What: Also known as Quaker Parakeets, Quaker Conures, Gray-breasted or Gray-headed Parakeets. They are colonial nesting parrots that build complex nests and live in them year-round. Unlike all other parrots, who are cavity-nesters, Monk parakeets build their own nests.

Originated from: Argentina, Brazil, Uruguay, Paraguay, and Bolivia.

How it arrived: Pet trade in the 1960s.

It's spreading: Into the US and Europe.

Damage: It is uncertain what the effects of this feral (returned to the wild after escaping from the pet trade) parrot will be in the US. In Argentina, it is considered a pest due to the damage it inflicts on crops.

Why it's a threat: This parrot has successfully naturilized in many places, including the temperate zone. This resistance could make it a potential threat.