This strange curtain-like pattern created by birds flying in formation in the sky baffled locals who feared it might be an early sign of an oncoming disaster.

The puzzling sight was captured above the city of Panjin, in Liaoning Province, north-eastern China on December 6.

Phone footage shows the hundreds of birds flying so densely packed that it seemed as if a massive curtain was being drawn over the sky.

Residents suggested the birds seemed to migrate from the north, covering the sky in large numbers. Some claimed they were wild ducks that lived in the area.

According to experts, when birds fly in strange formations, it is typically aimed towards conserving energy.

Especially during migration, bird flocks tend to adopt various strategies to reduce energy consumption.

Forming a net-like pattern can decrease collisions and waste among the flock, making the entire group fly more efficiently. Additionally, this formation helps birds easily spot food and predators, enhancing their survival rate.