Rodent density indices from tracking tunnels, snap-traps and Fenn traps: do they tell the same story?

Comparisons were made of density indices of free-living populations of ship rats (Rattus rattus) in mixed forest in New Zealand by using footprint tracking tunnels and two kill-trapping methods. Tracking tunnels and snap-trap removal indices of rat densities showed similar trends when run on a 9 ha trapping grid, although immigration onto the grid occurred, thus violating one of the assumptions of the analysis.