Transportation Research Part D 14 (2009) 447–452

Contents lists available at ScienceDirect

Transportation Research Part D

journal homepage: www.elsevier .com/ locate/ t rd

Seasonal changes in wildlife use of motorway crossing structuresand their implication for monitoring programmes

Cristina Mata *, Israel Hervás, Jesús Herranz, Juan E. Malo, Francisco SuárezDpto. de Ecología, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049-Madrid, Spain

a r t i c l e i n f o

Keywords:Habitat fragmentationRoad ecologyVertebratesWildlife passages

1361-9209/$ - see front matter � 2009 Elsevier Ltddoi:10.1016/j.trd.2009.05.001

* Corresponding author. Tel.: +34 914978011.E-mail address: cristina.mata@uam.es (C. Mata).

a b s t r a c t

Multiple factors determine the use and effectiveness of wildlife passages and crossingsinstalled in new roads as mitigation measures against the barrier effect. It is unknownwhether factors such as seasonality determine the use of these structures. This analysesthe seasonality of structure used by vertebrates. Forty-eight transverse structures crossingthe A-52 motorway in north-western Spain are studied during the summer and winter of2002–03. The use of structures by terrestrial vertebrates was monitored by tracks left inmarble dust and photographic systems, and comparisons carried out by means of general-ized lineal methods for count data. Structural factors mostly determined the differentialuse of passage types by species but seasonal changes were detected both in the intensityof use and in passage selection by some species.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

The continuing expansion of road networks splits the landscape in fragments, generating multiple impacts on the faunaand currently constituting one of the main threats for several vertebrate species (Trombulak and Frissell, 2000). Road build-ing produces multiple effects, among which loss and degradation of the habitat, an increase in mortality due to road kills andreduction in landscape connectivity stand out (Forman et al., 2003). Moreover, in addition to the physical barrier the infra-structure produces, a change in the behaviour in the form of an ethological barrier is detected in some species (McGregoret al., 2008).

In consequence, mitigation measures such as specific fauna passages and modifications of transverse structures have beenincorporated in new infrastructures to reduce the barrier effect. With them a certain degree of connectivity between habitatsmay be kept and genetic exchange between animal populations on both sides is possible (Haddad et al., 2000). Followinginternational regulations and guidelines for Environmental Impact Assessment (Iuell et al., 2003), in some countries, suchas Spain, compulsory monitoring programmes are being established for new infrastructures to evaluate effectiveness of suchmitigation measures.

Animal use of fauna passages and their effectiveness for mitigation are determined by multiple factors but knowledgeabout them is still scarce. Until now, studies have focused on how structure use is related to the characteristics of their loca-tion and size (Mata et al., 2005). Although potentially important in terms of animal protection, seasonality has been littlestudied: animals may differentially use structures along their life-cycle it (e.g. dispersing juveniles vs. adults in search ofmates), under contrasting meteorological conditions or as response to seasonal variations in traffic volume (Gagnon et al.,2007a). Such changes could point to different species’ needs along the year and they would force mitigation measures as wellas monitoring programmes to be designed accordingly.

. All rights reserved.

448 C. Mata et al. / Transportation Research Part D 14 (2009) 447–452

Within this framework, seasonal use by vertebrates of motorway crossing structures is analysed in this study with a focuson species changes in either their intensity of use or their selection among passage types. Our working hypotheses are thatseasonal changes in animal use of transverse structures to the motorway take place due to variations in activity patterns, butselection of passage type by animal species is constant over the year. Changes in either of them should be addressed whendesigning monitoring protocols for barrier effect mitigation measures (e.g. to decide about monitoring frequency andseason).

2. Methods

The study was undertaken along a 55 km stretch of the A-52 motorway between Santa Marta de Tera and Palacios de San-abria (Zamora province, NW Spain, Fig. 1). This is a four-lane motorway open to traffic since 1998 and it is fenced periph-erally along its length.

The stretch under study has 120 transverse structures (wlidlife- and non-wildlife-engineered passages), with an averagedistance between them of 457 m. The landscape is dominated by forest fragments, scrubs and open areas with a slight in-crease in humidity from east to west that leads to a progressive substitution of holm oak (Quercus rotundifolia) by Pyreneanoak (Quercus pyrenaica) among trees. Broom (Cytisus multiflorus, C. scoparius) scrubs are scattered along the whole stretchaccompained by gum cistus (Cistus ladanifer) in the first 30 km and lower scrub formations (Genista tridentata, Halimium ocy-moides, H. lasianthum) in the rest. Valley botoms are occupied by cereal crops, Agrostis castellana pastures and wet meadows.

