The Impact of Roads on Large Carnivores Around the World

Deep in the oak and birch forests of the Sikhote-Alin State Biosphere Zapovednik, a Siberian tiger quietly stalks a herd of sika deer. She is one of the fewer than 400 remaining members of this wild subspecies, Panthera tigris altaica, and is lucky to live in pristine, unfragmented habitat in the Russian Far East where she finds lots of prey and few humans. Habitat loss, fragmentation, and poaching have already led to the extinction of three out of eight tiger subspecies worldwide. A recent study by the Hornocker Wildlife Institute and the Wildlife Conservation Society, however, has identified something that threatens even this relatively healthy Russian population - roads.

Although only a single paved road, built in 1972, winds through the eastern edge of the reserve, researchers are becoming increasingly concerned about its impact on the tigers. In a study published in Conservation Biology, Kerley et al. (2002) report that tigers whose territories are crossed by this primary road were more likely to die and less likely to breed.

In fact, all four adult female tigers monitored in this area were eventually killed by poachers. Furthermore, no cubs born to the poached tigers lived long enough to disperse into their own territories, presumably because they were poached themselves or hit and killed by vehicles. The authors suggest that although this area of the reserve has high-quality habitat and full protection from public use, the construction of the road has resulted in high mortality and low reproduction and a net loss to the population of tigers.

Large carnivores are one of the most endangered groups of animals, in part because they are highly susceptible to the detrimental effects of roads. Large carnivores are inherently rare, lmost always require huge home ranges, and often compete with humans for food resources. As a result, many carnivores have been eliminated from most of their historical ranges.

Where carnivores persist, they are constantly threatened by roads and their effects, which include direct and indirect mortality, habitat fragmentation, population isolation, and ultimately the loss of habitat outright. Here I review how these various impacts are affecting carnivore populations worldwide, and recommend possible solutions.

Direct Mortality

Direct mortality from vehicle collisions is one of the most obvious and well documented effects of roads on large carnivores worldwide. In the Bow River Valley of Canadaøs Banff National Park, roadkill was the primary cause of mortality for wolves (Paquet 1993). Cougars in the same area have suffered a mean population loss of 3-5% due to road and train mortality (Gibeau and Heuer 1996). In Slovenia, 96% of Eurasian brown bear mortalities are caused by humans (Adamic 1997); in 1997 alone, five bear fatalities were recorded on one 30-km stretch of highway.

Following the reintroduction of the European lynx in the 1970s, 83% of lynx mortalities in France were human-caused, and half of these were from collisions with vehicles or trains (Stahl and Vandel 1999). Similarly, 75% of the mortality among the endangered Iberian lynx stems from human-caused factors including road accidents (Ferreras et al. 1992). Even the large carnivores of Tanzaniaøs Mikumi National Park have suffered from the construction of a single highway. Between 1973 and 1988 lions, spotted hyenas, jackals, and a leopard were all recorded as being struck and killed by vehicles (Newmark et al. 1996).

Indirect Mortality

Another major impact of roads is that they facilitate human access into otherwise untouched large carnivore habitat. This access increases illegal poaching and other negative interactions. Jensen et al. (1986) found that wolf populations in Ontario, Canada only persisted when road densities were low. When more than 0.6 km of roads existed per km2, wolves were trapped and shot in significantly higher numbers. Demarche (2001) predicted that the construction of an allseason road in western central British Columbia would have a significant impact on grizzly populations because of increased humanbear interactions and subsequent increased bear mortality. The Iberian lynx, although critically endangered and federally protected, also continues to be illegally trapped and killed in Spain (Ferreras et al. 1992).

Avoidance and Fragmentation

Roads and other linear networks can act as barriers for large carnivores and prevent dispersal, while the avoidance of roads can often lead to the fragmentation and isolation of carnivore populations. Isolated populations can exhibit increased demographic fluctuation, inbreeding, loss of genetic variability, and ultimately local extinction.

An accumulation of obstacles including roads has delayed the expansion of the recovering wolf population in northern Spain (Blanco 2001). Jensen et al. (1986) concluded that high road densities on the border between Ontario and Michigan prevented wolves from recolonizing former habitat in the U.S. The Trans Canadian Highway in Banff National Park has been shown to act as a barrier and restrict wolvesø ability to disperse across their existing range (Paquet and Callaghan 1996). And during a five-year study in this same area, only two radio-collared male grizzly bears regularly crossed the hightraffic, year-round road, while none of the radio-collared females did (Gibeau et al. 2001).

Inshida (2001) suggested that road construction acted as a barrier and indirectly fragmented a population of Japanese black bears. Recent road construction has blocked potential corridors important for the dispersal of Eurasian brown bears from the Dinaric Mountains in Slovenia to the Alps (Kobler and Adamic 1999). Rodr¦guez and Delibes (1992) also were concerned that the construction of highways, large dams, and high-speed railways in Spain may further restrict Iberian lynx movements, increase fragmentation, and increase the risk of mortality.

Habitat Loss

The ultimate result of the cumulative effects of roads and attendant human disturbance is the loss of habitat. Roads often prevent large carnivores from reaching portions of high-quality habitat that they would otherwise use. In fact, road density is often used as a surrogate in predicting carnivore habitat suitability. Paquet and Callaghan (1996) reported that the combination of obstruction, alienation, occlusion, and mortality reduced the ability of the Bow River Valley of Banff National Park, Canada to support wolves.

Roads are often precursors to development, which further degrades carnivore habitat. For example, a highway recently constructed in Nepal has severely reduced the quality of large areas of tiger habitat. Villagers who once gathered only a single load of wood now gather several bundles to sell to passing truck drivers. This increased harvest has accelerated forest degradation, decreased the number of ungulates, and led to the local extirpation of tigers (Smith et al. 1998).

Solutions and Conclusion

How do we save our last large carnivores from global extinction? Traditional techniques for mitigating the direct effects of roads, including wildlife tunnels and overpasses, are being developed in Slovenia (Kobler and Adamic 1999), Japan (Ishida 2001), and Canada (Gibeau 2001). These techniques, however, are often limited to wealthier nations from which most large carnivores have already been extirpated.

The creation and expansion of wildlife reserves in developing countries offers hope, but carnivores roam too far and existing parks are usually too small to ensure their long-term survival. In 1972, the Nepalese government established a network of parks to preserve tiger habitat, but it did not halt the degradation of critical habitat outside of the preserves, and local extinction resulted (Smith et al. 1998). When Doßana National Park in Spain was expanded, Ferreras et al. (1992) lamented that the extension was a înecessary but still insufficient step forwardø toward preventing the Iberian lynxøs extinction.

The most promising long-term solution to prevent the mass extinction of large carnivores around the world is to protect and expand existing habitats and restore connectivity. Kerley et al. (2002) recommend preventing the construction of roads in the first place, closing unnecessary roads, and restricting access along remaining roads as the most necessary steps to protect Siberian tigers. These measures must be implemented at both landscape and regional levels.

An innovative program initiated by Nepaløs Department of Parks and Wildlife in 1993 allocates 30-50% of park revenues toward communities on the periphery of tiger preserves. These funds will help establish sustainable relationships with the forest through buffer-zone management and community development.

In the new era of globalization, protecting carnivores from the insidious effects of roads will require our diligence and creativity. In addition to adopting the best of available mitigation techniques, we must also strive to cultivate a new culture of tolerance.

--- Adam Switalski is Science Coordinator for Wildlands CPR.

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