Why are seagulls called "weathermen"?

Seagulls feed on coastal insects, mollusks, crustaceans and worms and grubs in cultivated land; They also prey on small fish on the shore and pick up leftovers discarded on the shore and on ships. Some large seagulls prey on eggs and young birds of other birds (including their own kind). Seagulls are the most common seabirds. In the coastal areas, seaports and fishing grounds rich in fish and shrimp, flocks of seagulls float on the water, swimming, foraging and flying at low altitude, and like to cluster in food-rich waters. In addition to eating fish, shrimp, crabs and shellfish, seagulls also like to pick up leftovers discarded by people on board, so seagulls are nicknamed "harbour cleaners". Ports, docks, bays and ships are almost frequent visitors. On the ship's route, seagulls will follow, and even walking on the beach at low tide will wake up a group of seagulls. Seagulls are also "forecasters" of maritime navigation safety. Sailing on the sea by boat, you will often run aground because you are not familiar with the water environment, or be shipwrecked because of sudden weather changes. Experienced sailors know that seagulls often land around shoals, reefs or reefs, and flocks of seagulls fly around and make noise, which is undoubtedly a signal to navigators to avoid collision with reefs; At the same time, it also has the habit of flying in and out of the port. Whenever navigation is lost or foggy, observing the flying direction of seagulls can also be used as a basis for finding ports. In addition, if seagulls fly close to the sea, the weather will be good in the future; If they wander along the seaside, the weather will get worse gradually. If seagulls leave the water and fly high, flying from the sea to the seaside in droves, or flocks of seagulls gather on the beach or in cracks in rocks, this indicates that a storm is coming. Seagulls can foresee storms because their bones are hollow and tubular, and they are filled with air without bone marrow. This is not only convenient for flying, but also like a barometer, which can predict the weather changes in time. In addition, the hollow feather tubes on seagulls' wings can feel the change of air pressure sensitively, just like a small barometer.