The weasel family Mustelidae is the most diverse family of all carnivores ¤ almost 70 species ¤ and is found on every continent except Antarctica and Australia.

Mustelids cover the gamut of habitat types: from terrestrial to aquatic; from underground to treetop; and from fresh ater to salt water. While species like the skunk have been relatively unaffected by increased human presence and development, others like black-footed ferrets and marten have taken a hard hit. The impacts of roads can be broken down into direct (roadkill) and indirect (increased hunting pressure and habitat fragmentation).

Eurasian Badger Meles meles

Eurasian badgers live in clans, which are small social groups with relatively little dispersal, although there is some interchange between clans. Mortality and reproduction within each clan and the exchange of individuals between clans determine the dynamics of the entire metapopulation of badgers (Lankester et al. 1991). To increase badger metapopulation viability, the most effective measures involve a decrease in the adult mortality rate (decreasing local extinction rate) and an increase in the dispersal rate (increasing recolonization rate), both of which are affected by roads.

According to Clarke et al. (1998), îroads have two major impacts on the landscape with respect to badger populations: (1) the imposition of barriers that reduce or prevent dispersal,and (2) the increased mortality caused by road traffic."

Direct Impacts

One of the most likely causes of badger mortality and population decline in Europe is road and railway traffic accidents (Gallagher & Nelson 1979; Wiertz & Vink 1986). In Britain, road traffic is the largest cause of recorded badgers deaths, with an estimated 50,000 killed each year. Road deaths peak from February through April during the main mating season and when territorial behavior (fighting and scent marking) is at a maximum (Davies et al. 1987).

According to Bauduin et al. (1999), forestry and road traffic are the main threats to badgers in the Belgian Ardenne region. A study in Denmark in 1991 found that 10-15% of the total badger population had been killed by traffic (Aaris 1995). In the Netherlands, it was 12% annually ¤ endangering the badger populationøs survival. Despite the construction of more than two hundred wildlife passages in the Netherlands, the number of road killed badgers increased annually by more than 12% during the first half of the 1990øs. However, during the same period the badger population increased, so whether or not passages and fencing reduced the percentage of badgers killed by vehicles is unknown. These passages are also used by mink and weasels, with unknown results (Broekhuizen & Derckx 1996).

Indirect Impacts

Below a certain traffic level threshold, the main impact to badger populations is through direct mortality. However, above this threshold, badgers may not attempt to cross a road at all, thereby creating an effective movement barrier (Clarke et al. 1998). Major roads may therefore reduce dispersal and colonization movements (Lankester et al. 1991). An increase in developed areas and roads results in greater fragmentation of the landscape, and makes potentially suitable areas much less readily available for badger population expansion (Clarke et al. 1998). Lankester et al. (1991) notes that an increase in both the number of roads and the density of traffic is leading to greater isolation of badger populations.

The badger is a rare and threatened species in The Netherlands. A study of badger den use from 1960 to 1980 found that deteriorated badger dens were situated in areas with the highest number of roads by 1980. High numbers of roads in 1980 also coincided with unoccupied dens while low numbers of roads coincided with occupied dens. The number of roads is the only significant variable accounting for changes in den occupation (van der Zee et al. 1992), leading to the conclusion that road density is the most important variable related to decline in badger dens.  

Possible Solutions

Clarke et al. (1998) and Lankester et al. (1991) conclude that road construction should include fences to deter badgers from crossing roads and tunnels and underpasses to increase their survival probability. Lankester recommends reduced speeds, use of road signs, nightly road closures (badgers are nocturnal) and limiting public access to improve badger survival and habitat.Ï

