Where did the Monk Parakeets on Amsterdam Avenue come from? Neither are banded, so they probably came from a wild colony in either New Jersey or Brooklyn.
The closest colony to Amsterdam Avenue, is in Edgewater, New Jersey. If a bird flew directly across the Hudson River it would arrive at around 138th and Riverside Drive going over the water for about a mile. (One of the unanswered question is do Monk Parakeets fly over large bodies of water?)
The nearest Brooklyn nest is about 8 miles away in Red Hook Park.
Monk Parakeets were seen in Central Park at various times over the last two years (see NYC Bird Report for details.) There have also been a number of reports from Riverside Drive this summer.
103rd Street is a great gateway between Central Park and Riverside Drive. Two blocks of 103rd are a pedestrian walkway through the grounds of the Fredrick Douglas Houses. It is also south of the 113th Street Cathedral Red-tails and north of the 96th and Broadway American Kestrels, so it may be a safe street for a Parakeet. Look it up on Google Maps. Or better yet, use Steve Baldwin's map of Brooklyn and New Jersey Parrots and scroll up and zoom into Amsterdam and 103rd, after selecting Hybrid mode to get a sense of the surroundings.
So, did these two come from New Jersey? Did the Riverside Monk meet up with the Central Park Monk? Who knows.