The Mandarin Duck is not native to North America although feral colonies have popped up in places resulting from ill conceived population introductions or escapees from collections. This is no different than the European Starling and Ring-necked Pheasant populations which were also introduced. Here's a list of ten introduced species.
Some species like the House Sparrow, European Starling and Rock Pigeon would likely have made it here in any case by hitching rides on grain ships or the like.
This male Mandarin Duck was and probably still is at Albro Lake, Dartmouth. I do not believe it can survive our winter unless recaptured or constantly fed.
The mandarin duck (Aix galericulata) is a perching duck species native to the East Palearctic. It is medium-sized, at 41–49 cm (16–19 in) long with a 65–75 cm (26–30 in) wingspan. It is closely related to the North American wood duck, the only other member of the genus Aix. 'Aix' is an Ancient Greek word which was used by Aristotle to refer to an unknown diving bird, and 'galericulata' is the Latin for a wig, derived from galerum, a cap or bonnet.
The adult male has a red bill, large white crescent above the eye and reddish face and "whiskers". The male's breast is purple with two vertical white bars, and the flanks ruddy, and he has two orange "sails" at the back (large feathers that stick up like boat sails). The female is similar to the female wood duck, with a white eye-ring and stripe running back from the eye, but is paler below, has a small white flank stripe, and a pale tip to its bill.
Both the males and females have crests, but the purple crest is more pronounced on the male.
Like many other species of ducks, the male undergoes a moult after the mating season into eclipse plumage. When in eclipse plumage, the male looks similar to the female, but can be told apart by its bright yellow-orange or red beak, lack of any crest, and a less-pronounced eye-stripe.
Mandarin ducklings are almost identical in appearance to wood ducklings, and very similar to mallard ducklings. The ducklings can be distinguished from mallard ducklings because the eye-stripe of mandarin ducklings (and wood ducklings) stops at the eye, while in mallard ducklings it reaches all the way to the bill.