My 4 year old male Green Cheek conure was my only bird for a year. Thinking he needed a friend, we bought another green cheek a year later. We slowly introduced them and they have been around each other over a year. They have separate cages and sleep separately. When we let them out of their cages, the gravitate to each other. They immediately begin to preen each other. After a while, my male will aggressively bite my females tail. He will even step on her tail to keep her from getting away. How can I break him of this behavior?