When people that act the same, hang out together. People that have the same morals often tend to group. It has nothing to do with jealousy, nor the amount of friends a person is allowed to hang out with. It is NOT pointed towards having a close friend neither. it simply means when people act the same, they normally hang out. Like a clique.
Wondalee told someone something Maria told her not to tell anyone about.
Taylor told a boy something and brought up Ella's name, when Ella wasnt supposed to tell anyone but trusted Taylor.
Wondalee and taylor hang out on a daily basis
THEREFORE, taylor & wondalee, are birds of a feather that flock together(they were doing the same thing).... thus an average person would describe what they did using the saying "birds of a feather flock together"