About 150 turtles in search of beaches to lay their eggs crawled on to the tarmac at New York's Kennedy Airport, delaying dozens of flights, aviation authorities said.
The slow-motion stampede began at about 6.45am (10.45 GMT) on Wednesday, and within three hours there were so many turtles on Runway 4L and nearby taxiways that controllers were forced to move departing flights to another runway.
"We ceded to Mother Nature," said Ron Marsico, a spokesman for the Port Authority of New York and New Jersey, which owns the airport.
Workers from the Port Authority and the US Department of Agriculture were scooping up turtles and moving them across the airport, he said. Flight delays averaged about 30 minutes, the Federal Aviation Administration said.
The migration of diamondback terrapin turtles happens every year at John F Kennedy International Airport, which is built on the edge of Jamaica Bay and a federally protected park. In late June or early July the animals heave themselves out of the bay and head towards a beach to lay their eggs.
The peak of the migration usually lasts a few days, Mr Marsico said.
Several pilots, some of them stifling chuckles, began reporting turtles on Runway 4L just as the morning rush-hour was beginning at JFK, according to a radio recording posted on LiveATC.net.
"Be advised 30ft (10m) into the take-off roll, left side of the centreline, there's another turtle," called the pilot of American Airlines Flight 1009, a Boeing 767 that had just taken off bound for the Dominican Republic. "There's another one on the runway?" asked the controller. "Uh, well he WAS there," the pilot said as the big airliner climbed into the air.
American 663, a Boeing 737 headed to Fort Lauderdale, found its path to Runway 4L blocked by three turtles. After ground crews removed them, the plane taxied into take-off position, received clearance - and was promptly blocked by more turtles.
American and JetBlue, which has a hub at JFK, both said there were no major disruptions to their flights. "We hope for faster animals next time," JetBlue said in a statement.