Eric Masterson is no ordinary birdwatcher. An immigrant himself from Ireland to New England, he's fallen in love with bird migration - and specifically with a little-known wonder of the world that happens every spring and fall, just above our heads, under cover of darkness. To avoid hawks and navigate by the stars, millions upon millions of birds migrate at night, skimming over our rooftops while we sleep. To experience this invisible wonder, Masterson says, we have to learn to "see with our ears." Celebrating both avian achievement and human devotion, "Nightsongs" is a meditation on the art of seeing - and treasuring - what cannot be seen.