European Otter Lutra lutra

In Britain, the collapse of the otter population in the 1960øs has been attributed to the introduction of organochlorine pesticides. The pesticides contaminated aquatic food chains and left the country with low densities of otters in areas with high road densities (Philcox et al. 1999). Consequently, the number of deaths attributable to road traffic accidents is increasing (Green 1991; Green & Green 1997). The recent expansion of otter populations in Britain and other parts of Europe ¤ combined with developing economies in eastern Europe, and continued road building and increasing traffic flows throughout Europe ¤ has raised concerns about increased mortality of otters on roads (Green & Green 1997). Mason and Macdonald (1996) note that otters are extremely sensitive to water quality and human disturbance. Deterioration of either of these factors by logging or increased access resulting in human use of lakes and rivers will reduce otter numbers (Thompson 1988). Lafontaine (1991) suggests that 5% of Franceøs total otter population may be killed by traffic each year. Kubasch (1992) suggested that 10% of the otter population in Saxony has been lost to road accidents.  

Madsen (1996) examined data from 115 European otters killed by cars during 1980-1995, at the scenes of accidents, and also examined tests of ten fauna passages of various types constructed at existing road bridges. He found that nearly half of the otters were killed at bridges/culverts or dams and concluded that the most dangerous kinds of roads for otters are highways/primary roads and secondary roads wider than 6m with a relatively high traffic density and speed. Madsen suggests appropriately sited fauna passages would effectively reduce the number of traffic-killed otters. Madsen (1990) noted that otters were killed at places without banks under bridges or at dams between two wetlands. His observations indicated that otters are not able to estimate the risk of crossing roads. Road construction projects should lure otters under road systems on stones and banks or use fences to guidethem away from roads.

An extensive study by Philcox et al. (1999) examined otter road casualties in Britain between 1971 and 1996 and found that an increase in the number of road traffic accidents recorded nationally began in about 1983 and has been more rapid than any other known cause of otter mortality. His study indicated that 67.1% of road traffic accidents occurred within 100m of fresh or sea water and that there was no significant difference in number of casualties between culverts, bridges or where no road crossing occurred.

Philcox found that more males than females were killed on roads, probably due to malesø home range expansion, greater dispersal distances, higher energy requirements and less cautious behavior. He determined the majority of deaths coincide with high river flows which implicates the way water is channeled through these crossings as a factor involved in road traffic accidents. Further, there were significantly fewer casualties when a road ran along a stream than when it crossed a stream by culvert or bridge, but roads that are located very close to rivers over long distances also are hazardous to otters. Major roads made a disproportionatelyhigher contribution to road traffic accidents, except for motorways (comparable to our U.S. interstates), where îlarge embankments and greater use of fencing may provide a more effective barrier, and continuous traffic noise may act as a deterrent."

Philcox concluded that high risk zones are those where roads are present within 100m of a watercourse or the coast and that mitigation efforts should focus on these areas to improve the design of river crossings, utilizing wide span bridges which permit retention of the river bank under the bridge.

American Marten Martes americana

Robitaille & Aubry (2000) found that while marten tracks were located near roads, the track density was significantly lower near roads than away from roads. He concluded that marten activity was higher away from roads.

Thompson (1998) determined that access provided by logging roads (including tertiary roads) contributes to increased trapping pressure by reducing the unexploited portions of a trapline. In the area of his study, boreal Ontario, this especially seemed to affect martens. However, many mustelids are hunted and over-hunted for their fur, so increased access to formerly roadless areas could greatly impact trapping of mustelid species.

Conclusion

Roads and road traffic have negatively impacted these three mustelid species. The two European species are faced with such large road and human development densities that perhaps the only practical solution is improved road designs with fences and underpasses. And North American species are facing similar problems in the United States with 6.2 million km of public roads (National Research Council 1997). While Clevenger and Waltho (1999) found that weasels and martens utilized drainage culverts fairly frequently to cross under the Trans Canada Highway, such crossing structures have not yet proven sufficient to minimize the negative impacts of various types of roads on mustelids. Other solutions are needed such as reconnecting fragmented habitat by removing certain roads (for the otter, those that cross or are adjacent to watercourses; for the marten, those roads that expand trapping into previously untrapped areas) and thus increasing the amount of wild land free of human development.

