crossing structures (Dorsey et al. 2015; Jackson and Griffin 2000; van der Grift
1999). Railways have already been recognized as potential ecological barriers,
namely for large mammals (Ito et al. 2013, and see also Chap. 14), a similar and
cumulative effect with that of roads (see Chap. 4). Therefore, the generalized use of
barriers along railways should be discouraged (Dorsey et al. 2015; Ito et al. 2013;
Jackson and Griffin 2000). Barriers should be erected only along the stretches with
high incidence of wildlife-train collisions, i.e., mortality hotspots.
Exclusion fences are currently considered to be the most effective means to
restrict wildlife access to railways (Ito et al. 2013; van der Grift 1999) being,
probably, the best cost-effective measure to mitigate wildlife mortality in the long
run (Dorsey et al. 2015). However, fences may be less effective for species capable
of climbing, jumping over, or digging under them (Jackson and Griffin 2000).
When fencing is used, it is crucial to provide escapes to avoid animals becoming
trapped between fences on both sides of the railway (Jackson and Griffin 2000).
One-way gates or returning ramps should be regularly installed in places where
animal crossing is more intense. Short retaining walls can be efficient barriers for
reptiles, amphibians and small mammals (Jackson and Griffin 2000). While leaving
a small passage close to the ground (like raising the lower wire of fences) may
reduce the barrier effect for smaller and more agile species, it still prevents the
access of livestock to the railway (Ito et al. 2013).
Olfactory repellents consist of chemicals applied on structures or on the vegetation along the railway (e.g., Andreassen et al. 2005; Kušta et al. 2015). The aim
of olfactory repellents is to drive animals away from the structure or to keep them
more alert, and thus more prone to evade approaching trains. There are several
types of olfactory repellents used for scent-marking, namely synthetic products of
predator substances (Lutz 1994; Andreassen et al. 2005). In Norway, Andreassen
et al. (2005) sprayed a repellant on trees and bamboo canes at 5 m intervals along
the railway, and found that it had an effect on reducing moose casualties, although
with variable efficiency. In the Czech Republic, the application of odor repellents
reduced overall animal mortality on roads and railways, but it was not effective for
reptiles or amphibians (Kušta et al. 2015). In addition, repellants seem to be less
effective at low temperatures (Castiov 1999; Kušta et al. 2015).
Sound signalling and sound-barriers can represent a promising alternative
mitigation measure, especially if they do not greatly limit movements across railways. Sound signalling consists of warning animals of approaching trains
(Babińska-Werka et al. 2015), while sound barriers are mostly intended to keep
animals off the railway. Stationary systems can be mounted in critical areas, using a
motion-activated sensor triggering an audio (and sometimes also visual) stimulus to
frighten the animals. Alternatively, stationary systems can be activated only when
there is a train coming. Electronic systems can also be installed on the front of the
trains. Displayed sounds can be audible or ultrasonic to humans depending on the
target species. For instance, trains equipped with ultrasonic wildlife warning contributed to the reduction of moose-train collisions along a railway in Canada (Muzzi
and Bisset 1990). Babińska-Werka et al. (2015) studied the effectiveness of an
acoustic wildlife warning device in reducing casualties along railways. The sound
34
F. Carvalho et al.
1999). Railways have already been recognized as potential ecological barriers,
namely for large mammals (Ito et al. 2013, and see also Chap. 14), a similar and
cumulative effect with that of roads (see Chap. 4). Therefore, the generalized use of
barriers along railways should be discouraged (Dorsey et al. 2015; Ito et al. 2013;
Jackson and Griffin 2000). Barriers should be erected only along the stretches with
high incidence of wildlife-train collisions, i.e., mortality hotspots.
Exclusion fences are currently considered to be the most effective means to
restrict wildlife access to railways (Ito et al. 2013; van der Grift 1999) being,
probably, the best cost-effective measure to mitigate wildlife mortality in the long
run (Dorsey et al. 2015). However, fences may be less effective for species capable
of climbing, jumping over, or digging under them (Jackson and Griffin 2000).
When fencing is used, it is crucial to provide escapes to avoid animals becoming
trapped between fences on both sides of the railway (Jackson and Griffin 2000).
One-way gates or returning ramps should be regularly installed in places where
animal crossing is more intense. Short retaining walls can be efficient barriers for
reptiles, amphibians and small mammals (Jackson and Griffin 2000). While leaving
a small passage close to the ground (like raising the lower wire of fences) may
reduce the barrier effect for smaller and more agile species, it still prevents the
access of livestock to the railway (Ito et al. 2013).
Olfactory repellents consist of chemicals applied on structures or on the vegetation along the railway (e.g., Andreassen et al. 2005; Kušta et al. 2015). The aim
of olfactory repellents is to drive animals away from the structure or to keep them
more alert, and thus more prone to evade approaching trains. There are several
types of olfactory repellents used for scent-marking, namely synthetic products of
predator substances (Lutz 1994; Andreassen et al. 2005). In Norway, Andreassen
et al. (2005) sprayed a repellant on trees and bamboo canes at 5 m intervals along
the railway, and found that it had an effect on reducing moose casualties, although
with variable efficiency. In the Czech Republic, the application of odor repellents
reduced overall animal mortality on roads and railways, but it was not effective for
reptiles or amphibians (Kušta et al. 2015). In addition, repellants seem to be less
effective at low temperatures (Castiov 1999; Kušta et al. 2015).
Sound signalling and sound-barriers can represent a promising alternative
mitigation measure, especially if they do not greatly limit movements across railways. Sound signalling consists of warning animals of approaching trains
(Babińska-Werka et al. 2015), while sound barriers are mostly intended to keep
animals off the railway. Stationary systems can be mounted in critical areas, using a
motion-activated sensor triggering an audio (and sometimes also visual) stimulus to
frighten the animals. Alternatively, stationary systems can be activated only when
there is a train coming. Electronic systems can also be installed on the front of the
trains. Displayed sounds can be audible or ultrasonic to humans depending on the
target species. For instance, trains equipped with ultrasonic wildlife warning contributed to the reduction of moose-train collisions along a railway in Canada (Muzzi
and Bisset 1990). Babińska-Werka et al. (2015) studied the effectiveness of an
acoustic wildlife warning device in reducing casualties along railways. The sound
34
F. Carvalho et al.