For me I am one that is not as concerned about predators, chemicals, erosion etc. as many are. We were drier than normal for many years prior to 2018 and our ditches, most sloughs etc. were dry or only mud and our rat numbers declined. We had 3 wetter than normal years, a couple about 10 inches above normal and last year we had rats in every ditch and slough. The predator numbers actually should have increased due to more food and the fact that land trapping and water trapping are way below the norm. There were no changes in crops or chemicals or herbicides. We actually had more flooding, but still had more rats. I trap a lot of area that has very limited cattail habitat and thus fewer rats and smaller rats typically, but I am concerned regarding the continuing changes in the cattail type and abundance. For me where I trap it is still almost all about available water. We have been using herbicides since the mid 1960s and the Mid West had some big rat harvests over those boom years. The one thing about raptors is they don't routinely kill multiple prey per hunt like some other species do.
The other factor for my area is rivers and creeks versus larger marshes. A river is really two edges and predators hunt edge and everyone that walks, flies and swims can cover the edge easily. A large marsh is another whole issue. Many rats may be preyed upon but there is just so much more area for the rats to be that predation pressure is less, plus the water levels tend to be more stable.
Bryce