At first glance it looks like a blizzard - but in fact it's a mass migration of over 100,000 birds. Every year in late-winter, snow geese, tundra swans and Canada geese descend on Middle Creek Reservoir in Lancaster County, Pennsylvania, as they head back north for spring. Spectacular footage shows the eye-opening sight as thousands of squawking birds move in unison. William Hoffman, from Oreland, PA, captured the images during the migrations peak in late February.