The Effects of Roads on Populations of Small Mammals

Abstract

Little is known about the effects of roads on populations of animals. Pienaar (1968) summarized the possible effects of roads on organisms in a national park, but most workers have been concerned with mortality of animals along roadways (e.g. Simmons 1938; Knobloch 1939; Haugen 1944; McClure 1951; Hodson 1966; Evenden 1971; Bellis & Graves 1971). Roads affect many mammals by facilitating access to food or by increasing the food supply, but they may lead to damaging or fatal accidents. Bellis & Graves (1971) reported that Odocoileus virginiana* often fed on grassy road shoulders and as a result were frequently hit by vehicles. Taylor (1971) related the numerous skeletal fractures in east African viverrids to their habit of catching prey along roadways. In contrast, road verges provide a ready supply of grass and this has allowed some microtines to flourish and even expand their ranges (Baker 1971). In other cases, road verges provide important habitats for conservation of plants and animals (Anon. 1966; Kabat & Thompson 1963; Joselyn, Warnock & Etter 1968). However, roadside soil and vegetation are often contaminated by lead and other heavy metals used as additives in gasoline (Lagerwerff & Specht 1970; Smith 1971) and vegetation may be severely injured by high levels of sodium chloride (Hofstra & Hall 1971). Roads and railways have been found to inhibit the movements of feral Rangifer tarandus, but not those of domestic R. tarandus (Klein 1971). Studies of the effects of roadways on the dispersal of mammals are lacking although Buckner (1957) reported some data for Clethrionomys gapperi. This study documents the effects of roadways on the movements of small and mediumsized mammals (small mammals less -than 700 g; medium-sized mammals 700 to approx. 14 000 g) obtained from capture-recapture studies and from direct observation of roadways. The term road 'clearance' used in this paper, refers to the distance an animal had to move between forest margins to cross the roadway. Clearance may be equivalent to right-of-way, but this is not always the case.