Fieldwork took place during two different periods: between June and August 2002 (17.9 �C average temperature and18.6 mm mean monthly rainfall) and from February to the end of March 2003 (7.3 �C average temperature and 40.9 mmmean monthly rainfall). For simplicity, these periods will be referred as ‘summer’ and ‘winter’ hereafter. In addition toweather, traffic volume changes seasonally. During winter this motorway supported an average traffic volume of �6000vehicles/day whereas along summer months it supported an average of �12,000 vehicles/day (Statistics of Spanish Ministryof Public Works, Fomento, 2002, 2003).

Forty-eight crossing structures were selected for study, including all those specifically designed for wildlife as well as asample of each of all the remaining types. Transverse structures were grouped according to functional and structural char-acteristics into the six types shown in Table 1. Crossing by vertebrates was monitored in all structures during the above men-tioned summer and winter periods.

Each crossing structure was visited daily until 10 days of valid records per season were obtained. Invalid days were de-fined as those when weather conditions precluded a neat identification of tracks or when photographic systems failed. Ten-day survey periods have been recommended for maximizing the information-to-cost ratio in monitoring wildlife passages,allowing the detection of more than 60% species using each transverse structure (Malo et al., 2005).

Two monitoring systems were used: track beds and a photographic system designed specifically for this study. Marbledust was used as the substrate for registering track impressions (Yanes et al., 1995). Control strips were laid perpendicular

Fig. 1. Location of the A-52 motorway stretch under study in the Iberian Peninsula.

Table 1Characteristics of the monitored crossing structures: type, number, control method, dimensions and function.

N Control system Dimensions (m) Main function

Analysis of tracks Photographic system Both Width Height Length

Circular culverts 17 7 2 8 Ø1.80 35–63 DrainageAdapted culverts 4 – 4 – 2 2 37–50a Drainage, adapted for wildlifeUnderpasses 11 3 4 4 4–9 3–6 32–44 Rural tracks and livestock pathsWildlife underpasses 5 – – 5 14–20 4–8 30–33b Wildlife, closed to vehiclesOverpasses 9 3 3 3 7–8 – 58–65 Rural tracksWildlife overpasses 2 – 2 – 16 – 60 Wildlife, closed to vehicles

a One case of 150 m.b One case of 96 m.

C. Mata et al. / Transportation Research Part D 14 (2009) 447–452 449

to and half-way along the main axis of the crossing structure. Strips were 1 m wide and between 3 and 10 mm thick, varyingin function with the roughness of the surface on which they were laid.

Track identification was made following Blanco (1998), Bang and Dahlstrom (2001) For numerous tracks, identification tospecies level was not feasible due to the presence of more than one species with very similar tracks. As a result, specieswhich could be erroneously recorded were placed into faunal groups (Table 2). However, the photographic recording systemallowed the specific identification of some groups. It consisted of three elements: infrared beam detector, digital camera anda transmitter to connect the detector to the camera. The infrared detector was equipped with active sensors, an infraredemitter and two receptors, located just above ground level to detect crossing of even the smallest vertebrates.

Out of 48 passages monitored, marble dust was used in 13, camera traps were installed in 15 and both systems were usedsimultaneously in the remaining 20 (Table 1). The results obtained from both systems are comparable, provided that the fau-nal groups are maintained when using camera traps (Mata et al., 2006), although specific identification is possible using thislatter method.

The unit of measurement for analysis was the number of days that a species or faunal group was detected using a crossingstructure in a given season, so minimizing problems of pseudoreplication due to possible multiple counts of a particular spe-cies on a single passage on a given day. Global analyses comprise all 48 structures and they have been complemented withanalyses based on data obtained from 35 passages with camera traps. Data have been analysed by means of repeated mea-sures Poisson-GLZ Models for count measures with season as the repeated measure and passage type as factor (Faraway,2005). Analyses were carried out with R-package for species with more than five presences. Post-hoc comparisons wereafterwards conducted for species with a significative differential use among passage types. Such comparisons were carriedout with Mann–Whitney U tests followed by Bonferroni sequential correction of p values (Rice, 1989).

