Spring migration is a birder’s Christmas Morning. It’s a birder’s Happy Hour after work on a Friday. It’s a birder’s Embrace with Loved Ones in the Airport After a Long Journey. The wait is over and we can stop pretending we actually enjoy standing in the freezing wind looking at gulls. As you read this, millions of birds are winging their little bodies north from the tropics, and for many American birders, the most yearned-for of these birds are the warblers. Warblers are the gems of American birdlife. Unlike warblers in the rest of the world, which are mostly brown and boring-looking (and not actually closely related to our local birds), our New World warblers, or wood warblers, are tiny bursts of color. Bright yellows! Oranges! Greens and blues! Each of the 50-or-so species regularly found in the U.S. has its own color scheme, vivid and delicately patterned, like a fluttering Easter egg. They’ve been away because they’re insect eaters, and the States...