The passenger pigeon ( Ectopistes鈥痬igratorius ) once migrated in flocks鈥痮f 3 to 5 billion,鈥痭umbers great enough to black out the sky, but by 1914, the last of its kind,鈥痭amed鈥淢artha,鈥 passed away at the Cincinnati Zoo. Martha had been the last passenger pigeon alive in captivity, while the last known wild...