The photographic system allowed the discrimination within small mustelids (Mustela nivalis and M. erminea), cats (Felissilvestris and Felis catus), canids (Canis lupus and Canis familiaris) and lagomorphs (Oryctolagus cuniculus and Lepus granaten-sis).Thus, data for these species obtained from passages with cameras were also subjected to the analytical procedures.

Neither human disturbance nor vegetation were included in the analyses, given that both factors do not significantly af-fect the patterns of crossing structure use by vertebrates in the study area (Mata et al., 2005).

3. Results

In the 48 crossing structures 1052 track-days were recorded over 960 passage-days. A total of 19 different species/groupswere recorded, with small mammals (mice, voles and shrews) being the most frequent group during both study periods(Table 2). Red fox (Vulpes vulpes) and lagomorphs were also recorded with high frequency, followed by canids and badger(Meles meles). The remaining species or groups showed much lower frequencies of use. Considered together (Fig. 2), use levelswere slightly higher in summer than in winter1 but differences were globally non-significant. However, significative differencesof use were detected among passage types, with wildlife underpasses being the most used structures and adapted culverts theleast. Seasonal differences among passage types were also found due to a remarkable decrease in use of wildlife overpasses insummer (Fig. 2).

Five species with less than six records were not included in further analysis (garden dormouse – Elyomis quercinus; redsquirrel – Sciurus vulgaris; large mustelids – Martes spp.; wild boar – Sus scrofa; and stoat – Mustela erminea).

Seasonal differences in road crossing have been detected for six species/species groups in the whole dataset (Table 3).Water voles (Arvicola spp.) was the only taxon using crossing structures of the motorway significantly more often in winter.On the contrary, anurans, lacertids, ophidians, hedgehog (Erinaceus europaeus) and lagomorphs were more frequently foundcrossing the motorway in summer. In fact, reptiles and hedgehog were only detected in summer. Data from the photographicsystem showed that seasonal differences in lagomorphs were due to changes in rabbits (O. cuniculus) but not in hares(L. granatensis).

1 The mean number of track-days by crossing structure plus or minus a standard deviation was 1.21 ± 0.10 in summer and 0.98 ± 0.09 in winter.

Table 2Average number of day-detections per crossing structure for species and species groups detected throughout the monitoring period in each sampling season.

Circular culvertn = 17

Adapted culvertn = 4

Underpassesn = 11

Wildlife–underpasses n = 5

Overpasses n = 9 Wildlifeoverpasses n = 2

Total n = 48

Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter

SpeciesErinaceus

europaeus0.12 – – – 0.45 – – – – – – – 0.15 –

Eliomysquercinus

0.12 – – – – – – – – – – – 0.04 –

Sciurusvulgaris

– – 0.25 – – – – – – – – – 0.02 –

Meles meles 0.29 0.59 0.75 0.5 1.55 1.36 1.8 2.6 – – – 1 0.71 0.88Genetta

genetta0.06 0.12 – – – – 1 0.4 – – – – 0.13 0.08

Vulpes vulpes 0.94 0.82 0.25 – 3.18 2.27 4.8 3.4 1 0.56 – 5 1.77 1.48Cervus

elaphus– – – – 0.18 – – – – – – 2.5 0.04 0.10

Sus scrofa – – – – – – – 0.40 – – – – – 0.04

Groups of speciesa

Anurans 0.18 – 0.25 – 0.27 0.09 0.2 – – – – – 0.17 0.02Lacertids 1.88 – – – 0.09 – 1 – – – – – 0.79 –Ophidians 0.18 – – – 0.09 – – – 0.22 – – – 0.13 –Small

mammals6.53 6.18 3 – 2.09 1.18 1.2 2.6 3.44 2.89 – – 3.81 3.27

Rats 0.47 0.65 – – 0.18 – 0.2 – – – – – 0.23 0.23Water voles 0.18 0.65 1 2.25 – 0.45 – – – – – – 0.15 0.52Small

mustelids1.24 1.12 0.25 – – 0.09 – – – – – – 0.46 0.42

Largemustelids

– 0.06 – – – 0.18 – – – – – – – 0.06

Cats 0.12 0.06 1.25 – 0.36 0.36 0.8 – 0.67 0.78 – – 0.44 0.25Canids 0.71 0.24 0.25 – 1.55 1.73 2.4 2 1.11 1.89 1 4 1.13 1.21Lagomorphs 0.41 0.24 – – 2.73 2.64 3.6 0.6 3.78 1.89 2.5 3.5 1.96 1.25

a Anurans (all frogs and toads), lacertids (Lacerta spp., Psammodromus spp. and Podarcis spp.), ophidians (all snakes and legless lacertids), small mammals(mice, voles and shrews), water voles (Arvicola sapidus and A. terrestris), rats (Rattus rattus and R. norvegicus), lagomorphs (Oryctolagus cuniculus and Lepusgranatensis), small mustelids (Mustela nivalis and M. erminea), large mustelids (Martes foina and M. martes), cats (Felis catus and F. silvestris) and canids (Canisfamiliaris and C. lupus).

