It’s a sunny Saturday afternoon, and Beatrice, Gertrude and Zelda, three butterscotch-brown Buff Orpington hens, are having a field day in Jennifer Carlson’s Seattle back yard. A landscape designer and organic gardening expert, Carlson has placed a floorless chicken coop––or “chicken tractor”––on her lawn, where the hens methodically search for bugs and worms, taking an occasional break for a dust bath. Once the birds have excavated one area, she moves the tractor to a new piece of turf.

The remains of the chickens’ excavations—a rich mixture of dirt, chicken manure and grass that’s sprinkled with oak leaves to help decompose the droppings—gets a second life as compost for Carlson’s organic vegetable garden, which features basil, raspberries, eggplant and heirloom tomatoes. “The vegetables we grow then provide scraps for the birds, who produce delicious eggs and great compost for the vegetables,” explains Carlson, who has raised chickens in the city since the 1980s. “It’s a really cool cycle.”

Carlson, who spent her early childhood among Wyoming and Colorado ranchers, now lives in a cheery red house on a corner lot in Seattle’s Magnolia neighborhood. “Chickens make ideal pets,” she says. “They like being around people, and they’re very curious, comical and ungainly. Yet they’re contained, so they’re not chasing the mailman.” With a cup of coffee in hand, she makes a daily round of the garden every morning. “It’s relaxing seeing the chickens and garden thrive.”

“I make the mistake every now and then of ordering an egg dish at a restaurant, and I regret it...