The Hummingbird on West 81st Street New Yorkers weren't the only ones who enjoyed the mild winter this year. Thanks to the warm temperatures and absent flurries, a Rufous hummingbird called the American Museum of Natural History home, to the delight of museumgoers and staff members alike. Joseph DiCostanzo, an ornithologist at the museum, said that museum personnel first noticed the little bird flitting around the ornamental flowers outside the planetarium on Dec. 14. Hummingbirds usually clear out of the city by late October or early November, so the sighting raised some eyebrows. "A hummingbird in the city in December is odd," Mr. DiCostanzo said. The museum staff began to investigate the bird's identity and soon concluded that it was a Rufous hummingbird, a Western species associated with the Rockies. Normally, New York predominantly attracts ruby-throated hummingbirds on their way down south. Rufous hummers, on the other hand, are perhaps the most northerly nesters of the group, sometimes spending the summer as far north as Alaska. And they rarely stray as far east as New York on their way to Mexico, where they spend their winters. "That bird got itself lost to begin with," Mr. DiCostanzo said. In private, he said, he called the bird Rose, after the museum's planetarium building. As a bird both out of season and out of range, the Rufous hummer soon became the talk of the town's birders. "For a lot of local birders, this was their best chance to see a Rufous hummingbird without going to the West Coast," he said. The bird was not shy, either, and allowed photographers to approach within six feet. Some upstate birders made a special trip to the city just to see the Rufous hummingbird, and one enthusiast even set up a Twitter account about it, the museum's relates in its latest monthly newsletter. The bird spent the winter sipping nectar from museum flowers and sugar water from a feeder that the staff set up. Thanks to the species" hardy disposition, it was able to soldier through the few freezing nights the city experienced this winter, Mr. DiCostanzo said. Because winter's full fury never descended and food was ample, the bird probably did not have an incentive to leave, he added. "If we had had a normal winter, the hummingbird either would have moved on or succumbed to the cold, but luckily it didn't have to face that," he said. In the last couple of weeks, the bird has become more and more of a stranger to the museum, probably taking advantage of nearby early spring blossoms in Central Park. Mr. DiCostanzo said he last saw it on March 12, although someone reported a sighting last Tuesday. "At some point, it is going to move on," he noted. Bird sightings like this one may become less unusual: with increasingly mild winters ushered in by climate change, unseasonable animal visitors may become the norm. "We used to never get an emergence of the common grackle in the winter," Mr. DiCostanzo said. Now, there's flocks of grackles around Central Park all winter.