The Great Egret is a heron which is native to the southern part of the United States and South America. It is a regular summer visitor to Central Park, which lies under a migratory path and has a characteristic "slowly-I-stalked" fishing stance that habitual visitors to the park should recognize. (The lake is kept stocked with fish for the benefit of these and other birds, and though human fishing is permitted, it is strictly on a catch-and-release basis.) A fish going down the bird's long neck is another familiar sight.
This photograph is probably from around 2001 and shows a relatively unblurred egret apparently "menacing" the blurry people sunning on the rocks below. (In reality, they were probably more startled than frightened, but this may amount to much the same thing.)
This was written for my 2008 Nu Mu [sic!] entry, but is also expected to go into the older Central Park Suite between "The Ramble" (the section of the park where this picture was taken) and "Angel of the Waters." Therefore it will be the fourth section of the Central Park Suite.