Here's a report of a loose dog killing 50 rare birds in a Nature Conservancy preserve in Moloka'i. And why, dear TNC, do you think that the same thing isn't happening to migratory warblers, meadowlarks, sparrow and thrushes in New York City parks? Is it because the off-leash regulations say that off-leash dogs must not harm wildlife, and you are stupid enough to believe that either the dogs or their owners follow the regulations?
Just like they do in Prospect Park. I was there last Tuesday and had an interesting encounter in the Midwood. A woman was walking in the Midwood while her unleashed pitbull meandered along through the forest underbrush. She stopped to ask me directions. I politely pointed out that PEP officers and police had been giving out summonses for unleashed dogs in unsanctioned areas. She said she was aware but kept on talking. When she didn't leash her dog I remarked that she seemed unconcerned. She said that she intentionally brought her dog to places like the Midwood because enforcement would not find her there.
Here is a video of a couple playing with their unleashed pitbulls near the Vale of Cashmere. I assume that they chose that area between Nelly's Lawn and the Vale of Cashmere because it is somewhat out of view of any patrols.