450 C. Mata et al. / Transportation Research Part D 14 (2009) 447–452

A year-round significant differential use of passage types has been found in eight cases (Table 3). Circular culverts werepreferentially used by lacertids, small mammals and small mustelids, and this last group was also more frequent in adaptedculverts than in other passage types. Underpasses and wildlife underpasses were selected by badger, red fox and canids, andcanids also showed a preferential use of overpasses. Among canids, the photographic system only showed a differential useof passage types by wolves (C. lupus), which only used overpasses and wildlife overpasses. Lagomorphs were more frequentlydetected in underpasses, wildlife underpasses and overpasses, and photographic data showed differences only for hares. Fi-nally, red deer (Cervus elaphus) showed a marginally significant association with wildlife overpasses.

Seasonal changes in passage type selection have been detected in four species/species groups (the interaction passagetype by season term in Table 3). Thus small mammals preferentially used adapted culverts and underpasses in summer,but they appeared more frequently in wildlife underpasses during winter. Lagomorph preferences changed from wildlifeunderpasses in summer to wildlife overpasses in winter. Data from photographic systems showed significative differencesonly in the seasonal selection of crossing structures by rabbit. A parallel trend to use wildlife overpasses in winter was de-tected in red fox and canids, and canids also prefered overpasses only in winter. Red fox and canids showed no preferentialuse of any passage type restricted to summer. Among canids, photographic recording showed significative differences in thepassage type by season term only for dogs.

4. Discussion

Results show a marked seasonality in the intensity of use by vertebrates of transverse structures to the road and smallerchanges in passage type selection, both findings having relevant implications for the design of monitoring programmes innew roads. Moreover, the current study represents the first in-depth treatment of seasonal patterns of selection in theuse of crossing structures that considers a wide range of vertebrate species and includes a large sample of different crossingstructure types, both wildlife-specific and of other types.

The main seasonal variation found is a marked variation in the intensity of passage use, with a heavier use of them insummer. Following expectations heavier summer use is conditioned by the presence of species whose activity is strongly

CC AC UP WUP OP WOP0

4

8

12

16

20

24

Num

ber o

f cro

ssin

gs in

10

days

Fig. 2. Recorded use by vertebrates of motorway crossing structures by passage type during summer (empty bars) and winter (striped bars). Note: CC:circular culverts, AC: adapted culverts, U: underpasses; WU, wildlife underpasses, O: overpasses, and WOP: wildlife overpasses.

Table 3Results by species of the Poisson GLZ tests for changes in crossing structure use related to type of crossings structure and season.

Differential use by passage type (df. 5) Differential frequency by season (df. 1) Interaction passage type by season (df. 5)

v2 p Preference v2 p Preference v2 p

Anurans 3.49 0.625 6.20 0.013 Summer 1.78 0.879Lacertids 28.31 <0.001 CC 52.68 <0.001 Summer <0.01 >0.999Ophidians 2.43 0.787 8.32 0.004 Summer <0.01 >0.999Small mammals 37.44 <0.001 CC 1.99 0.159 20.71 <0.001Rats 1.54 0.909 <0.01 >0.999 4.66 0.459Water voles 1.62 0.899 10.74 0.001 Winter 3.02 0.697Hedgehog 0.88 0.972 9.70 0.002 Summer <0.01 >0.999Small mustelids 13.80 0.017 CC, AC 0.09 0.760 2.78 0.734Badger 17.74 0.003 WUP, UP 0.84 0.358 4.46 0.456Genet 3.46 0.629 0.40 0.526 1.26 0.939Cats 6.73 0.242 2.48 0.115 10.40 0.065Red fox 25.92 <0.001 WUP, UP 1.26 0.262 18.16 0.003Canids 20.43 0.001 OP, UP, WUP 0.14 0.706 11.41 0.044Lagomorphs 33.23 <0.001 OP,UP, WOP 7.57 0.006 Summer 11.27 0.046Red deer 9.57 0.088 WOP 1.33 0.249 8.38 0.137

Notes: Significative differences are marked in bold followed by the detected preference. Passage types: circular culverts (CC), adapted culverts (AC),underpasses (UP), wildlife underpasses (WUP), overpasses (OP) and wildlife overpasses (WOP).

