Spatial patterns and factors influencing small vertebrate fauna road-kill aggregations

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Abstract

We examined the spatial patterns and factors influencing small terrestrial vertebrate road-kill aggregations in the Bow River Valley, Alberta, Canada. We surveyed roads varying in traffic volume, configuration and adjacent landscape attributes for road-kills between 1997 and 2000. The spatial pattern of road-kills was described using neighbour K statistics. We investigated the importance of road-kills at three taxonomic levels using logistic regression. Mammal and bird road-kill indices were consistently higher on a low volume parkway than on the high-speed, high volume Trans-Canada highway (TCH). Birds were more vulnerable to collisions than mammals on the TCH. Road-kill aggregations were nonrandomly distributed. Parkway road-kills were aggregated on small scales and characterized by low clustering intensities compared to the TCH. Road-kills were less likely to occur on raised sections of road. Road-kills tended to occur close to vegetative cover and far from wildlife passages or culverts. Our findings reveal how two distinct road types can have different effects in terms of vertebrate mortality and their spatial pattern. We recommend a series of mitigation measures for existing roads or future road planning projects.

Introduction

Studies of vehicle-caused wildlife mortality have covered a broad taxonomical spectrum, yet collisions with deer and other large mammals such as moose Alces alces and elk Cervus elaphus have stimulated much of the research (Reed et al., 1979, Woods, 1990, Lavsund & Sandegren, 1991). Research results have largely been descriptive and anecdotal reporting on surveys or counts of animals killed by vehicles, age and sex characteristics of road-kills, and seasonal patterns. Although counts of dead animals can be useful for evaluating the magnitude of road-kills, they are inadequate for understanding the relationship between roads and wildlife.

The importance of habitat and road variables influencing bird collisions with vehicles has long been recognized (Barnes, 1936, Finnis, 1960). Previous analyses of factors explaining road-kills have focused primarily on large mammals (Bellis & Graves, 1971, Bashore et al., 1985, Groot Bruinderink & Hazebroek, 1996), whereas few formal studies have investigated the role of road and landscape variables influencing small fauna road-kills (Oxley et al., 1974, Fahrig et al., 1995, Massemin & Zorn, 1998, Philcox et al., 1999).

Research on large mammal road-kill aggregations has demonstrated that they do not occur randomly but are spatially clustered (Puglisi et al., 1974, Child, 1998, Hubbard et al., 2000, Clevenger et al., 2001a, Joyce & Mahoney, 2001). Wildlife tends to be linked to specific habitats and adjacent land use types. Thus, landscape spatial patterns would be expected to play an important role in determining road-kill locations and rates (Forman and Alexander, 1998). Explanatory factors of wildlife road-kills vary widely between species and taxa. To understand the importance of such factors and processes, it is first necessary to be able to measure and describe the spatial pattern of road-kill aggregations.

Where vehicle speed and/or road density are high, road traffic has been shown to have a severe local effect on animal road-kills (Rosen & Lowe, 1994, Drews, 1995, Jones, 2000). Increased traffic flows in Banff National Park (BNP) have raised concerns about increased road-kills of wildlife (Banff-Bow Valley Study, 1996). One strategic goal of the BNP management plan was to reduce wildlife road-kills on the Trans-Canada highway (TCH) and other roads in and adjacent to the park (Parks Canada, 1997). The lethal impacts of park roads on large mammals has been investigated (Woods, 1990, Clevenger et al., 2001a), yet virtually nothing is known about road-kills of smaller vertebrate fauna. To support efforts to mitigate road impacts at all levels of species organization, management needs to be able to identify where particular individuals, species, taxa, and vertebrate communities are susceptible to high road-kill rates along roads.

We quantified road-kill occurrence among small terrestrial vertebrates in the Bow River Valley. We identified seasonal and geographic patterns of road-kills. We tested whether road-kills occurred randomly and, in the event they were spatially clustered, whether road-kill aggregation characteristics were taxa-specific. Finally, we evaluated the relative importance of factors associated with road-kills of small terrestrial vertebrates on a variety of roads varying in vehicle traffic, road configuration and adjacent landscape attributes.

Section snippets

Study area

This study took place in the Central Canadian Rocky Mountains in western Alberta approximately 100 km west of Calgary (Fig. 1). The area encompasses the Bow River watershed comprising mountain landscapes in BNP and adjacent Alberta Provincial lands in Kananaskis Country. Topography is mountainous, elevations range from 1300 to over 3400 m, and valley floor width varies from 2 to 5 km.

We selected two roads within our study area, both had varying traffic volumes, vehicle speeds, road

Species composition and temporal pattern of road-kills

Our surveys sampled a total of 65,253 km of roads. Of this distance, 14,659 km were surveyed on the Parkway and 50,594 km on the TCH. Sampling took place on 554 days; 226 (40%) of those days no road-kills were found. The average number of sampling days without recorded road-kills was highest in May and October and lowest in July and August.

A total of 677 animals (56 identified species) were collected at 669 sites. These included 313 mammals (18 species), 316 birds (36 species) and 48 amphibians

Species composition and temporal pattern of road-kills

Compared to the sampling effort undertaken to quantify road-kill occurrence in our study area kill rates were remarkably low. We surveyed 65,000 km of road during 550 days and documented 674 road-killed animals. Previous studies have reported greater numbers of road-kills while sampling shorter road sections during shorter periods (Fahrig et al., 1995, Ashley & Robinson, 1996, Kline & Swann, 1998). The low kill rates we report may be explained by climatic conditions in our study area,

Acknowledgements

This study was funded by Parks Canada and Public Works and Government Services Canada (contract C8160-8-0010). M. Brumfit, S. McNalley, E. Zidek, W. Hollett, M. Edwards and L. Holmstol assisted with field work. D. Zell provided GIS assistance and C. Hourigan helped with library services. The paper was improved by the critical comments of P. Singleton, R.G. Wright and an anonymous reviewer. We thank T. McGuire for securing funds for the research and D. Dalman, T. Hurd, and C. White and for their

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