Swallows feed on insects. Swallow is a migratory bird widely distributed in China. They fly from the south to the north in spring and return to the warm south for winter in autumn. Because they are numerous and like to nest under the eaves close to people, people are familiar with them and like them very much. Swallows' bodies are streamlined and fly faster. They have scissors-like tails, which can quickly adjust their flying posture and catch flying insects efficiently in the air.
Second, the air pressure drops before it rains. Before it rains, due to the action of airflow, the air pressure in the area that is about to rain will drop slightly. When the air pressure is low, the air becomes thin and the oxygen content also drops. Because of the decrease of oxygen content, many small flying insects, such as dragonflies, usually stay at half altitude, gather near the ground, and swallows fly low to prey. Some insects that live in the soil crawl out of the soil to get some air because of the decrease of air pressure and the increase of humidity. This is a good opportunity for swallows to feed, so swallows often fly very low to catch them.
Third, it will rain when swallows fly low. In addition, insects that usually live in the soil will climb out of the soil to breathe air because of the temperature drop. When many insects fly down slowly, it is a good time for swallows to hunt. Therefore, swallows have been dispatched, often flying at low altitude, and accurately catching their own food. After a long period of research, people have formed a reputation? Will it rain when swallows fly low? Meteorological proverb.
Dear readers, do you understand the principle of this meteorological proverb?