A good Integrated Pest Management (IPM) rodent program starts with inspection. A good inspection provides four valuable pieces of information: what is present, the extent and severity of the infestation, the location of rodent harborage and high-activity area, and the safest and most efficient control strategies.
First identify key sources of exterior rodents. For Norway rats, look for tall grasses or low-lying landscaping near buildings, water sources (i.e. ponds, drainage ditches, decorative fountains, etc.), food sources (dumpster, trashcan, garden, etc), and shelter/cover from predators (i.e. junkyards, infested neighboring properties, city sewer systems, etc). Next, identify rodent entry areas (i.e. utility lines entering the building, spaces beneath doors, unscreened vents, etc). Lastly, look for high-activity areas, typically near food sources, by searching for fresh fecal pellets, gnawing damage, runways/tracks/grease marks, borrows, and urine stains. It may help to conduct night inspection, use black lights or flash lights, use tracking patches, and/or video cameras (Corrigan, Robert M., and Dan Moreland. Rodent Control: a Practical Guide for Pest Management Professionals. GIE Media, 2001).