Tom good insights that do add value to many who have posted as to rat concerns on many forums for over 3 years now.
When we have several factors that are all increasing slightly simultaniously it does not take much tip of an additonal factor to cause a decline in an otherwise stable population.
Habitat, drought, gully washers, herbicides, otters, mink, coon, ferel cats, dogs, yotes and then the raptors day and night and a population that was in stability with a fur harvest can now drop to catistraphic levels or almost dissappear totally.
I need to prospect more and then review the localized spots of rat concentration to see what it is about that spot that holds the rats and keeps them from being over harvested.
Another thought if rats move less due to overhead fear (raptors) much like how deer change habits in the woods when wolves move in); does that make them more vulnerable to say mink, otter,coon and other preditors?
Also if males travel far more than females and the ratios are about equal would not more adult males find nesting females and may prey on the litters as another increased loss factor?
Pockets of rats when found can be really cleaned out fast by preditors, just as a small pond can be cleaned out by otter in short order.