(>10 km), but their detectability as proved to be lower (Garrah et al. 2015). Once a
carcass is found, and depending on its state of decay, several variables should be
recorded: species, age, sex, GPS location, time of day, weather conditions, position
on the railway (verges, between lines, rock ballast, etc.), and surrounding habitat
(Santos et al. 2011; Wells et al. 1999).
Surveys should be systematic, but their temporal frequency depends on species
traits and biology. For small animals such as passerines, small mammals or bats,
daily surveys are needed to reduce bias on estimates due to lower carcass persistence time (Santos et al. 2011, 2015). Santos et al. (2011) showed in a road study
that sampling at intervals greater than one day results in the loss of 60% of the
casualties for small animals (<500 g), and reaches 73 and 85% for lizards and bats,
respectively. By contrast, they found that larger animals (>500 g, e.g., birds of prey
and carnivores) persist for more than two days on average, which can be used as a
baseline for their monitoring (Santos et al. 2011). In order to obtain a good balance
among costs and survey frequency, the priority should be given to the animals’
activity peaks, including those during dispersal, migration, and hunting seasons
(Costa et al. 2015; Stevens and Dennis 2013). After the beginning of the railway
operations, and in order to get a good evaluation of mortality estimates, monitoring
should cover a minimum period of 3 years, so that animals adapt to the new
environment (Iuell et al. 2003).
On electrified railways the risk of bird and bat mortality increases due to collisions with the overhead electric lines. Additionally, the electrocution of birds can
occur at pylons and wherever the cable isolation has flaws (Kušta et al. 2011; Peña
and Llama 1997). Because overhead electric lines are placed at the sides of the rails,
animals killed by electrocution may be projected further away than those suffering
collisions with trains, thus decreasing their detectability. Accordingly, to obtain
accurate estimates on mortality when there are electric components (overhead
electric lines and pylons), surveys should be done daily, and if possible, supported
by search dogs, as these dogs have been shown to be more efficient than humans at
detecting carcasses under power lines (73 vs. 20%) and at wind farms (Mathews
et al. 2013).
Review of the Methods Used on Wildlife Mortality Surveys
Most studies addressing mortality on railways rely on incidental reports provided
by the railway staff (van der Grift and Kuijsters 1998). Few have described their
methods exhaustively (Seiler and Helldin 2006), and most do not report the
monitoring frequency (e.g., Cserkész and Farkas 2015; van der Grift and Kuijsters
1998), or the methodology used (Jaren et al. 1991). Typically, studies used one of
the following survey methods:
• Surveys by rail companies’ workers and non-expert citizens
These surveys are characterized by fortuitous observations. Reports of collisions are
often done by train drivers, and occasionally by maintenance crew personnel, who
3 Methods to Monitor and Mitigate Wildlife Mortality in Railways
27
carcass is found, and depending on its state of decay, several variables should be
recorded: species, age, sex, GPS location, time of day, weather conditions, position
on the railway (verges, between lines, rock ballast, etc.), and surrounding habitat
(Santos et al. 2011; Wells et al. 1999).
Surveys should be systematic, but their temporal frequency depends on species
traits and biology. For small animals such as passerines, small mammals or bats,
daily surveys are needed to reduce bias on estimates due to lower carcass persistence time (Santos et al. 2011, 2015). Santos et al. (2011) showed in a road study
that sampling at intervals greater than one day results in the loss of 60% of the
casualties for small animals (<500 g), and reaches 73 and 85% for lizards and bats,
respectively. By contrast, they found that larger animals (>500 g, e.g., birds of prey
and carnivores) persist for more than two days on average, which can be used as a
baseline for their monitoring (Santos et al. 2011). In order to obtain a good balance
among costs and survey frequency, the priority should be given to the animals’
activity peaks, including those during dispersal, migration, and hunting seasons
(Costa et al. 2015; Stevens and Dennis 2013). After the beginning of the railway
operations, and in order to get a good evaluation of mortality estimates, monitoring
should cover a minimum period of 3 years, so that animals adapt to the new
environment (Iuell et al. 2003).
On electrified railways the risk of bird and bat mortality increases due to collisions with the overhead electric lines. Additionally, the electrocution of birds can
occur at pylons and wherever the cable isolation has flaws (Kušta et al. 2011; Peña
and Llama 1997). Because overhead electric lines are placed at the sides of the rails,
animals killed by electrocution may be projected further away than those suffering
collisions with trains, thus decreasing their detectability. Accordingly, to obtain
accurate estimates on mortality when there are electric components (overhead
electric lines and pylons), surveys should be done daily, and if possible, supported
by search dogs, as these dogs have been shown to be more efficient than humans at
detecting carcasses under power lines (73 vs. 20%) and at wind farms (Mathews
et al. 2013).
Review of the Methods Used on Wildlife Mortality Surveys
Most studies addressing mortality on railways rely on incidental reports provided
by the railway staff (van der Grift and Kuijsters 1998). Few have described their
methods exhaustively (Seiler and Helldin 2006), and most do not report the
monitoring frequency (e.g., Cserkész and Farkas 2015; van der Grift and Kuijsters
1998), or the methodology used (Jaren et al. 1991). Typically, studies used one of
the following survey methods:
• Surveys by rail companies’ workers and non-expert citizens
These surveys are characterized by fortuitous observations. Reports of collisions are
often done by train drivers, and occasionally by maintenance crew personnel, who
3 Methods to Monitor and Mitigate Wildlife Mortality in Railways
27