One of the few negatives to photographing in a marsh or swamp is the lack of open space. At the shore or in fields we can see a bird coming and have time to pan and swing the camera with the bird. In a swamp you try for an opening in the trees and time everything for when they (should) appear. In general a boat load of junk is what you get.
Sometimes they appear on time and (with luck) slow enough for an in flight photo.