In 1890, a Shakespeare guild in NYC released 60 mating pairs of starlings to Central Park from England. Their goal was to introduce the birds from Shakespeare's writings, so that when they performed his plays in the park, the birds from his writings would be "on set" in the trees around them. This was long before ornithology was as popular as it is today. The short of the story is that birds migrate, and aren't bound to a specific area over time. Forever the opportunists, over the course of the next 50 years as they spread across the country, starlings pushed many native birds out of their habitats forever. Starlings are a communal, highly intelligent and historically opportunistic species, not unlike us.