C. Mata et al. / Transportation Research Part D 14 (2009) 447–452 451

restricted by weather, such as hibernating ones (hedgehog) or poiquiloterms (amphibians, reptiles). This variation also mir-rors changes in the activity of most species and in the abundance of some species due to their population dynamics, the caseof rabbit outstanding among them (Blanco, 1998).

The only exception to peak use in summer corresponds to water voles, as they appear in road passages (under the road inall cases) mainly in winter. The fact that drainage structures in the area hold water constantly only in winter probably leadssome water voles to include them seasonally in their ranging area (Fedriani et al., 2002). Thus, preferential use of structuresin winter seems in our case to be linked to habitat changes at a small scale, but in other areas it may be related to large scaledisplacements of vertebrates as found for cougars crossing the Transcanadian Highway (Gloyne and Clevenger, 2001).

Contrary to expectation, some differential use of passage types between seasons has been detected at both the aggregatedand the species-by-species levels. Thus, wildlife overpasses were less used in summer than in winter as opposite to the in-crease detected in the rest of passage types (Yanes et al., 1995; Rodríguez et al., 1996). At the species level, selectivity amongpassage types is maintained seasonally in most cases, but foxes, dogs, rabbits and small mammals have shown significativechanges of passage type use between seasons.

452 C. Mata et al. / Transportation Research Part D 14 (2009) 447–452

The change most frequently detected points to a preferential use of passages under the road in summer substituting theuse of wildlife overpasses in winter. Reasons for this change are unknown but two complementary hypothesis stand out: (i)the increased traffic perturbation in summer may prevent the use of overpasses by animals, and (ii) water runoff may reducethe use of riverbeds by animals for their movements in winter, leading to a reduction in the use of culverts and other struc-tures located in low positions.

On the one hand, traffic duplication in summer leads to an increase in average nightly noise levels of approximately 2.3 dBA in the surroundings of wildlife overpasses with peak values over 85 dB A (C. Iglesias, unpublished data) and car noise pre-vents the use of road crossing structures by some species like deer (Gagnon et al., 2007b). Moreover, light disturbance byheadlamps may also deter animals from crossing over the road and wildlife overpasses in the area do not have solid screensas prescribed to avoid animal disturbance (Iuell et al., 2003) while other overpasses in the stretch are only protected by0.85 m concrete walls.

On the other hand, some studies have already detected the reluctance to use crossing structures carrying water by smallmammals and carnivores (Rosell et al., 1997), and rabbits are known to avoid damp grasslands and flooded sites (McBride,1988). Although changes found in the case of small mammals are more complex, they could also point to some winter avoid-ance of culverts due to flooding.

From an applied perspective, our results point to the relevance of taking into account seasonality for the design of monitoringprogrammes. Thus, in areas with marked seasons or with species of concern that may change their movements seasonally it isadvisable to monitor the permeability of the infrastructure for vertebrates at least twice a year (Gloyne and Clevenger, 2001).Data analysis after one or two years of seasonal monitoring may show low seasonality and allow a reduction in monitoringintensity afterwards. In areas without the above mentioned concerns and in cases where budget limitations restrict monitoringto one campaign per year, it is anyhow important to match it to the season of stronger animal activity (e.g. after breeding orduring dispersal). Regarding seasonality, changes in traffic intensity along the year should be also taken into account for the de-sign of monitoring. Moreover, the effect of disturbance by traffic on the effectiveness of mitigation measures for fauna needs tobe evaluated in detail, as some evidence is arising about its potential relevance (Gagnon et al., 2007b).

Acknowledgement

This study was carried out within a UAM-CEDEX research agreement with funds from the Spanish Ministerio de MedioAmbiente. The Comunidad de Madrid funded an FPI grant to Cristina Mata and supports the research group through REME-DINAL Research Network (S-0505/AMB/0335). Heiko G. Rödel helped us with statistical analyses and comments by A. Rod-ríguez, S. Riley and two anonymous referees improved an initial draft of the manuscript.

