NEW YORK — Of all the factors that could delay flights at New York’s John F. Kennedy International Airport, this one is probably the slowest: turtles.

Nearly 400 diamondback terrapins have turned up on the airport’s property this year, most near the sandy turf bordering runways where they lay eggs and build nests. Some of the slowpoke visitors have managed to crawl onto the runways and taxiways, causing delays while workers round them up, the Port Authority of New York and New Jersey that operates the airport said.

While officials said they didn’t have information on whether a plane has ever hit a turtle, they did say that it’s not uncommon to have delays of several minutes while workers pluck turtles from the potential path of planes. The turtles are measured, tagged and returned to a safe habitat.

That normal habitat is the nearby Jamaica Bay salt marshes. But each year during a monthlong mating season that peaks in mid-July, they find special spots for their eggs to hatch, mostly along the perimeter of the airport.

Two years ago, barriers were installed to deter the turtles. But that doesn’t stop them all.