Lee,many years ago,when both Raptor and rat populations were high,we had one thing we dont today.About 10 times more rat habitat.
With the rat habitat dwindling,and our raptor population on the upswing,Rats never get a chance.
Most areas I trap,have huge Hawk,Eagle and Horned Owl populations.They just sit and wait for a rat to show its furry face.
Many of these ponds were good for 30 or 40 rats every season.It isnt chemicals that have done them in,as the farmers retired years ago.What is present in large numbers,that wasnt 20 and 30 years ago is Raptors.
So ponds that were good for dozens of rats year after year,are now good for 4 or 5,if you are lucky--still good cattails--just no rats.
Tom