ORIGINAL ARTICLE Fernando Ascensa˜o Æ Anto´nio Mira Factors affecting culvert use by vertebrates along two stretches of road in southern Portugal Received: 4 October 2005 / Accepted: 31 March 2006 / Published online: 21 July 2006 Ó The Ecological Society of Japan 2006 Abstract A major target for environmental managers when trying to minimise the road-barrier effect on wildlife is to improve permeability to animal move- ments. Previous studies have demonstrated that drain- age culverts are used by vertebrates, although knowledge of the main influencing factors remains limited. The use of 34 culverts from two roads in southern Portugal, differing in traffic volume, vehicle speeds and configu- ration, was evaluated by the analysis of terrestrial ver- tebrate footprint data (408 passage-operative days). Culvert crossings were related to various explanatory variables by means of canonical ordination techniques. We recorded 901 complete crossings, corresponding to an average of 2.2 crossings/culvert/operative day. Thir- teen taxa were detected, all in more than one passage. Animal species included reptiles, small mammals, lag- omorphs, carnivores and domestic dogs and cats. Our results suggest that fencing might have a funnelling ef- fect, directing larger animals toward culverts. Also, vegetation covering culvert entrances seems to have a positive effect, particularly on genets; longer passages with entrances far from the pavement were, apparently, avoided by smaller animals; a lower number of crossings was detected on passages with detritus pits; the closest passages to urban areas are more often used by domestic species; forest-living species favour passages with low, open land cover nearby; and smaller species, like lag- omorphs and small mammals, appear to use more cul- verts near the pavement, which probably reflects the importance of road verges as refuges for these species. Although not used by all species present in the study area, constructing numerous passages of different sizes without detritus pits and which are distributed along roads might be an important step in mitigating road fragmentation effects on animal populations. Keywords Road ecology Æ Culvert use Æ Conservation Æ Canonical ordination Æ Vertebrates Introduction Civilisation has always interacted with the landscape, exploiting natural resources and settling human com- munities throughout the world. This has promoted the fragmentation of the landscape on a vast scale. Land- scape fragmentation is now recognised as one of the major threats to the conservation of biodiversity (Saunders et al. 1991; Forman 1995). One major human agent of habitat fragmentation is the ever-increasing network of roads worldwide (For- man et al. 2002), which can be harmful to various faunal groups, including invertebrates (e.g. Haskell 2001), amphibians (e.g. Carr and Fahrig 2001), reptiles (e.g. Gibbs and Shriver 2002), birds (e.g. Kuitunen et al. 1998) and mammals (e.g. Philcox et al. 1999). Roads and traffic can act as barriers which interfere with animal movement and reduce population connectivity, dimin- ishing gene flow and disrupting sink and source popu- lation dynamics, thereby, promoting inbreeding and loss of genetic diversity (Ferreras 2001). The resultant iso- lation might increase the extinction risk of local popu- lations, due to stochastic effects (van der Zande et al. 1980; Saunders et al. 1991; Fahrig and Merrian 1994; Cooper and Walters 2002). Roads also promote high animal–vehicle collision rates (e.g. Hodson 1960; Oxley et al. 1974; Ferreras et al. 1992; Philcox et al. 1999; Gibbs and Shriver 2002; Taylor and Goldingay 2004), one of humankind’s most visible road-related sources of impact upon wildlife. Previous research has provided clear evidence that a wide range of species may be affected by this threat, which can lead to local population extinction (Fahrig et al. 1995; Jones 2000). Additionally, roads may affect animal behaviour, resulting in complete reluctance to cross a road, leading to a barrier effect (Mader 1984; Goosem 2001). For a more detailed review of road ef- F. Ascensa˜o (&) Æ A. Mira Unidade de Biologia da Conservac¸a˜o, Departamento de Biologia, Universidade de E ´ vora, Nu´cleo da Mitra, Apartado 94, 7002-554 E ´ vora, Portugal E-mail: fernandoascensao@yahoo.com Ecol Res (2007) 22: 57–66 DOI 10.1007/s11284-006-0004-1