Journal of Environmental Management 88 (2008) 407–415 Are motorway wildlife passages worth building? Vertebrate use of road-crossing structures on a Spanish motorway C. Mata à , I. Herva´s, J. Herranz, F. Sua´rez, J.E. Malo Departamento de Ecologı´a, Facultad de Ciencias, Universidad Auto´noma de Madrid, E-28049 Madrid, Spain Received 21 June 2006; received in revised form 31 January 2007; accepted 10 March 2007 Available online 30 April 2007 Abstract Numerous road and railway construction projects include costly mitigation measures to offset the barrier effect produced on local fauna, despite the scarcity of data on the effectiveness of such mitigation measures. In this study, we evaluate the utility of different types of crossing structures. Vertebrate use of 43 transverse crossing structures along the A-52 motorway (north-western Spain) was studied during spring 2001. Research centered on wildlife passages (9), wildlife-adapted box culverts (7), functional passages (6 overpasses, 7 underpasses) and culverts (14), with marble dust being used to record animal tracks. A total of 424 track-days were recorded, with most of the larger vertebrate groups present in the area being detected. All crossing structure types were used by animals, although the intensity of use varied significantly among them (Kruskal–Wallis test, po0.05); culverts were used less frequently than other structures. Crossing structure type and width were identified as the most important factors in their selection for use. Wildlife passages and adapted culverts allowed crossing by certain species (wild boar, roe deer, Eurasian badger), which do not tend to cross elsewhere. These results highlight the importance of using both mixed-type structures and wildlife passages in reducing the barrier effect of roads. r 2007 Elsevier Ltd. All rights reserved. Keywords: Barrier effect; Habitat fragmentation; Road ecology; Vertebrate; Wildlife crossing structures 1. Introduction Animal population isolation produced by habitat fragmentation constitutes one of the commonest causes of local extinctions (Hunt et al., 1987; Clarke et al., 1998; Lode´, 2000; Fahrig, 2003). Linear infrastructures not only physically destroy habitats but also become barriers, which considerably limit movement and dispersion of terrestrial vertebrates (Oxley et al., 1974; Mader, 1984; Camby and Maizeret, 1987, Walker et al., 2003). As a result, over the last few decades, the inclusion of faunal passages or the modification of existing culverts to serve as crossing structures has frequently been recommended in Environ- mental Impact Assessments and Statements (Beier and Loe, 1992; De Santo and Smith, 1993; van Bohemen, 1998). Wildlife crossing structures aim to re-establish the movement of animals between both sides of a road or railway line, helping to connect the areas affected by the transport corridor (Saunders and Hobbs, 1991; Clergeau, 1993; Rodrı´guez et al., 1996, Putman, 1997). Knowledge of the effectiveness of wildlife crossing structures is still scarce, although increasing quickly. The regular use of different wildlife passage types has been demonstrated for some vertebrate groups (Singer and Doherty, 1985; Foster and Humphrey, 1995; Bekker and Canters, 1997; Gloyne and Clevenger, 2001; Puky and Vogel, 2003; Taylor and Goldingay, 2003; Dodd et al., 2004) but others, like ungulates, are noteworthy for their reluctance to use most crossing structures (Reed, 1981; Vassant et al., 1993; Mata et al., 2005). The key elements for the design of effective mitigation measures are not yet well understood and different solutions may be needed for different faunal groups. The modification of construction projects to adapt culverts for vertebrates or to include wildlife passages imposes costs on new projects. Conse- quently, it is important to evaluate which characteristics of existing crossing structures affect their use by different species, in order to design cost-effective passages for target species in new projects. It is therefore important to ARTICLE IN PRESS www.elsevier.com/locate/jenvman 0301-4797/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2007.03.014 à Corresponding author. Tel./fax: +34 914978011. E-mail address: cristina.mata@uam.es (C. Mata).