(Belant 1995) to 70% (Schwartz and Bartley 1991) of the estimated population size,
or 5% of adult radio-collared animals (n = 204; Modafferi and Becker 1997). For
brown bears, it varied from 5% of radio-tracked animals in the USA (n = 43; Waller
and Servheen 2005) to 18% in Slovenia (n = 17; Kaczensky et al. 2003). The
mortality due to collisions with trains affected 5% (n = 21) of the radio-tagged eagle
owls (Bubo bubo) in Switzerland, with WTCs being less important than electrocution and cable or car collisions (Schaub et al. 2010). However, all these figures
provide little information without the corresponding population viability analyses
(PVAs). In this sense, the latter paper estimated an annual 31% of population growth
if the entire anthropogenic mortality of eagle owls was eliminated, but without
information on the effects of removing WTCs alone (Schaub et al. 2010).
Habitat Loss and Fragmentation
Habitat loss takes place when railway construction leads to the reduction of the
available habitat, since the transformed railway bed is unsuitable for several species.
Habitat fragmentation is often, but not necessarily, mediated by habitat loss. During
fragmentation, large, continuous fragments are divided resulting in smaller, often
isolated, patches that may not be able to maintain viable populations in the long run
(Fahrig 2003). Whereas general information on habitat fragmentation is abundant
(see Fahrig 2003 for a review), studies exclusively focused on railway-related
fragmentation are non-existent, because researchers did not differentiate between
railway- and road-related fragmentation, assessing these two different infrastructures
as a whole (e.g., Jaeger et al. 2007; Girvetz et al. 2008; Bruschi et al. 2015).
When a population’s territory is bisected by a railway, part of its habitat is lost,
and the remainder may be degraded, usually via cascade effects. The latter is what is
happening to the woodland caribous (Rangifer tarandus) in Canada, as the construction of railways and other linear infrastructures facilitated the access of wolves
to remote areas where there are still populations of this ungulate, being their viability threatened (James and Stuart-Smith 2000; Whittington et al. 2011).
Habitat changes also take place in railway corridors, as their verges commonly
differ from the surrounding landscape, but are homogeneous along the railway
network. These changes can be exploited by generalist species or by opportunistic
individuals, using them as shelters or corridors. They can be used by invasive
species as well (for more details on the latter, see Chap. 5). Some authors have
suggested that the creation of new habitats by mowing the right-of-way, and the
presence of associated structures like powerlines and their pylons, provide new
opportunities for several species to breed or hunt (see Morelli et al. 2014 regarding
birds). For instance, Vandevelde et al. (2014) (see Chap. 16) found that in France,
in intensive agricultural landscapes, where linear semi-natural elements like
hedgerows tend to disappear, bat species that forage in more open habitats benefited
from railway verges. For Polish butterflies, railways not only acted as corridors, but
also sheltered greater species richness than forest clearings or degraded meadows
48
R. Barrientos and L. Borda-de-Água
or 5% of adult radio-collared animals (n = 204; Modafferi and Becker 1997). For
brown bears, it varied from 5% of radio-tracked animals in the USA (n = 43; Waller
and Servheen 2005) to 18% in Slovenia (n = 17; Kaczensky et al. 2003). The
mortality due to collisions with trains affected 5% (n = 21) of the radio-tagged eagle
owls (Bubo bubo) in Switzerland, with WTCs being less important than electrocution and cable or car collisions (Schaub et al. 2010). However, all these figures
provide little information without the corresponding population viability analyses
(PVAs). In this sense, the latter paper estimated an annual 31% of population growth
if the entire anthropogenic mortality of eagle owls was eliminated, but without
information on the effects of removing WTCs alone (Schaub et al. 2010).
Habitat Loss and Fragmentation
Habitat loss takes place when railway construction leads to the reduction of the
available habitat, since the transformed railway bed is unsuitable for several species.
Habitat fragmentation is often, but not necessarily, mediated by habitat loss. During
fragmentation, large, continuous fragments are divided resulting in smaller, often
isolated, patches that may not be able to maintain viable populations in the long run
(Fahrig 2003). Whereas general information on habitat fragmentation is abundant
(see Fahrig 2003 for a review), studies exclusively focused on railway-related
fragmentation are non-existent, because researchers did not differentiate between
railway- and road-related fragmentation, assessing these two different infrastructures
as a whole (e.g., Jaeger et al. 2007; Girvetz et al. 2008; Bruschi et al. 2015).
When a population’s territory is bisected by a railway, part of its habitat is lost,
and the remainder may be degraded, usually via cascade effects. The latter is what is
happening to the woodland caribous (Rangifer tarandus) in Canada, as the construction of railways and other linear infrastructures facilitated the access of wolves
to remote areas where there are still populations of this ungulate, being their viability threatened (James and Stuart-Smith 2000; Whittington et al. 2011).
Habitat changes also take place in railway corridors, as their verges commonly
differ from the surrounding landscape, but are homogeneous along the railway
network. These changes can be exploited by generalist species or by opportunistic
individuals, using them as shelters or corridors. They can be used by invasive
species as well (for more details on the latter, see Chap. 5). Some authors have
suggested that the creation of new habitats by mowing the right-of-way, and the
presence of associated structures like powerlines and their pylons, provide new
opportunities for several species to breed or hunt (see Morelli et al. 2014 regarding
birds). For instance, Vandevelde et al. (2014) (see Chap. 16) found that in France,
in intensive agricultural landscapes, where linear semi-natural elements like
hedgerows tend to disappear, bat species that forage in more open habitats benefited
from railway verges. For Polish butterflies, railways not only acted as corridors, but
also sheltered greater species richness than forest clearings or degraded meadows
48
R. Barrientos and L. Borda-de-Água