The Effects of Roads on Populations of Small Mammals

(1) Trapping, observation and road mortality studies indicated that small forest mammals (e.g. Tamias striatus, Sciurus carolinensis, and Peromyscus leucopus-Rodentia) were reluctant to venture on to road surfaces where the distance between forest margins exceeded 20 m. (2) Wider roads were crossed almost exclusively by medium-sized mammals such as Marmota monax, Erethizon dorsatum (Rodentia), Procyon lotor and Mephitis mephitis (Carnivora). (3) Road mortality increased with increasing road improvement for medium-sized mammals and was highest when traffic density was high and young were emerging. (4) A four-lane divided highway may be as effective a barrier to the dispersal of small forest mammals as a body of fresh water twice as wide.