Bibliography

Aaris, S.J. 1995. Road-kills of badgers (Meles meles) in Denmark. Annales Zoologici Fennici 32(1): 31-36.

Bauduin, B., P.P. Pastoret, and B. Brochier. 1999. Evolution of the badger (Meles meles) population density in the Ardenne region (Belgium). Cahiers døEthologie 19(1): 75-82.

Broekhuizen, S. and H. Derckx. 1996. Passages for badgers and their efficacy. Zeitschrift Fuer Jagdwissenschaft 42(2):134-142.

Clarke, G. Philip, P.C.L. White, and S.Harris. 1998. Effects of roads on badger (Meles meles) populations in south-west England. Biological Conservation 86: 117-124.

Clevenger, A.P., and N. Waltho. 1999. Dry drainage culvert use and design considerations for small- and medium-sized mammal movement across a major transportation corridor. Proceedings of the Third International Conference on Wildlife Ecology and Transportation. Evink, Garrett and Zeigler, eds. FL-ER-73-99. Florida Department of Transportation, Tallahassee, Florida: 263-277.

Davies, J.M., T.J. Roper and D.J. Shepherdson. 1987. Seasonal distribution of road kills in the European badger (Meles meles). Journal of Zoology (London) 211(3): 525-529.

Fehlberg, U. 1994. Ecological barrier effects of motorways on mammalian wildlife. Deutsche Tieraerztliche Wochenschrift 101(3): 125-129.

Green, R. 1991. The impact of hunting, poaching and accidents on otter survival and measures to protect individual animals. Proceedings of the V International Otter Colloquium (eds. C. Reuther & R. Rochert). Habitat 6: 171-190. Green, R. & J. Green. 1997. Otter survey of Scotland 1991-94. The Vincent Wildlife Trust, London.

Hodgman, T.P., D.J. Harrison, D.D. Katnik, and K.D. Elowe. 1994. Survival in an intensively trapped marten population in Maine. Journal of Wildlife Management 58(4): 593-600.

Kubasch, H. 1992. Otterschutz in Sachsen. Otterschutz in Deutschland (ed. C. Reuther). Habitat 7: 109-112.

Lafontaine, H. 1992. La loutre et la route. Groupe Mammalogique Breton, DRAE-Bretagne, PNR døArmorique, Societe Francaise pour løEtude et la Protection des Mammiferes.

Lankester, K., R. van Apeldoorn, E. Meelis and J. Verboom. 1991. Management perspectives for populations of the Eurasian badger (Meles meles) in a fragmented landscape. Journal of Applied Ecology 28: 561-573.

Madsen, A.B. 1990. Otters (Lutra lutra) and traffic. Flora Og Fauna 96(2): 39- 46.

Madsen, A.B. 1996. Otter (Lutra lutra) mortality in relation to traffic, and experience with newly established fauna passages at existing road bridges. Lutra 39(2): 76-88.

Mason, C.F. and S.M. Macdonald. 1986. Otters: Ecology and Conservation. Cambridge University Press, Cambridge.

National Research Council. 1997. Toward a Sustainable Future: Addressing the Long-term Effects of Motor Vehicle Transportation on Climate and Ecology. National Academy Press, Washington, D.C.

Philcox, C.K., A.L. Grogan and D.W. MacDonald. 1999. Patterns of otter (Lutra lutra) road mortality in Britain. Journal of Applied Ecology 36: 748-762.

Robitaille, J. F., K. Aubry. 2000. Occurrence and activity of American martens (Martes americana) in relation to roads and other routes. Acta-Theriologica. 45(1): 137-143.

Thompson, I.D. 1988. Habitat needs of furbearers in relation to logging in boreal Ontario. The Forestry Chronicle 64(3): 251261.

van der Zee, F.F., J. Wiertz, C.J.F. Ter Braak, and R.C. van Apeldoorn. 1992. Landscape change as a possible cause of the badger (Meles meles) decline in The Netherlands. Biological Conservation 61: 17-22.