The end of the movie mentions "all 16 geese including Igor", but there are a total of 17 geese including Igor. In flying scenes, 16 geese can be seen in the air while Igor remains on the ground or with Amy.
After Amy bashes the game warden with the popcorn bowl, Susan pulls one of the goslings from his hand. She is still holding it when Amy gathers up all the other goslings and runs into the bathroom with them.
Although a radar (like the ASR-7 shown at the Air Force Base) can hypothetically detect a flock of birds and an ultralight, it's unlikely. Their low reflectivity and slow ground speed (the support boat said they were going 21 knots, about 25 mph), the radar would "reject" the returns as clutter.