We did some disease studies on a series of farms in one state I lived in a few years back. Looked at norway rats and birds as vectors of industry leading causes of health issues. Spent several weeks doing night trapping and pellet rifle sampling from sundown to sunup and every time we came back to start the loop over at farm #1 from being at farm #5 we had full traps and were able to harvest another 50-60 with pellet rifles before moving to the next one.
Growing up we always had norway rats around the farm and d-con seemed to be the tool of choice, remember how well they burrowed from building to building.
Never saw the numbers though that I saw on that farm project, and when we returned positive results for the diseases folks took a new look at how they were or rather weren't managing the species tested.
The take home message to them was, if you have great bio security for your workers (boot washes on the way in, tyvek, gloves, etc..) and for your herd, but you had wildlife that were crossing boundaries back and forth from someone who isn't, you do not have a bio secure facility.
I do not however, miss performing necropsy on several hundred rats after a full night of sampling.
Out here I get wood rat (pack rat) calls more than any other. Hard to miss they are on site, have had pump rooms and other utility areas that are literally full of nesting material from their hoarding activity!
Justin