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Great Migrations

The biggest, strangest, and most surprising animal events we’ve found in this category—plus the reason they happen.

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See what happened.

Seasonal migration

Great Migrations

Millions of red crabs can take over Christmas Island roads

For a short period each year, roads, bridges, yards, and forest floors can become part of a mass journey to the sea.

Christmas Island, AustraliaChristmas Island red crab

Annual migration

Great Migrations

The river crossings that make the wildebeest migration look impossible

Huge herds compress into crossing points where movement, dust, water, predators, and panic collide.

Serengeti-Mara ecosystem, Tanzania and KenyaWildebeest

Spawning migration

Great Migrations

When a river fills with salmon moving upstream

A salmon run can transform a river into a moving corridor of fish, predators, and concentrated wildlife activity.

North Pacific watershedsSalmon

Marine migration

Great Migrations

The sardine run can turn South Africa's coast into a feeding frenzy

Tens to hundreds of millions of sardines can move along the coast, drawing dolphins, sharks, seabirds, and other predators into one moving spectacle.

South and east coasts of South AfricaSouth African sardine

Long-distance migration

Great Migrations

Millions of monarch butterflies can blanket forests in Mexico

North America's eastern monarch population travels thousands of miles south, eventually concentrating in mountain forests where huge clusters can cover trees.

North America to central MexicoMonarch butterfly

Seasonal bird migration

Great Migrations

Snow goose migrations can turn the sky white

Massive flocks of snow geese can gather over wetlands and farm fields during migration, creating a wall of birds, sound, and movement.

North AmericaSnow goose