Train-related mortality can directly prevent connectivity among sub-populations, or
reduce their reproductive success, if individuals seeking mates die or if their offspring are railway-killed. Wildlife-train collisions (hereinafter “WTC”) are the most
commonly documented source of animal mortality, although electrocution or collisions with wires can also occur (Rodríguez et al. 2008; Dorsey et al. 2015).
A recently documented source of mortality is that of cavity nester birds in uncapped
catenary poles from HSR in Spain, as these tubular poles act as pitfall traps for
birds, because poles have smooth internal walls, not allowing birds that enter them
to fall down to fly out (Malo et al. 2016). As the drainage hole at the base of the
pole is too narrow to allow trapped birds to escape, the problem could be readily
solved by simply capping the tops of all types of tubular poles (Malo et al. 2016).
A non-exclusive mitigation alternative would be to widen drainage holes.
Most of our understanding about railway impacts on wildlife comes from studies
focused on large mammal railway-kills, as they are the most conspicuous, and can
cause accidents, delays to the trains’ operation, significant damage to trains due to
their large size, and, overall, significant financial losses (Dorsey et al. 2015, and also
Chap. 17). Among train-related factors influencing the rates of WTC, traffic flow is
the most important one, with the highest mortality occurring, in fact, in lines with
moderate traffic flow because higher traffic volume deters animals from attempting to
cross (Dorsey et al. 2015). For instance, in the USA, the killing by trains of black
bears (Ursus americanus) attempting to cross areas with low vegetation cover
through train bridges in lines with moderate traffic has been documented (van Why
and Chamberlain 2003). The existence of lapses of time without traffic encourages
the bears to cross the valley by the bridge, and these are railway-killed when a train
arrives and they cannot jump off the railway bed (van Why and Chamberlain 2003).
Animal behavior also determines their mortality rates. The isotope analyses
using brown bear (U. arctos) hair in Canada showed that some individuals fed on
carcasses from train-killed animals, or on plants growing in railway verges
(Hopkins et al. 2014; see also Wells et al. 1999; see also Chap. 9). Similarly,
granivore species in Canada consumed grain spilled by wagons (Wells et al. 1999),
and in Norway moose (Alces alces) took advantage of the availability of branches
resulting from logging activities in the right-of-way (Gundersen et al. 1998). On the
contrary, despite Cerboncini et al. (2016) trapped more small mammals close to the
tracks in Brazil, their body condition was similar to that of animals trapped far from
the railway. Thus, it seems that this guild of Atlantic forest specialists was not
taking advantage of grain falling from trains (Cerboncini et al. 2016). Railways can
also facilitate the movements of some species, as wildlife uses these homogeneous
surfaces for travelling faster. This was the case of moose and wolves (Canis
lupus) in Canada, and moose and roe deer (Capreolus capreolus) in Sweden, when
snow was very deep (Child 1983; Paquet and Callaghan 1996; Eriksson 2014), of
brown bears in Slovenia, when the terrain was steep (Kaczensky et al. 2003).
One frequently neglected issue is to what extent WTCs could affect population
dynamics. In some species, this impact seems small, but in others it could be
important. This impact can also vary at the population level, as was the case of
different moose populations in the USA, with WTCs ranging from less than 1%
4 Railways as Barriers for Wildlife: Current Knowledge
47
reduce their reproductive success, if individuals seeking mates die or if their offspring are railway-killed. Wildlife-train collisions (hereinafter “WTC”) are the most
commonly documented source of animal mortality, although electrocution or collisions with wires can also occur (Rodríguez et al. 2008; Dorsey et al. 2015).
A recently documented source of mortality is that of cavity nester birds in uncapped
catenary poles from HSR in Spain, as these tubular poles act as pitfall traps for
birds, because poles have smooth internal walls, not allowing birds that enter them
to fall down to fly out (Malo et al. 2016). As the drainage hole at the base of the
pole is too narrow to allow trapped birds to escape, the problem could be readily
solved by simply capping the tops of all types of tubular poles (Malo et al. 2016).
A non-exclusive mitigation alternative would be to widen drainage holes.
Most of our understanding about railway impacts on wildlife comes from studies
focused on large mammal railway-kills, as they are the most conspicuous, and can
cause accidents, delays to the trains’ operation, significant damage to trains due to
their large size, and, overall, significant financial losses (Dorsey et al. 2015, and also
Chap. 17). Among train-related factors influencing the rates of WTC, traffic flow is
the most important one, with the highest mortality occurring, in fact, in lines with
moderate traffic flow because higher traffic volume deters animals from attempting to
cross (Dorsey et al. 2015). For instance, in the USA, the killing by trains of black
bears (Ursus americanus) attempting to cross areas with low vegetation cover
through train bridges in lines with moderate traffic has been documented (van Why
and Chamberlain 2003). The existence of lapses of time without traffic encourages
the bears to cross the valley by the bridge, and these are railway-killed when a train
arrives and they cannot jump off the railway bed (van Why and Chamberlain 2003).
Animal behavior also determines their mortality rates. The isotope analyses
using brown bear (U. arctos) hair in Canada showed that some individuals fed on
carcasses from train-killed animals, or on plants growing in railway verges
(Hopkins et al. 2014; see also Wells et al. 1999; see also Chap. 9). Similarly,
granivore species in Canada consumed grain spilled by wagons (Wells et al. 1999),
and in Norway moose (Alces alces) took advantage of the availability of branches
resulting from logging activities in the right-of-way (Gundersen et al. 1998). On the
contrary, despite Cerboncini et al. (2016) trapped more small mammals close to the
tracks in Brazil, their body condition was similar to that of animals trapped far from
the railway. Thus, it seems that this guild of Atlantic forest specialists was not
taking advantage of grain falling from trains (Cerboncini et al. 2016). Railways can
also facilitate the movements of some species, as wildlife uses these homogeneous
surfaces for travelling faster. This was the case of moose and wolves (Canis
lupus) in Canada, and moose and roe deer (Capreolus capreolus) in Sweden, when
snow was very deep (Child 1983; Paquet and Callaghan 1996; Eriksson 2014), of
brown bears in Slovenia, when the terrain was steep (Kaczensky et al. 2003).
One frequently neglected issue is to what extent WTCs could affect population
dynamics. In some species, this impact seems small, but in others it could be
important. This impact can also vary at the population level, as was the case of
different moose populations in the USA, with WTCs ranging from less than 1%
4 Railways as Barriers for Wildlife: Current Knowledge
47