Why don't swallows perch on trees?

Swallows have strong flying ability, but their legs are weak, so they often leave from a height and take off directly. If they live in trees, branches will hinder them from taking off, so they like to park in open places at any time.

When you see the swallows still moving outside when it rains, there are two possibilities: one is to catch insects that are wet by rain and have difficulty flying; Then swallows build nests with wet mud, which is more convenient to collect in rainy days. Of course, if it rains too hard, they will still take shelter.