I was down in Florida recently sitting at an outdoor cafe when I heard the familiar "chirp chirp" of a parakeet. Our family used to breed parakeets and they have a distinctive sound I'd recognize instantly.
The bird was sitting up on an electrical wire... he was a pretty cute little fellow and I tried to get a better photo of him head-on but he got spooked when I came nearby and flew away. He must have escaped from someone's cage and is probably lonely unless a mate escaped at the same time.
At one point in time there was a native parakeet in the United States called the Carolina Parakeet. Here is a summary of the parakeet from wikipedia. Too bad they didn't keep a few in captivity; apparently they bred pretty easily. Parakeets are pretty hardy birds so with only a bit of effort they probably could have kept a few around.
The part that saddens me the most is that when the hunters shot one of the birds the others would come down and congregate near their dead comrade, making it easy to get the rest of them. The birds were shot as pests or for their decorative feathers until the end when they were tolerated by man. No one knows exactly why they died off, apparently it was some sort of poultry disease. This is similar to what happened to all the crows on the North Shore of Chicago - the bird flu came through and devastated the population; it seemed like overnight all those giant, annoying and aggressive birds were dead.
An interesting movie about a related topic is called "The Wild Parrots of Telegraph Hill". This movie is a documentary about a loner who feeds and bonds with feral parrots living outside in San Francisco. Enough of the birds have escaped that they formed a mini-flock in the city. They have a lot of great scenes of the birds in the wild...