A species of parrot, it originates from the temperate to subtropical areas of Argentina and the surrounding countries in South America. Self-sustaining feral populations occur in many places, mainly in North America and Europe. Considerable numbers of monk parakeet were imported to the United States in the late 1960s as pets. Many escaped or were intentionally released, and populations were allowed to proliferate. By the early 1970s, M. monachus was established in seven states, and by 1995 it had spread to eight more. There are now thought to be approximately 100,000 in Florida alone.
The nominate subspecies of this parakeet is 11 inches long on average, with a 19 inch wingspan. Females tend to be 10 to 20% smaller, but can only be reliably sexed by DNA or feather testing. It has bright-green upperparts. The forehead and breast are pale gray with darker scalloping and the rest of the underparts are very light-green to yellow. The remiges are dark blue, and the tail is long and tapering. The bill is orange. The call is a loud and often considered unpleasant and along with their large communal nest that often obstruct power lines, these birds have bad reputation and are considered an invasive pest in Connecticut. Domestic breeds in colors other than the natural plumage have been produced. These include birds with white, blue, and yellow in place of green. As such coloration provides less camouflage, feral birds are usually of wild-type coloration.
In Connecticut they are most-often found along the shoreline in residential areas.