South Korean officials are conducting an emergency safety investigation after 179 people died in the country's worst-ever plane crash on Sunday.
Moments before the flight was due to land, air traffic control issued a bird strike warning - an alert about the risk of colliding with birds.
The investigation will look to confirm if a bird strike did lead to the crash, or if other factors could have been involved.
A bird strike is a collision between a bird and an aircraft in flight.
They pose a danger to planes because jet engines can lose power if birds are sucked into them.
Bird strikes are very common.
In the US, more than 19,600 wildlife strikes were reported to the Federal Aviation Administration in 2023, the majority of which involved birds.
And there were over 1,400 bird strikes in the UK in 2022, only about 100 of which affected planes, according to data from the Civil Aviation Authority.
Bird strikes are very rarely linked to fatal plane crashes.
Engines could stall or shut down if birds are sucked into them, but pilots typically have time to account for this and make an emergency landing.
Pilots are trained to be especially vigilant during the early morning or at sunset, when birds are most active, according to aviation expert Professor Doug Drury, writing in an article for The Conversation this summer.
But deadly accidents involving bird strikes do happen.
Between 1988 and 2023, some 76 people died in the US after planes collided with wildlife, according to the FAA.
One notable incident is a 1995 crash near an Air Force base in Alaska. Some 24 Canadian and American airmen were killed after an aircraft collided with a flock of geese.
A bird strike also caused the famous "Miracle on the Hudson" incident in 2009, when an Airbus plane ditched onto New York's Hudson River after colliding with a flock of geese. All 155 passengers and crew survived.
The events were dramatised in the 2016 film Sully, which starred Tom Hanks as the plane's captain Chesley "Sully" Sullenberger.