Wildlife-Roadway Interactions Wildlife – Roadway Interactions A Report to the Washington State Department of Transportation March 1998 Peter Singleton USDA Forest Service Pacific Northwest Research Station 1133 N. Western Ave. Wenatchee WA 98801 1 Wildlife-Roadway Interactions INTRODUCTION Roads are an important component of the modern landscape. They support the flow of people, goods, and services within towns and across continents. Approximately 4 million miles of roads covering 60,000 square miles of land surface have been constructed in the conterminous United States alone (Forman 1995, Forman and Hersperger 1996). This extensive development has a substantial impact on wildlife habitat quality and connectivity, and poses significant threats to long-term biological diversity. Roads impact wildlife populations and distribution through changes in habitat quantity and quality, direct mortality from vehicle collisions, and division of once large populations into smaller groups at greater risk of extinction and genetic change (Forman 1995; Leedy 1975a, 1975b). Wildlife also has a substantial impact on highway safety. Every year, property damage from animal/vehicle collisions costs more than 1 billion dollars and about 100 people die in these accidents (Conover et al. 1995, Cook and Daggett 1995). A number of excellent reviews on various aspects of this subject are available (Forman 1995, p. 159-172; Foster and Humphrey 1992; Groot Bruinderink and Hazebroek 1996; Jalkotzky et al. 1997; Leedy 1975a, 1975b; Putman 1997). Our primary purpose in this paper is to provide an updated and comprehensive bibliography of the published and unpublished literature on roadway and wildlife interactions and, secondarily, to provide a concise review of wildlife and roadway interactions, discuss techniques to minimize negative impacts, and identify common strategies for improving highway safety regarding animal/vehicle collisions. Particular emphasis will be on techniques to provide animal passage and limit population fragmentation effects. This paper and the associated bibliography (Appendix A) will contribute to the dissemination of the extensive knowledge that has been gathered on this subject. The bibliography also is available from the authors in a computer file format that can be readily imported into bibliography management software to allow keyword and other searches of titles and abstracts. ECOLOGICAL FUNCTIONS AND EFFECTS Roads or road corridors function ecologically as: 1) habitat for the species and their predators and competitors, 2) sources of contaminants and human disturbance, 3) conduits for movement or range expansion, 4) partial or complete filters to animal movement , and 5) mortality agents (Forman 1995). These functions impact wildlife populations and subsequent viability by changing the amount, spatial distribution, and quality of habitats; by changing patterns of interaction between competitors, predators, and prey; and by mortality resulting from vehicle collisions or human access to animals (e.g., shooting, trapping). The combination of these effects can result in reduced wildlife populations and isolation of the remaining animals in smaller groups that are more prone to extinction and genetic change than larger contiguous populations. 2 Wildlife-Roadway Interactions Habitat Substantial amounts of wildlife habitat have been converted into pavement or early- successional vegetation in right-of-ways. Forman and Hersperger (1996) calculated that roads cover approximately 2% of the conterminous United States (about 60,000 square miles). This direct loss of habitat is significant in mountainous areas where roads tend to be concentrated in lower elevation valley bottoms that provide the most productive wildlife habitats (Woods and Munro 1996). Roadsides, however, also can provide unique habitat characteristics associated with early-successional vegetation and edges. Early-successional habitats: Roadside verges are often maintained in early successional vegetative communities for safety concerns and ease in highway maintenance. Early successional roadside communities provide habitat for a variety of animals, particularly small mammals (e.g., Haner et al. 1996, Schwartz et al. 1994, van der Reest 1992), and birds (Hsu and Peterle 1989). Woodchucks in Ontario were found to occur at higher densities in habitats associated with interstate highways and interchanges than in any other habitats (Woodward 1990). Edge habitats: Roads in forested landscapes provide breaks in the forest cover which create conditions suitable for wildlife associated with edge and grassland habitats (Hanowski and Niemi 1995). Road associated edge habitats can increase local species diversity, however, species occupying early successional roadside