Simplify the following text for a Grade 8 native English-speaking person.
Original: The American Robin has an extensive range , estimated at 16 million square kilometers ( 6 million square miles ) , and a large population of about 320 million individuals .
Simplified: It is estimated that its range is 16 million square kilometers ( 6 million square miles ) . It is also estimated that there are about 320 million individual American Robins .