I only saw the Rehoboth colony once, on a field trip for Don Messersmith's USDA Bird Life class (I am 
embarassed that I don't remember how long ago...) At the time, there was a fairly large communal 
nest in a residential neighborhood built around a telephone pole and adjacent tree. 

I vaguely recall Don saying that the residents in the neighborhood didn't like the parrots because A) 
they were extremely noisy, especially in the early morning and B) they gathered the twigs with which 
they wove their nest from people's ornamental landscape shrubs. I think the local power company 
had put up some kind of protection or platform that prevented the nest from contacting the wires, 
though.

Maybe the colony and/or nest failed because of local residents breaking up the "nuisance nest"?

I found an interesting article on Monk Parakeets as an "alien invasive" here:

http://invasions.bio.utk.edu/invaders/monk.html

The overall conclusion of the article seemed to be that the Monks aren't really a big threat to US 
crops or natives, since they prefer exotic landscape plantings and bird feeders, and are kind of cute...