habitats are often common elsewhere (King et al. 1996). Adams and Geis (1981a, 1981b, 1983, 1984) found grassland and generalist birds and small mammals preferred right-of-way vegetation in a survey of wildlife associated with highways in Virginia, the Carolinas, Illinois, and Oregon. Burke and Sherburne (1982) detected a change in bird species composition due to highway construction through forested habitat in northern Maine (see also Maine Cooperative Wildlife Research Unit 1983). Many species associated with roadside edge habitats are undesirable. Cowbirds are more common along roadside edge habitat than in interior forests (Brittingham and Temple 1983, Camp and Best 1993). Even narrow roads that divide interior forests provide habitat for cowbirds and nest predators and can contribute to substantial negative effects on interior forest songbird populations (Rich et al. 1994, Robinson and Wilcove 1994). In Australia, the exotic, toxic cane toad was found to occur at higher densities along roads and vehicle tracks than in adjacent forested habitats (Seabrook and Dettmann 1996). Foraging opportunities: Early successional roadside habitat can provide foraging opportunities for a variety of species. Black bears in North Carolina exploit berries growing along low volume or closed roads (Beringer et al. 1988). Open areas above roads can provide foraging opportunities for bats, particularly where street lamps attract concentrations of insect prey (Blake et al. 1994, Crome and Richards 1988, Rydell 1992). Ungulates (notably deer) feed on grassy roadsides, especially in forested landscapes or other areas where forage availability may be limited (e.g., Bellis and Graves 1971, Carbaugh et al. 3 Wildlife-Roadway Interactions 1975). Roadside habitats can be attractive for ungulates because cover is often available adjacent to forage and large predator density is usually reduced in the vicinity of open roads (e.g., Mace et al. 1996, Mech et al. 1988). Forage can be more available along roads and railroads in the winter months due to plowing and accelerated snow melt. Rabbits have been documented using roadsides (Kline 1965), and moose using railroad verges (Andersen 1991) during deep snow periods because of superior forage availability. Small and medium sized mammalian predators and raptors may regularly use roadsides because of the availability of small mammals (King et al. 1996) and the ease of foraging along linear strips of edge habitat (Bergin et al. 1997, Marini et al. 1995, Stanley 1991). Kavanagh and Murray (1996) found that a radio-collared masked owl spent 56% of its time within 100 meters of ecotones along roads and fields. Burrowing owls in Colorado tended to locate burrows closer to roads (Plumpton and Lutz 1993). Ferruginous hawks in Montana that nested closer to roads produced more young than other hawks (Zelnak and Rotella 1997). Scavengers often feed on carrion associated with roadways (Conner and Adkisson 1976). Ravens were found to be more common near roads and other linear right-of-ways in the Mojave Desert (Knight and Kawashima 1993, Knight et al. 1995). A variety of snake species also have been documented foraging on road-killed carcasses (Bedford 1991a, 1991b; Hamel 1996). Residual vegetation in developed landscapes: In some developed landscapes, public lands associated with linear right-of-ways can be the only remaining (and best-connected) patches of residual natural vegetation (Bennett 1990, 1991; Daniels 1994). Roadside habitat areas have become central components of conservation planning in many areas including Australia (Cale 1990, Newby and Newby 1987, Stone 1992), South Africa (Dawson 1991), the United Kingdom (Way 1970, 1977), Europe (Darrall 1987, Opdam et al. 1994), and the United States (Adams and Dove 1989, Little 1990, Stevenson 1996, Warner 1992). Residual cover along roadsides can provide habitat for nesting birds, especially in agricultural landscapes (Arnold and Weeldenburg 1990, Berg and Part 1994, David and Warner 1981, Horkel et al. 1981, Kartanas 1996, Kilbride et al. 1992, Leach and Recher 1993, Warner et al. 1992). Camp and Best (1993) documented 35 bird species in roadside habitats compared to 26 species in adjacent rowcrop fields. Warner (1992) found that numbers of nests and species increased with roadside width. Some species of birds are also attracted to ornamental roadside plantings (Dowler and Swanson 1982, Jozsef 1980). During a survey of highway verges and median strips, Munguira and Thomas (1992) documented up to 23 species of butterflies occupying roadside habitat in the United Kingdom. Small mammal use of residual habitats along roads has been documented in Australia (Lindenmayer et al. 1994). 4 Wildlife-Roadway Interactions While residual roadside vegetation plays