Still others are particularly interested in the movements or habits of one species or group. It was discovered only about ten years ago that thousands of hawks and eagles pass over New York City on their way south each fall. During the fall of 1996 the Central Park group tallied 14,821 hawks, vultures, and eagles of a dozen varieties. Their tables can tell you what dates and what kinds of weather conditions are best for which species. Some of the best birding areas in New York owe their existence to human agency.
Central Park is the most celebrated example.
Frederick Law Olmstead did not have birds uppermost in his mind, however, and an ongoing conflict pits the Central Park Conservancy, which wants to restore Olmstead's plan in its full integrity, against the birders who delight in the weedy profusion of the overgrown Ramble. In the 1940s he seized the opportunity offered by Robert Moses's need to dispose of thousands of tons of fill from the excavation of the Rockaway subway line to construct a fresh-water pond surrounded by a doughnut of wooded upland in the midst of the salt tidal estuary of Jamaica Bay. Herb Johnson's creation is now an internationally famous refuge for both birds and people. On the other hand, New Yorkers have also destroyed much superb natural habitat in their city, such as the marshlands in Van Cortlandt Park, in the northern Bronx, that used to harbor rails and herons. An urban environment, inevitably, has limited space for competing uses, and successful bird species can interfere with human activity.