"The most common type of bird seen in this area is the Red-Bellied Woodpecker." This is correct because it provides specific information regarding the topic, i.e. birds along the east coast.
"The eastern coast of the United States is home to over 1,000 species of birds." This is incorrect because it would most likely act as a topic sentence.
"If you travel along the east coast, chances are that you’ll spot several flying friends along the way." This is incorrect because it would best serve to introduce the topic.
"Not only do people come to watch the birds, but they also photograph the birds they see." This is incorrect because it would best serve as a transition sentence, leading to more details about photographing birds.