Complex sentence: In the fall McIlhenny eventually set the birds loose to migrate south for the winter; and, as he hoped, the birds returned to Avery Island in the spring, bringing with them even more snowy egrets.
Split into simpler sentences: In the fall McIlhenny set the birds loose to migrate south for the winter. As he hoped, the birds returned to Avery Island in the spring, bringing with them even more snowy egrets.