In the world there is a huge number of the signs helping to predict future events on behavior of living organisms. Also swallows did not become an exception. In the people say: "Swallows low fly – by a rain". Whether there is a scientific justification to this belief?
Too romantic natures can claim that swallows are the unusual birds allocated with special intuition and an intuition they are capable to feel change of weather and the behavior to warn about it.
However everything is much simpler. It is enough to address a school course of physics and to remember the law of universal gravitation (F=mg) to explain behavior of swallows before a rain. Swallows are the birds of prey eating and bringing up the baby birds the smallest insects and midges a lot of living in air and not always noticeable to a naked eye of the person. Shortly before it is going to rain, the humidity of air considerably increases. As a result, settle the smallest drops of water on wings of insects. It leads not only to increase in weight of wings, but also to growth of body weight of the insect which activity, respectively, decreases. Midges, bugs are, etc. forced to fly below, than usually. Therefore also their persecutors – swallows - fall in the flight closer to the Earth's surface. The person not capable to see the true reason of similar flight of birds attributes to swallows unusual abilities and opportunities. But not only the coming rain can "force" swallows to change habitual flight altitude. Sharp temperature drops, for example an evening cold snap, result in the same effect. And again, the reason is in the changing at the same time, lower flight of insects. Therefore masterly, fascinating "dances" of swallows in the evening sky are not always bad weather harbingers. The younger generation of these beautiful birds often "rejects" the sign which became habitual. And even during a small rain it is possible to observe highly in the sky of the frolicing swallows. The fact is that uncharged production of youths food fulfill skill, new to them, – flight.