Around these parts, they are better know as Quaker Parakeets. They are very bright and hearty birds which are sold in the pet trade. They can mimic human speech. Their call sounds like a beeper pager to me.
When I visited south Florida, there some who had nested in the palm trees along the Atlantic beach.
They are illegal to own in some states because of their ability to escape into the wild and survive. They have no known native predators.
Hawks?