Airports typically worry about the weather causing problems to their smooth operations, and in fact, high winds, or a blizzard can be a threat to planes. There have been cases where wind drafts have caused planes to suddenly rise or drop hundreds of feet, and when this happens near the runway, it can get very dangerous.
Similarly, birds circling near the airport make the operators nervous, since a bird hit at those speeds can be dangerous, and also impact the engine of the plane. But, when was the last time you heard about an airport runway getting shut because of turtles on the runway ? That's right, those slow moving lovable animals that children also love. Any such movement on the runway can cause danger to a fast moving airplane, and when this movement of turtles is because of the need to lay eggs, you can do nothing but wait (link to article):
About 150 turtles crawled onto the tarmac at New York's John F Kennedy airport today in search of beaches to lay their eggs, delaying dozens of flights, aviation authorities said.
The slow-motion stampede began about 6:45 am, 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.
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 FAA said.