It is often said that increased bird activity is due to the coming rain. Often, many birds flying in the sky can be seen before heavy rainfall. Do birds run from the rain because they cannot fly when it is raining?
Well, birds can fly when it rains, but it is much more difficult for them then, so most often, if they do not have to fly, they prefer to wait out the heavy rainfall. Birds can sometimes be seen flying in the rain, usually short distances in search of food. But there are definitely fewer of them.
You can imagine how difficult it can be to fly when a lot of raindrops are falling on us. However, it is not the drops that are the main obstacle for birds. During rain and storms the pressure drops most often, which makes the air less dense. Fewer air particles mean that the flight requires the birds to use more energy, which is tiring for them. Therefore, in the process it is much easier to observe birds sitting on branches or power lines waiting for the storm to pass on.