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Mass Gatherings

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

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Flocking event

Mass Gatherings

When thousands of starlings turn the sky into a moving shape

A murmuration can look like smoke, a wave, or a single giant organism changing direction in midair.

Europe and other starling rangesStarling

Evening emergence

Mass Gatherings

What it looks like when a cave releases a river of bats

At major roosts, bats can pour into the evening sky in a stream that seems to keep going long after sunset.

Major cave and bridge roosts worldwideBats

Mass spawning event

Mass Gatherings

When hundreds of thousands of horseshoe crabs cover Delaware Bay beaches

Every spring, Delaware Bay beaches become spawning grounds for enormous numbers of horseshoe crabs, creating one of the East Coast's strangest seasonal wildlife spectacles.

Delaware Bay, Delaware and New JerseyAtlantic horseshoe crab

Mass nesting event

Mass Gatherings

When sea turtles nest together in synchronized waves

Kemp's ridley sea turtles are famous for arribadas, mass synchronized nesting events that can suddenly fill beaches with nesting females.

Gulf Coast nesting beaches, especially Mexico and TexasKemp's ridley sea turtle

Seasonal den emergence

Mass Gatherings

Tens of thousands of snakes emerge at the Narcisse dens every spring

Manitoba's Narcisse Snake Dens erupt with red-sided garter snakes each spring as enormous numbers surface from winter dens to mate.

Narcisse, Manitoba, CanadaRed-sided garter snake

Synchronized mating display

Mass Gatherings

Thousands of fireflies can make an entire forest flash together

For a short period each year, synchronous fireflies in Great Smoky Mountains National Park coordinate their flashes into one of the strangest nighttime wildlife displays in North America.

Great Smoky Mountains National Park, TennesseeSynchronous firefly