Michael J. Starr
and
Students of the Department of Geography
Southern Illinois University Edwardsville
Edwardsville, IL 62026-1459

1. BACKGROUND

During the early part of the 19th century, there was already an extensive road network east of the Rocky Mountains, however, less than 4% of the nearly 2 million miles of roads were paved (Forman et al, 2003). After World War II, the economy was improving which led to increased affluence, more car purchases and more miles being driven. In 1956, the Federal Interstate Highway Act was passed, the first of many such acts giving monetary aid for the construction and improvement of the nation's roads and highways. Suburbs on the outskirts of cities began to grow and commuting became more common. By 1980, people in the suburbs outnumbered those in the cities, and the number of cars owned had increased to 1 car for every 2 people with each person driving an average of 7,000 miles per year (Havlick, 2002; Mitchell, 2001).

Today there are nearly 4 million miles of road, of which more than 60% are paved and at least 2 lanes wide. The number of cars in the U.S. exceeds 200 million, with each person driving over 10,000 miles per year on average. While roads of all types have been shown to fragment natural habitat, in part by creating isolating barriers to species dispersal (Adams & Geis, 1983; Mader 1984; Oxley et al, 1974), some individual animals will occasionally attempt to cross these roads, sometimes with dire consequences when they are hit and killed by a passing vehicle.

Such animal mortalities have undoubtedly been occurring since the earliest roads were built. Perhaps the earliest well-documented example of a road-kill is a turtle that was crushed by a wagon wheel in North Dakota in 1897 (Knutson, 1987). Later, during the 1930's and 1940's a few rigorous studies were done in the Midwest, and these found more than 7000 road-kills, representing more than 100 species (Knutson, 1987; McClure, 1951). In addition, while it is undoubtedly true that the number of road-killed animals has been increasing through the years in conjunction with increasing road mileage, vehicle travel and driving speeds, until the last decade, very few scientific studies had been conducted to assess this assumption (Clevenger et al, 2001; Forman et al, 2003).

Further, there is still no systematic record keeping regarding the number of animals killed on the nation's roads. However, since most states now require police reports when vehicles sustain sufficient damage in an accident, the total number of large animal/vehicle collisions can be pieced together by collecting these data. From these data, it has been conservatively estimated that 1 million deer alone are killed each year on the nation's roads (Forman et al, 2003). While the data on small animals is much less comprehensive, a few researchers estimate that at least one million small mammals are killed on the nations roads each year (Forman et al, 2003). A number of studies suggest that birds are generally the most frequent road causality (Clevenger et al, 2001; Knutson, 1987; Mitchell, 2001), while reptiles and amphibians as a group are the most underrepresented in road-kill surveys (Forman et al, 2003; Trombulak & Frissell, 2000). When all these data are combined, some researchers now suggest that animal deaths by road-kill may exceed the total number of deaths by all other causes combined (Forman et al, 2003).

Since more research needs to be done on the effects of roads on small vertebrate animals, we have begun a program utilizing college students to survey rural roads and state highways in Madison County, Illinois. Our initial goal is to quantify the scope of the road-kill problem in our area and to identify both the most vulnerable taxa along with some of the key risk factors.

2. STUDY AREA AND METHODOLOGY

The study area is located in Madison County, Illinois, which lies just east of St. Louis, Missouri. This region was initially settled in the late 1700's and even today retains a predominantly rural environment, with farmlands surrounding the small, but slowly growing cities and towns. In the early 1960's, a new interstate bridge across the Mississippi River led to a 12% population growth that was part of the general urban sprawl in the St Louis area. As a result, Madison County now contains many new sub-divisions with homeowners commuting back to the city to work. This increasing population and vehicular traffic make this area a great place to study the impact of road use on small vertebrate animals.

Three survey routes were established within easy driving distance of our campus. Each route was a total of 20 km long; this included 10 km of narrow paved but un-striped roads through rural areas and 10 km of 2-lane state highways. Land use along the rural survey sections was primarily agricultural (with corn, soy beans and winter wheat the major crops), with some pastures for livestock grazing and homes with lawns and landscaping. The state highways passed through similar agricultural areas and pastures, but also included more suburban development from housing to local retail and food establishments. Traffic volume (counted during the surveys) and speed (estimated) were both generally much higher on these roads.

