There is, according to a building Porter a nest of hawks on the roof. One decided to enjoy a pigeon on the front lawn. Circle of life and all that.
Ms Rousseau of the Wildlife Conservation Society looked at the image and said "It looks like a juvenile red-tail hawk."
Here is a link to the wiki, with better pics.
At one time I carried a camera and took good images, now I carry a phone and take poor images. This is called progress.