In the 230-acre forest beyond steve kelling's wall-to-wall office windows, 50 species of migratory birds—warbling vireos, rose-breasted grosbeaks, cedar waxwings—have arrived overnight. On this early May afternoon their calls ring through the forest in a giant songbird mash-up. How Kelling, or anyone here at the Cornell Lab of Ornithology in Ithaca, N.Y., can concentrate on work is a mystery.
Of course, the scene beyond the window is the work. Kelling pulls up an animated map on his laptop. It is the U.S., etched in white against a black background. A bar below the map shows the passage of time, a year in total. At first, nothing happens. Suddenly, around April, a burst of orange appears in southern California. It spreads like flames to the north and east, until the entire western third of the country is ablaze, glowing and flickering in various shades of orange and white. Then it reverses, the color vanishing from north to south, until, by November, the whole map is dark again. We have just watched the annual migration of the western tanager.