and openness (relative width-length of underpasses) and remain dry (at least
partially) for most of the year (Baofa et al. 2006; Jackson and Griffin 2000;
Yanes et al. 1995). Some species, such as rabbits, seem to prefer underpasses
where it is possible to see the opposite end (Rosell et al. 1997).
3. Substrate, moisture, temperature, and light. These characteristics of crossing
structures will influence their use by animals (Glista et al. 2009; Jackson and
Griffin 2000; Rosell et al. 1997). The set of adequate conditions can be
species-specific, but in general animals prefer crossing structures with a natural
substrate, no temperature differences, and natural light (avoiding dark or artificially lit structures). Amphibians in particular require moist conditions.
4. Approaching habitat. The habitat near passing structures should be attractive to
animals; in particular, the presence of covers, or their absence, may determine
the use of crossing structures by some species (Baofa et al. 2006; Jackson and
Griffin 2000; Rodríguez et al. 1996; Yanes et al. 1995).
5. Guiding structures. Fences and barrier walls guiding wildlife to crossing
structures maximize their effectiveness (Jackson and Griffin 2000). For example,
in Florida, the implementation of a barrier wall in conjunction with a culvert
system reduced the road mortality of vertebrate species (excluding hylid treefrogs) by 94% (Dodd et al. 2004).
6. Disturbance. The use of crossing structures by humans and vehicles should be
reduced as much as possible (Baofa et al. 2006; Clevenger and Waltho 2000).
Noisy underpasses are likely to be avoided by more sensitive species (Jackson
and Griffin 2000).
7. Interspecific interactions. The regular use of passages by predators may discourage their use by potential prey species (Clevenger and Waltho 1999, 2000).
Habitats frequently used by predators of the target species should then be
avoided—namely, the preferred hunting grounds and core areas of the home
range of predators.
Although crossing structures can strongly contribute to reducing the mortality of
non-flying animals, they are less effective in preventing collisions of birds and bats
with trains, as these animals fly above the railway (Tremblay and St. Clair 2009).
The exception to this are the large railway bridges and viaducts going over
watercourses and valleys, in which the large size of the crossing structure facilitates
the movement of birds and bats beneath the railway (Tremblay and St. Clair 2009).
Structures that Restrict Wildlife Access to Railways
One of the most effective measures for reducing wildlife mortality in railways is the
implementation of structures that prevent crossing or, in the case of flying animals,
forcing the crossing above the trains and overhead wires (Dorsey et al. 2015; Glista
et al. 2009; van der Grift 1999). However, the application of measures that restrict
movements will inevitably increase barrier effects, unless accompanied by adequate
3 Methods to Monitor and Mitigate Wildlife Mortality in Railways
33
partially) for most of the year (Baofa et al. 2006; Jackson and Griffin 2000;
Yanes et al. 1995). Some species, such as rabbits, seem to prefer underpasses
where it is possible to see the opposite end (Rosell et al. 1997).
3. Substrate, moisture, temperature, and light. These characteristics of crossing
structures will influence their use by animals (Glista et al. 2009; Jackson and
Griffin 2000; Rosell et al. 1997). The set of adequate conditions can be
species-specific, but in general animals prefer crossing structures with a natural
substrate, no temperature differences, and natural light (avoiding dark or artificially lit structures). Amphibians in particular require moist conditions.
4. Approaching habitat. The habitat near passing structures should be attractive to
animals; in particular, the presence of covers, or their absence, may determine
the use of crossing structures by some species (Baofa et al. 2006; Jackson and
Griffin 2000; Rodríguez et al. 1996; Yanes et al. 1995).
5. Guiding structures. Fences and barrier walls guiding wildlife to crossing
structures maximize their effectiveness (Jackson and Griffin 2000). For example,
in Florida, the implementation of a barrier wall in conjunction with a culvert
system reduced the road mortality of vertebrate species (excluding hylid treefrogs) by 94% (Dodd et al. 2004).
6. Disturbance. The use of crossing structures by humans and vehicles should be
reduced as much as possible (Baofa et al. 2006; Clevenger and Waltho 2000).
Noisy underpasses are likely to be avoided by more sensitive species (Jackson
and Griffin 2000).
7. Interspecific interactions. The regular use of passages by predators may discourage their use by potential prey species (Clevenger and Waltho 1999, 2000).
Habitats frequently used by predators of the target species should then be
avoided—namely, the preferred hunting grounds and core areas of the home
range of predators.
Although crossing structures can strongly contribute to reducing the mortality of
non-flying animals, they are less effective in preventing collisions of birds and bats
with trains, as these animals fly above the railway (Tremblay and St. Clair 2009).
The exception to this are the large railway bridges and viaducts going over
watercourses and valleys, in which the large size of the crossing structure facilitates
the movement of birds and bats beneath the railway (Tremblay and St. Clair 2009).
Structures that Restrict Wildlife Access to Railways
One of the most effective measures for reducing wildlife mortality in railways is the
implementation of structures that prevent crossing or, in the case of flying animals,
forcing the crossing above the trains and overhead wires (Dorsey et al. 2015; Glista
et al. 2009; van der Grift 1999). However, the application of measures that restrict
movements will inevitably increase barrier effects, unless accompanied by adequate
3 Methods to Monitor and Mitigate Wildlife Mortality in Railways
33