noticing the scrub jay, I scurried away, thinking it might have used my behavior (stopping and staring) to locate the nest.
Birds respond to human behavior in the long term, too. Ackerman writes that zebra finches, facing a warming climate, have a way of communicating an instruction to their unhatched young to hatch smaller so that they lose heat more easily. Sibley notes that scrub jays are nesting five to 12 days earlier than they did 100 years ago, probably to align with plant and insect cycles affected by climate change. Some birds in urban areas have ramped up nighttime singing in response to increased daytime noise, and birds living in loud places have shifted the pitch of their songs higher in order to be heard. Of course, behavioral flexibility can go only so far. In September 2019, Science published findings that North America had lost close to a third of its birds in the past 50 years. One of birds’ broadest responses to human behavior, it turns out, has been to vanish.
There’s a large cemetery not far from where I live. For now, thanks to the abundance of trees and ponds, this area of rolling hills hosts an amazing variety of birds. Next to one of the ponds is a coast live oak tree and a grassy ledge where I like to sit and lie back. From there, I can look into the branches of the oak, waiting for the arrival of others. I have seen oak titmice, chickadees, house finches, goldfinches, white-breasted nuthatches, brown creepers, yellow-rumped warblers, Townsend’s warblers, western bluebirds, ruby-crowned kinglets, black phoebes, Bewick’s wrens, white-crowned sparrows, golden-crowned sparrows, California towhees, scrub jays, Steller’s jays, Cooper’s hawks, ravens, acorn woodpeckers, and, yes, bushtits.
When I was once telling a friend that this was my favorite way of bird-watching, I said something about how “it’s as if I’m not there at all.” We laughed ruefully at how this sounded: me on the ground in the cemetery, not moving, surrounded by graves. Besides being a genuinely good way to see birds, it was also a form of self-erasure—as though only by imagining myself to have exited the living world could I absolve myself of being human, the species responsible for the demise of birds and so much life on Earth. The wish to disappear was a wish for bird-watching without the watching: just birds.
Ackerman mentions an “only partly tongue-in-cheek” speculation offered by Mathias Osvath, a cognitive-science researcher who works frequently with corvids. These birds have learned to use human civilization for food and shelter (for example, memorizing the schedule of garbage trucks), and Osvath says that if we were to disappear, the selective pressure might push them to become superintelligent, “the next big thinkers.” There’s a calm comfort in imagining a crow society devoid of humans. But I can’t let myself rest there. I must get up from my spot in the cemetery and return to the present, where the experiences of birds and humans are entangled, where our behavior matters.
I can imagine more people reading about bird behavior and starting to see birds as intentional actors bearing rights, rather than decorative or entertaining automatons. And if I really try, I can stretch my imagination even further. In Re-enchanting the World: Feminism and the Politics of the Commons, Silvia Federici writes about refusing a political and economic “state of irresponsibility” in which “the production of our life inevitably becomes a production of death for others.” Trying honestly to envision a world in which there are still birds left for us to watch means thinking about how bird-watching can never be an idle or apolitical hobby, insofar as I’m watching the lives of others on this imperiled planet where I also live.
At times, I want to give up, dissolve into the cemetery grass. But the birds are always there, drawing me out and upward. Different though we may be, I think I do know one part of animal experience firsthand: this curious “life-y-ness” of life, which wants to go on, even to proliferate. I watch the crows gathering big beakfuls of grass from a dry patch across the street to line a nest for their young. I find a perfect cup-shaped hummingbird nest in a bottlebrush tree, and watch a discerning raven transporting certain sticks (but not others) to the top of a redwood. Joe texts to say that the bushtit nest has become a perfect L shape and that its two architects have settled down inside it. With every new generation of birds, my feeling of responsibility deepens. They remind me of what I’m doing, and why.