References

Bang, P., Dahlstrom, P., 2001. Animal Tracks and Signs. Oxford University Press, Oxford.Blanco, J.C., 1998. Mamíferos de España I y II. Editorial Planeta, SA, Barcelona.Faraway, J.J., 2005. Linear Models. R. Chapman and Hall/CRC.Fedriani, J.M., Delibes, M., Ferreras, P., Roman, J., 2002. Local and landscape habitat determinants of water vole distribution in a patchy Mediterranean

environment. Ecoscience 9, 11–20.Fomento. 2002. Mapa de Tráfico 2002. CD-Rom. Ministerio de Fomento, Madrid, Spain.Fomento. 2003. Mapa de Tráfico 2003. CD-Rom. Ministerio de Fomento, Madrid, Spain.Forman, R., Sperling, D., Bissonette, J.A., Clevenger, A.P., Cutshall, C.D., Dale, V.H., Fahrig, L., France, R., Goldman, C.R., Heanue, K., 2003. Road Ecology: Science

and Solutions. Island Press, Washington, DC.Gagnon, J.W., Theimer, T.C., Dodd, N.L., Boe, S., Schweinsburg, R.E., 2007a. Traffic volume alters Elk distribution and highway crossings in Arizona. Journal of

Wildlife Management 71, 2318–2323.Gagnon, J.W., Theimer, T.C., Dodd, N.L., Manzo, A.L., Schweinsburg, R.E., 2007b. Effects of traffic on Elk use of wildlife underpasses in Arizona. Journal of

Wildlife Management 71, 2324–2328.Gloyne, C.C., Clevenger, A.P., 2001. Cougar Puma concolor use of wildlife crossing structures on the Trans-Canada highway in Banff National Park, Alberta.

Wildlife Biology 7, 117–124.Haddad, N.M., Rosenberg, D.K., Noon, B.R., 2000. On experimentation and the study of corridors: response to Beier and Noss. Conservation Biology 14, 1543–

1545.Iuell, B., Bekker, G.J., Cuperus, R., Dufek, J., Fry, G., Hicks, C., Hlavác, V.B., Rosell, C., Sangwine, T., Torslov, N., 2003. Wildlife and Traffic: A European Handbook

for Identifying Conflicts and Designing Solutions. KNNV Publishers, Zeist.Malo, J.E., Hervás, I., Mata, C., Herranz, J., Suárez, F., 2005. How many days to monitor a wildlife passage? Species detection patterns and the estimation of

vertebrate fauna using crossing structures in a motorway. In: Leroy, C., Irwin, P.G., McDermott, K.P., Raleigh, N.C. (Eds.) Proceedings of the InternationalConference on Ecology and Transportation. Centre for Transportation and the Environment, North Carolina State University.

Mata, C., Hervás, I., Herranz, J., Suárez, F., Malo, J.E., 2005. Complementary use by vertebrates of crossing structures along a fenced Spanish motorway.Biological Conservation 124, 397–405.

Mata, C., Hervás, I., Herranz, J., Suárez, F., Malo, J.E., 2006. Monitoring wildlife use of crossing structures on motorways: should we use footprints orphotographic systems? In: First European Congress of Conservation Biology, Eger.

McBride, A., 1988. Rabbits and Hares. Whittet Books, London.McGregor, R.L., Bender, D.J., Fahrig, L., 2008. Do small mammals avoid roads because of the traffic? Journal of Applied Ecology 45, 117–123.Rice, W.R., 1989. Analyzing tables of statistical tests. Evolution 43, 223–225.Rodríguez, A., Crema, G., Delibes, M., 1996. Use of non-wildlife passages across a high speed railway by terrestrial vertebrates. Journal of Applied Ecology 33,

1527–1540.Rosell, C., Parpal, J., Campeny, R., Jové, S., Pasquina, A., Velasco, J.M., 1997. Mitigation of barrier effect of linear infrastructures to wildlife. In: Canters, K. (Ed.),

Habitat Fragmentation and Infrastructure Maastricht. The Hague, Ministry of Transport, Public Works and Water Management, Delft.Trombulak, S.C., Frissell, C.A., 2000. The ecological effects of roads on terrestrial and aquatic communities: a review. Conservation Biology 14, 18–30.Yanes, M., Velasco, J.M., Suárez, F., 1995. Permeability of roads and railways to vertebrate: the importance of culverts. Biological Conservation 71, 217–222.