This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Fans of science fiction are familiar with parallel worlds, existing beyond our awareness. Such worlds are real: my job requires peering into one. I study song sparrows.
These quintessential “little brown birds” are probably visiting your feeders right now. But their dull plumage disguises lives as complex as any soap opera, complete with thieving neighbors and usurping strangers, secret infidelities and public mate-swapping, untimely death and wayward young.
I follow these plot twists, studying their song and territorial disputes. For over a decade, I have documented their dramas by taking a variety of measurements and samples, and most importantly by placing bands on their legs to identify each bird on sight: one uniquely numbered U.S. Fish & Wildlife band, and three color bands. This is the story of a bird with blue and orange bands on his right leg, orange and “Fish & Wildlife” bands on his left: blue-orange-orange-fish, or BOOF, the bird who did everything wrong.
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In northwestern Pennsylvania, song sparrows follow a strict schedule. By March, males establish territories by singing above the shallow snow. Returning males set up shop where they lived last year, and newcomers replace the missing. Females settle down shortly thereafter, and nestlings begin hatching in mid-May. These young are fed by both parents until they become independent or (more commonly) are eaten by predators. Adults will then nest again and repeat until late summer.
But some males do things differently: like party crashers, they make their debut mid-summer, when the show is well underway—I call them “late arrivers.” Others—“movers”—switch to a new spot rather than reclaiming their previous territory. These late arrivers and movers were probably poor competitors, I thought, unable to succeed in early spring or defend their homes.
The day BOOF arrived, I was looking for a nest, tiptoeing comically through waist-high grass. Song sparrows here usually nest on the ground, nearly invisible under any available tussock. But as I considered which mound might be safely nest-free, I froze mid-step. Persistent singing percolated from the neighboring territory. Not occasional lazy mid-summer songs, but a relentless, insistent refrain. Some songs were longer and warblier than they should be. A battle had begun.
I had started nest searching because alarmed chirping, the sound of parents displeased with my presence, had alerted me to a possible nest on a territory where I hadn’t yet found one. But when my binoculars caught the chirper with a beak full of bugs, it wasn’t a bird who lived here. Instead, it was BBRF, owner of the disputed territory next door, and he was feeding a fledgling, not a nest. After stuffing food into the errant adolescent’s mouth, he rocketed away, singing, towards the commotion—where either neighbors or strangers were stealing his space during his moments of parental sacrifice.
I trailed BBRF to his territory. Three brown puffballs zigzagged between bushes, sometimes stopping to whisper songs through closed beaks, so soft I could barely hear. BBRF, four-year owner of this spot, fought two intruders while simultaneously trying to feed his fledglings, one of which had wandered territories away. Perhaps he simply couldn’t do it all. By the end of the day, the usurpers had divided his territory, singing unchallenged. Soon, they were banded and named: RWYF and BOOF. “Boof!” one of my students cheerfully called as the bird burst indignantly from my hand after banding. Late-arriving losers, I thought.
The following spring, as usual, some birds sang where expected; others were gone, replaced by new, naked-legged males. And a few, like BOOF, had moved. Hardly a surprise, if late-arriving and moving are both signs of territorial weakness. But BOOF fledged the first nest that year, and one of the first the year after that—a remarkable record of success. “Maybe,” my colleague suggested, “we should rethink these ‘losers’?”
Combining nine years of observations, we learn that nearly one third of males move at least once in their lives, and a quarter of new birds arrive late—occasional oddballs these are not. And birds like BOOF—late arrivers who subsequently move? These birds who do it all “wrong” are the most successful (measured in number of young fledged) of all. What I had assumed were signs of weakness may actually be alternative tactics: grab space when it’s easier (when other birds are busy parenting, for example), upgrade later.
You can’t answer a question you don’t think to ask. Our narrow assumptions of social simplicity and pathways to success in song sparrow world concealed a more complex reality, and I learned to always look more closely at animals who seem to be doing things “wrong.” But what of BOOF himself? Five years later, a strong storm swept through the site, flattening wide swaths of grass and snapping branches. BOOF’s tallest tree was broken at its base, and we never saw him again.