At first glance it looks like a blizzard – but its in fact 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, PA, USA, 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.
His son Andrew Hoffman, who accompanied on the trip, said: “This was our first time witnessing the goose migration.
“When resting, all the geese will sit still on the water. Then they gradually get louder, lift off in unison and swoop around in waves. They were all snow geese. It’s a massive migration.
Afterwards, my dad was left wondering what keeps them from crashing into each other.”
Scientists have dubbed a term to describe the incredible and spontaneous coordination these birds display, calling it “scale-free correlation”.
The motion of flocks is not dictated by any one individual, but should any one bird change its course, its neighbours will respond sending the flock’s direction changing in an almost instant ripple effect.
Geese also fly in “v” formations to not only red wind drag, but the risk of colliding with one another.
Snow geese in particular are known as harbingers of the changing seasons. They fly south for the winter in huge, honking flocks that appear in V formation.
And after spending the colder months in southern coastal regions, they begin to migrate further north as snow melts – uncovering vital food sources on the ground and lake surfaces for them to land on.