FIGURE 1
ROAD-KILL ROUTES

Students from my lab courses were trained in both the survey methods and in the identification of road-killed animals. For this study, the focus is on small vertebrates, defined as those weighing less than about 35 lbs (16 kg), or about the size of a large raccoon. However, larger vertebrates were noted if observed. The survey routes were driven at least once per week, generally after the morning work traffic, with at least 2 student observers per vehicle. On the rural portions, the vehicle was driven about 15 mph, while on the state highways, the vehicle was driven about 30 mph (or about 20 mph below the average speed of traffic for safety reasons). When a road-killed animal was found, the individual was identified in terms of species, gender and age class if possible. In addition, the general location of the road-kill along the survey route was recorded along with a general description of the road surface, edge, and the surrounding area.

3. SOME INITIAL RESULTS

During the last year, we were able to conduct over 40 surveys along each survey route, resulting in a total of more than 800 km of rural roads and 800 km of state highways being surveyed. The amount of traffic along the rural routes ranged between 10-20 vehicles per hour (200/day), traveling at speeds estimated to be between 65-80 kph (40-50 mph). Traffic on the highways was much greater, ranging from 2-6/minute or ranging between 100-350/hour (4000-8000/day), and much faster, with estimated speeds of 100 kph or more (60 mph).

During this survey period, over 300 individual road-kills were found and recorded (see Figure 1). Of this total, over 58% were mammals, with about 25% of those being opossums (Didelphis virginiana). Birds accounted for about 32% of the total number of road-kills while the herptiles (amphibians and reptiles) made up about 10% of the total. Other apparent patterns include the number of road-kills on the highways being nearly double that of rural roads (presumably a result of more vehicle traffic and speed) and more road kills found in spring and early summer than any other season. In addition, the spring-early summer increase was largely due to increased bird and herptile road-kills, while mammals made up more than 70% of the total in fall. Overall, the average number of road-kill for highways was about 0.29 animals/km, while the average for rural roads was about 0.13 animals/km. While these data are still preliminary, they are within the low end of the range for the average numbers of road-kill/km found in other similar studies (Clevenger et al, 2003; McClure 1951), and therefore support at least the most conservative estimates of road kill numbers. However, in spite of some on-going adjustments, both our bird and herptile totals appear to be lower than is commonly found in other similar studies. Therefore, in order to further our work on this topic in an attempt to clarify some of these issues, we continue to recruit new and interested students to conduct research for their senior assignments and/or master's theses.

FIGURE 2
OVERVIEW OF ROAD-KILL DATA

4. SELECTED REFERENCES

Adams, L.W. and A.D. Geis. 1983. Effects of Roads on Small Mammals. Journal of Applied Ecology 20: 403-415.

Clevenger, A.P., B. Chruszcz, & K.E. Gunson. Spatial Patterns and Factors Influencing Small Vertebrate Fauna Road-Kill Aggregations. Biological Conservation 109: 15-26.

Forman, R.T.T., et al. 2003 Road Ecology, Science and Solutions. Washington: Island Press.

Havlick, D.G. 2002. No Place Distant. Washington: Island Press.

Knutson, R.M. 1987. Flattened Fauna. Berkeley, CA: Ten Speed Press.

Mader, H.J. 1984. Animal Habitat Isolation by Roads and Agricultural Fields. Biological Conservation 29: 81-96.

McClure, H.E. 1951. An Analysis of Animal Victims on Nebraska's Highways. Journal of Wildlife Management, 15: 410-420.

Mitchell, J.G. 2001. Urban Sprawl, the American Dream. National Geographic, July 2001: 48-68.

Oxley, D.J., M.B. Fenton and G.R. Carmody. 1974. The Effects of Roads on the Populations of Small Mammals. Journal of Applied Ecology 11: 51-59.

Trombulak, S.C., and C.A. Frissell. 2000. Review of Ecological Effects of Roads on Terrestrial and Aquatic Communities. Conservation Biology 14(1): 18-30.

For more information, or to become involved in this project, contact Dr. Starr.

URL: http://www.siue.edu/GEOGRAPHY/RoadKill.htm
Published by: SIUE Department of Geography
Last update: February 2, 2006 by gacheso@siue.edu