Why do swallows fly low when it's about to rain?

Why do swallows fly low when it's about to rain?

The main reasons are:

1. Before the rain, the air pressure in the sky was relatively low, and the flying insects flew very low. Swallows eat small insects to prey on these flying insects. Before the rain, the air was humid, and the wings of insects became heavy because of the humidity and could not fly high. Swallows have to fly very low to catch them.

When it's about to rain, the air is turbulent, and swallows always fly up and down, up and down.