On Wednesday morning, Rosie Copeland was out with her uncle Luke near Jackie Robinson Park in Harlem when they saw a crowd gathered near a chain-link fence, snapping photos. They went to see what the fuss was about.

“It’s a reindeer!” said Rosie, who is 3.

It was a deer, with one antler, coming right up to the fence, in a city park in Manhattan. The deer was practically posing for pictures.

Rosie’s uncle, Luke Metzger, who is visiting from Kentucky, was confused. “I kind of thought it was on display for the holiday, like maybe it’s some kind of petting zoo,” said Mr. Metzger, 23.

It is not a display. It is a wild animal.

For the past two weeks or so, an adult male white-tailed deer in apparently good health has roamed a strip of steep, rocky woods in the park, about 10 blocks long and no more than a couple of hundred feet wide.