Why do Frightful's instincts finally tell her not to feed the eyases?

From the text:

Frightful ate the rabbit while the eyases watched, twisting their heads from side to side and calling “pseee” when she swallowed. Duchess walked up to her, screaming in earsplitting decibels. Then the eyas lifted her wings and attacked. Frightful backed off a few steps and stared at the young falcon. Lady and Drum lowered their bodies horizontally and charged Frightful. The eyases had become dangerous. They were practicing for the competitive world they would soon face. Frightful wanted no part of this schooling. She lifted herself into the air, fanned her wings, and flew to her tree stub.