Birds of a feather flock together
A flock is a group or family of birds that have the same type of feathers. This proverb means that people like to spend time with others that are of the same sort or with the same interests just like a flock of birds.
This proverb has been in use since at least the mid 16th century. In 1545 William Turner used a version of it in his papist satire The Rescuing of Romish Fox:
“Byrdes of on kynde and color flok and flye allwayes together.”
Sarah: “Why does Tom always get into trouble like his brother?”
Susanne: “Well, you know what they say, birds of a feather flock together.”