Final answer:
The behavior therapist used systematic desensitization to reduce Mary Ann's fear of birds by exposing her to the feared object in a gradual, stepped approach paired with relaxation methods.
Step-by-step explanation:
The behavior therapy used to help Mary Ann reduce her fear of birds is called systematic desensitization. This behavior therapy involves gradually exposing a client to the feared object or situation, starting with the least frightening and moving towards the most frightening, while the client practices relaxation techniques to reduce anxiety. In the scenario provided, the behavior therapist first had Mary Ann relax and think of a bird, then showed her a picture of birds, followed by watching a movie about birds, and finally took her to an aviary. This is a classic example of systematic desensitization where exposure is increased incrementally, and paired with relaxation to overcome the phobia.