A young Brown Rat, Rattus norvegicus, expired in Prospect Park. A cosmopolitan species, found on every continent except Antarctica, these rats thrive in dense conglomerations of humans because we provide so much for them to eat, and such nice places for them to burrow.
Robert Sullivan’s Rats: Observations on the History and Habitat of the City’s Most Unwanted Inhabitants is the place to read about the critters, who may outnumber us here in NYC. Or not.
Backyard and Beyond 
I used to see rats almost every time I came to the park – now it’s rare. I don’t know if it’s due to the number of red-tailed hawks, or use of poison.