Physical barrier constraints mainly affect species of small size with reduced
mobility, such as herptiles. For instance, Kornilev et al. (2006) reported that eastern
box turtles (Terrapene carolina) in the USA enter a railway at crossings with roads
(where surfaces are at the same level), but then become trapped between the rails as
they are unable to climb over them, and finally die due to thermal stress. A study of
Hermann’s tortoises (Testudo hermanni) in Romania found that the impossibility of
overtaking obstacles (e.g., ditches with angles of over 60°) led to an increase in the
distribution of railway-kills at the end of the ditches (Iosif 2012).
Bumblebees (Bombus impatiens and B. affinis) in the USA (Bhattacharya et al.
2003) provide an example of a species to which the railway is a behavioral barrier.
These species are reluctant to cross railways (and roads) because of their high fidelity
to their foraging site. In experiments, individuals of these species could come back to
their patches of origin after being translocated, or could leave their patch when their
food was removed, but these movements were rarely in-control (non-translocated)
individuals (Bhattacharya et al. 2003). Bhattacharya et al. (2003) observed that
foraging bees turned back when they reached the edge of a patch (i.e., bisected by a
railway); thus, rather than physically impassable barriers to bumblebees, railways
acted as barriers because they are likely to be strong landmarks. On the other hand,
most of the translocated gatekeeper butterflies (Pyronia tithonus) crossed the French
High Speed Rail (hereinafter “HSR”) to return to their capture plot, as this species
shows a strong homing behavior (Vandevelde et al. 2012; see also Chap. 16).
Mongolian gazelles (Procapra gutturosa) are able to cross fenced railways in
Mongolia (Ito et al. 2008), but they usually do not do so (Ito et al. 2005, 2013, and
see Chap. 14). Therefore, these fenced railways represented a barrier effect affecting
population dynamics as it caused disruptions in long-distance gazelle migrations (Ito
et al. 2005, 2008, 2013). Stopping migration routes prevents gazelles from reaching
their traditional food-rich winter quarters, potentially increasing their winter mortality due to starvation (Ito et al. 2005, 2008, 2013). This conservation problem is
compounded by the current climate change, as drought events reducing vegetation
productivity could require gazelles to migrate longer distances, instead of the current
average of 600 km (Olson et al. 2009). To date, railways do not seem to have been a
barrier for gazelle gene flow, although this assertion should be explored with more
suitable markers (Okada et al. 2012; see below).
Although it has been less studied, the conservation threat of the critically
endangered saiga antelope (Saiga tatarica) in Kazakhstan—as a consequence of
migration disruption due to fenced railways—seems to be similar to that of
Mongolian gazelles (Olson 2013; see also Olson and van der Ree 2015). In a study
carried out in Sweden, Kammonen (2015) found that a motorway and a railway
running in parallel acted as barriers for two bat species (whiskered bat Myotis
mystacinus and Brandt’s bat M. brandtii) in a forest-dominated area. Although this
author did not differentiate between these two infrastructures, she found that bats
did not directly cross them; rather they used either the green bridge or the underpass
both to cross it and to forage (Kammonen 2015).
4 Railways as Barriers for Wildlife: Current Knowledge
45
mobility, such as herptiles. For instance, Kornilev et al. (2006) reported that eastern
box turtles (Terrapene carolina) in the USA enter a railway at crossings with roads
(where surfaces are at the same level), but then become trapped between the rails as
they are unable to climb over them, and finally die due to thermal stress. A study of
Hermann’s tortoises (Testudo hermanni) in Romania found that the impossibility of
overtaking obstacles (e.g., ditches with angles of over 60°) led to an increase in the
distribution of railway-kills at the end of the ditches (Iosif 2012).
Bumblebees (Bombus impatiens and B. affinis) in the USA (Bhattacharya et al.
2003) provide an example of a species to which the railway is a behavioral barrier.
These species are reluctant to cross railways (and roads) because of their high fidelity
to their foraging site. In experiments, individuals of these species could come back to
their patches of origin after being translocated, or could leave their patch when their
food was removed, but these movements were rarely in-control (non-translocated)
individuals (Bhattacharya et al. 2003). Bhattacharya et al. (2003) observed that
foraging bees turned back when they reached the edge of a patch (i.e., bisected by a
railway); thus, rather than physically impassable barriers to bumblebees, railways
acted as barriers because they are likely to be strong landmarks. On the other hand,
most of the translocated gatekeeper butterflies (Pyronia tithonus) crossed the French
High Speed Rail (hereinafter “HSR”) to return to their capture plot, as this species
shows a strong homing behavior (Vandevelde et al. 2012; see also Chap. 16).
Mongolian gazelles (Procapra gutturosa) are able to cross fenced railways in
Mongolia (Ito et al. 2008), but they usually do not do so (Ito et al. 2005, 2013, and
see Chap. 14). Therefore, these fenced railways represented a barrier effect affecting
population dynamics as it caused disruptions in long-distance gazelle migrations (Ito
et al. 2005, 2008, 2013). Stopping migration routes prevents gazelles from reaching
their traditional food-rich winter quarters, potentially increasing their winter mortality due to starvation (Ito et al. 2005, 2008, 2013). This conservation problem is
compounded by the current climate change, as drought events reducing vegetation
productivity could require gazelles to migrate longer distances, instead of the current
average of 600 km (Olson et al. 2009). To date, railways do not seem to have been a
barrier for gazelle gene flow, although this assertion should be explored with more
suitable markers (Okada et al. 2012; see below).
Although it has been less studied, the conservation threat of the critically
endangered saiga antelope (Saiga tatarica) in Kazakhstan—as a consequence of
migration disruption due to fenced railways—seems to be similar to that of
Mongolian gazelles (Olson 2013; see also Olson and van der Ree 2015). In a study
carried out in Sweden, Kammonen (2015) found that a motorway and a railway
running in parallel acted as barriers for two bat species (whiskered bat Myotis
mystacinus and Brandt’s bat M. brandtii) in a forest-dominated area. Although this
author did not differentiate between these two infrastructures, she found that bats
did not directly cross them; rather they used either the green bridge or the underpass
both to cross it and to forage (Kammonen 2015).
4 Railways as Barriers for Wildlife: Current Knowledge
45