ONE LATE-AUGUST DAY, Nancy Lawson—or “The Humane Gardener,” as she is perhaps better known—was making a video about a spicebush swallowtail butterfly when something just beyond it in her Maryland yard caught her eye. A green heron was visiting a small pond Nancy had created not long ago—her first such encounter with the bird. (That’s one of her backyard ponds, above.) When I saw that video on Instagram it made me think of the late-March morning when I’d stood...

